Spark plug threaded holes.
Tightening torques. Gaps.
ANTISEIZE... OR NOT?
Spark plug caps.
Resistor & non-resistor spark plugs.
Heat-Range chart; equivalent numbers.
© Copyright, 2013, R. Fleischer
Above is a photo of three types of EXTENDED NOSE spark plugs, 3/4" reach, 14 mm.
Extended nose means that the center white insulator extends beyond the end of the threads.
ONLY THE LEFT-MOST spark plug is appropriate for Airheads; it has a SINGLE
GROUND ELECTRODE AND A STANDARD SIZED CENTER ELECTRODE, WITH AN
The middle spark plug, Bosch XR7LDC, has two ground electrodes, & can be used in
Classic K bikes; these bikes can also use X5D, X5DC, XR5DC. The XLR7DC spark plug
with dual grounding electrodes, introduced during the K1200 production, works well with all
prior K bikes.
The middle & right-most spark plug has even more ground electrodes & versions can have
standard or a fine wire center electrode. These have NO USE in Airheads & NOT in
Classic K bikes if the spark plugs have more than 2 grounding electrodes).
NOTE: Do not try to re-gap the XR7LDC spark plug, even when brand-new.
You can re-gap single ground electrode spark plugs when brand new only.
BMW says NOT
to re-gap spark plugs. BMW did not explain that advice very well.
They really should have added this: ".....AFTER they have been in use". That IS
what BMW means & I am in total agreement. After any spark plug has been in
use the metal structure of the GROUND electrode changes. If you then try to
re-gap the spark plug you WEAKEN the ground electrode. In quite rare instances
they have broken off, causing engine damage.
IN USE here means that the engine has been run. This is especially so after the
engine has been run under load.
As miles accumulate, the electrodes gap increases. This is usually acceptable
until the gap becomes very excessive, at which time marginal systems or those
running very lean or very rich might begin to misfire, leading to poor fuel mileage.
Fine wire tipped precious metal (center electrode) spark plugs are less likely to
have this problem with advancing miles & the spark will find it easier on them to
jump to the ground electrode(s), increasing the life a bit more, but fine wire spark
plugs may not work all that well in some engines. I am OK with you trying them,
but only if they have single ground electrodes if used on Airheads.
The mileage it takes to get to a problem varies highly, with a wide range of things
affecting the wear, such as spark plug heat range, caps resistance, actual mixture
burning conditions, type of ignition system, whether resistor spark plugs or not,
ETC. Spark plugs GENERALLY last a long time now, due to the use of UNleaded
fuels. In the past, leaded fuels would eventually cause electrical shorts/leakage
problems at the center insulator....and it was common to replace spark plugs at
10K-20K; or, to clean them by sand-blasting, & replace them at the next service
interval. They CAN last much longer now. Do NOT expect spark plugs on your
BMW motorcycle to last as long as spark plugs on modern fuel injected cars.
For the Airheads, worn gaps approaching even .040" are often still usable....but
spark plugs should be replaced sooner, especially if the grounding electrode
gets quite thin (usually a dished thinness), as they can weaken. In the OLD OLD
days, we Wrenches would file the ground electrode, sand-blast the plugs, set gaps,
etc. These days, nothing should be done but to check the gap an plug base and
central insulator color and appearance.
Spark plugs screw into threads; these male & female threads are exposed to combustion
heat, pressure & byproducts of gasoline & oil, tending to carbonize, & can accumulate in
the threads. Combustion is not the same in all Airheads, some have a fair amount of burnt
oil or carbonized oil, & other combustion products accumulating in the threads. Worn threads
tend to accumulate MORE hard carbon. The carbon can act like a pretty good abrasive. It
also can act like a cement!
If reinstalling a used spark plug (never re-gap one) I like to clean the threads. If the threads
in the head have the look of excessive deposits I may go so far as to rotate the engine to
exhaust valve open, & blow compressed air into the intake area as I clean the threads. A
greased tap can work, but then you have to degrease the threads and I dislike that taps
will tend to cut head metal, not just the carbon. I mostly use brass gun cleaning brushes,
rotating them for cleaning. I've seen some spark plug threads that were, brand-new, not
made all that nicely. Poor spark plug threads WILL damage the head threads. Poor spark
plug threads have been identified on spark plugs made in various countries.
Aluminum cylinder heads can be damaged relatively easily if one is not careful. There is
a distinct limit to abuse from over-tightening a spark plug, or removing & replacing a spark
plug when the cylinder head spark plug threads are full of combustion byproducts & carbon.
Carbon from such as oil burning, or, the very bad use of oil or grease on the threads, can
get very hard, & very abrasive. It can cause the spark plugs to injure the cylinder head
threads during removal. It is NOT a good idea to put much torque on a spark plug when
attempting to remove it. FIRST try heating the cylinder head. Running the engine is a
good way to do this.
Some BMW motorcycles PRIOR to the /5 series, I will just call them /2 bikes, had some
metal alloy & casting problems, including soft alloys & voids. Even with very careful
torqueing, with the best antiseize compounds of the day, still brought occasional
problems. I've seen poor metals & poor castings bring about failure of the factory installed
'cast-in-place' steel threads inserts, & heat-cool cycling on those early inserts caused
problems. For our /5 & later Airheads, the metal in the heads, & the castings, are very
Many folks simply refuse to use torque wrenches, & some who do or do not, over-torque
spark plugs. I have seen someone over-torque a spark plug & he WAS using a torque
wrench & it WAS set properly. His problem was not realizing that many clicker torque
wrenches tend to be hard to detect the click if the setting is fairly low on the wrench's total
capacity. This tends to be especially so on such as 100+ maximum foot-pound wrenches
which might have a rather subtle click when set low, say around 12 foot-pounds to 18
foot-pounds. Know your wrench. If you don't know what the click feels like at various
settings, and/or are not all that familiar with torque wrenches, especially YOURS, then
put the square end into your bench vise, use soft jaws or protective metal, & test the feel
required for various torque settings, that is, feel & listen for that click. NOTE that "cheap"
beam-type torque wrenches (not meaning the dial indicator commercial types) may be
very INaccurate....& should not be used for critical items.
Abused, the cylinder head spark plug hole threads will eventually start distorting & pulling
out if they don't immediately rip out. While Helicoils or welding & re-machining, all do work
OK, & can even be superior when done correctly, such repairs are usually avoidable if
one takes some extra care in the first place. I don't like to see extra places for sharp bits
of carbon combustion products to adhere to. They create 'hot red glowing places' in the
cylinder heads from using inserts & can cause pre-ignition problems. I recommend
against Time-serts, which can change the spark plug heat value.
I have installed Helicoils, & also have welded up the spark plug thread areas & drilled &
re-tapped them... of course the heads have to come off for that....best to remove the
head in any fix anyway....although one CAN use the official Helicoil Spark Plug Thread
repair kit, with well-greased parts, & with the exhaust valves open so you can blow any
possible chips out with an air hose. You CAN do a good job withOUT removing the head.
It is CRITICAL that drilling & tapping be done squarely.
>>>>ABSOLUTELY AND ALWAYS use a drill guide & tap guide!<<<<
MORE information on installing Helicoils, head on, or head off the engine,
is later in this article.
DO NOT USE GRAPHITE PRODUCTS FOR COATING SPARK PLUG
THREADS. A corrosive type of reaction is possible on the aluminum head.
DO NOT USE GRAPHITE PRODUCTS FOR COATING SPARK PLUG THREADS.
A corrosive type of reaction is possible on the aluminum head.
The use of antiseize is controversial, even among experienced Airhead mechanics....
mostly I think this is due to SOME spark plug manufacturer's literature; & perhaps
some is due to misconceptions. Some is due to faulty belief in old-wives tales, ....or,
possibly, bad experiences from those ham fisted about torquing things. Yes, some
professional wrenches are concerned about YOU, a non-pro, abusing things, & it is
true that use of antiseize COULD (not WILL) make it a somewhat easier to abuse.
SOME manufacturer's, trying to play it safer (???) have changed from recommending
anti-seize, to not recommending it, or just ignoring the use, over the years. NOTE,
however, that a good argument can be made for not using anti-seize, as someone not
knowing the stuff was applied, might then not compensate by reducing the required torque.
I just cannot see any other argument against anti-seize use that is valid....and I can
provide a lot of reasons TO use the stuff.
NOTE: Karle Seyfert, an expert who writes for MOTOR, an INDUSTRY publication,
had an extensive article in MOTOR in March 2013. That article, & some controversy
& comments by one well-known 'guru' in the BMW motorcycle repair business, at
approximately that time on an Internet mailing list, has prompted me to ADD more
commentary to this part of the article you are reading. I have NOT changed my own
practice, intent, or recommendations; but I will give you more information on what
automobile manufacturer's are publishing/recommending!...and some of "WHY!"
Some experienced mechanics believe that if antiseize is used it is 'easier' to over-torque
& damage threads. THAT IS PROBABLY TRUE! BUT, it is true only if the person is
NOT adjusting TORQUE lower, to compensate for the use of anti-seize compound, or,
just being more ham-fisted.
You should be using a torque wrench, AND lowering the official torque value (which is
withOUT antiseize compound unless specifically so-stated). Yes, that means that I
believe the factory torque settings (some, anyway) are too high...even if anti-seize
compound is NOT used, or never has been, on the engine.
Since popular anti-seize compounds act like a lubricant, the applied torque (if that book
value means NO antiseize) MUST be reduced...about 20% reduction is typically
about correct for spark plugs into aluminum.
SOME types of spark plugs, such as taper seat types, are NOT supposed to be used with
regular anti-seize compounds, as they are degree-tightened & so the manufacturer
typically makes a blanket statement not to use anti-seize compounds, applying to all their
spark plugs, rather than providing full information & full information can be slightly more
complicated. BUT: other manufacturers say OK, & give the needed lower torque
values. Some manufacturer's do not mention use of anti-seize at all, & SOME
SAY YOU MUST USE IT!!
Some manufacturer's say they are concerned with HEAT conduction, that is, that the
heat range of the spark plug is or could be changed by the use of anti-seize compound.
Frankly, that IS possible, particularly if the torque used is not correct, but with torque being
reasonable, only a SMALL bit of a single heat range would be the change (at worst case,
otherwise none), & even that would very seldom happen, would have NO EFFECT on your
BMW engine...and I believe any such considerations SHOULD BE IGNORED. I have
NOT seen ANY problem in real life situations if the torque is set properly, even if only
close to proper. I also tested for this, with various torques & test runs on a bike, reading
the spark plugs, and it took a fair amount of torque DEcrease to increase the spark
I have used some sort of anti-seize compound on my own various bikes' spark plugs.
I have over 650,000 miles on BMW's. I use it on my customer's bikes, and on other
besides BMW. It was standard operating procedure (SOP) in my shop to always tell
the customer that if anyone ever removes & replaces spark plugs, that they should
account for the use of anti-seize, even if they don't apply any, as it works into the head
metal somewhat. NO PROBLEMS...EVER. I've NEVER 'pulled' spark plug threads out
of my, nor any of my customer's cylinder heads. I NEVER have problems removing my
spark plugs, & my bikes do NOT wear out their threads, even my /2 with 267K miles.
I am IN FAVOR of using anti-seize compound on spark plug threads. I personally feel
that if the official torque values are reduced (assuming originally specified withOUT
anti-seize compound), & you use the anti-seize compound, you are LESS likely to have
pulled thread problems, heat range will be more consistent, & there will be less problems
with hard particles of carbon that deposit themselves into the cylinder head threads,
which, otherwise, can cause excessive WEAR every time you R/R a spark plug. This
is important, & if you have a two-stroke bike, it is even more important (but, important
Antiseize compounds vary in characteristics, but I have found that all commonly available
ones are OK at the spark plugs.
CAUTION: Using oil or WD40 will tend to eventually result in hard carbon deposits in the
threads, & thus tend to wear the threads & tend to change the effective torque. DO NOT
USE OIL NOR WD40!
Stuck/frozen, or other problem: Some manufacturer's recommend "penetrating oil" for
tight plugs during removal. Most fail to tell you to VERY thoroughly REMOVE that
oil before installing a new spark plug. it is also not easy to get penetrating oil
into the spark plug threads with the head on the engine....but if you can safely
unscrew the spark plug SOME, then you can use a thin oil with the head in place.
A mixture of acetone & automatic transmission oil, ~50-50 works BETTER!
ONCE anti-seize compound is ever used, it tends to work its way into the
aluminum head metal. From that point on, it is best to always use anti-seize
compound. Do not use graphite types as they can cause corrosion problems.
NOTE: Some manuals, such as later Clymers, etc., may tell you to put a dab of anti-seize
compound (often specifying aluminum type) on the spark plug threads before installation;
but, these books may forget to tell you to REDUCE the torque!
Some spark plugs seem to have a bit less diameter or other irregularities with the threads
that can promote carbon or wear. Thread & quality control problems have been reported
on Champion & other spark plugs. It has been reported even on Bosch plugs, if not made
in Germany. OVERALL, German Bosch tolerances seem to be better than some other
spark plug manufacturers. NGK makes a GOOD PRODUCT & I have NEVER seen a
problem with NGK plug manufacturing. Bosch MAY plate the threads, which helps avoid
use of anti-seize, if you are so inclined. NGK plates some spark plug bodies, & on some
threads they put a coating or special treatment. I still use anti-seize on all spark plugs
with standard non-tapered seats.
****The latest NGK literature, specifically mentions using anti-seize compound: it should
be used on the UNplated plugs. I will get into this more deeply HERE:
If you were to access the factory repair manuals for many bikes & cars, you would find that
they are NOT consistent with use of anti-seize compound. Some say you must, some don't
say anything, some say you must not. I've already mentioned some of this, & regarding taper
seat plugs, etc.. Now, we get into this a bit more deeply.
2010 Honda Pilot: Honda says to apply antiseize compound.
2007 Subaru Legacy: gives a torque rating 'without oil on the spark plugs, new plugs'. If
lubricated (does not specify type of lubricant) they say to reduce torque by 'approxmately
1/3 of that specified' to 'avoid overstressing'.
Chevy Cobalt says to NOT use antiseize....because if you DO, you will damage the cylinder head
IF YOU OVERTORQUE.
Service information for a LOT of vehicles not mentioned here were checked. BMW cars, Cadillac,
Dodge, Ford, Hyundai, Mazda, Mercedes-Benz, Porsche, Toyota, VW, Volvo.....all these gave
specific information on torque, but none mentioned anti-seize. I could, obviously, not check for
every model, every year...but, I looked at numerous relatively late model vehicles, & while I did
look at cast iron head engine'd vehicles, I concentrated on aluminum heads.
BMW, motorcycle division, is surprisingly quiet.
NGK, the spark plug manufacturer, gives the strongest advice against using anti-seize...but, in
a way, they also at the SAME TIME give a very strong advice, about why you SHOULD
use anti-seize....at least on THEIR spark plugs. They have an entire technical bulletin on
the subject. Condensing it here for you, they do not want the compound used on plated plugs
(in one place they say all their plugs are like that now...not true, but good enough), & they say
not to use anti-seize compound ON INITIAL INSTALLATION. Then they stop talking about the
plating, & confusingly say that all their plugs are coated with 'special trivalent zinc-chromate shell
plating' which is designed to prevent both corrosion & seizure, eliminating need for compounds
or lubricants. They do not separate the THREADS from the BODY, but it can be implied from
that prior sentence, of course. You must read what NGK says & how, very carefully....because:
Apparently, NGK does not want anyone to remove a spark plug unless a
NEW ONE is then installed.
NGK makes it very difficult to get the information, but here is THEIR information, MY WORDS.
Read this very carefully:
IF...IF...you insist on re-installing an NGK spark plug, even if never actually having run
the engine, you MUST use anti-seize compound. BECAUSE: Once you unscrew the
plug, the NGK super-thin 'plating' coating is, in essence, partially removed permanently,
each time removes more, & the plug can then have galling & other problems.
NGK says nothing directly about what happens to that plating coating, which is another
story entirely. It could be damage-causing, or; well, anything. There is NO INFORMATION.
Autolite spark plug sales information says its plugs are nickel-plated, & says anti-seize compounds
'can have a torque multiplying effect...'....but then says nothing else. However, engineering books
from Autolite say things that contradict its other books' information, & says you MUST USE a
thin-film coating of high-temperature nickel anti-seize...and specifies, specifically, certain plugs &
problems that occur when this is NOT done....in particular the long reach HT plugs (used on Ford
3 valve modular engines, etc...that have WELL-KNOWN plug removal problems).
There is a LOT MORE to all the above; which I abbreviated so as to not bore you too much.
My advice: DO use anti-seize compound, and use my recommended REDUCED torque values.
LOOK at the proper book information. BMW has had various torques, for the same 3/4 reach
14 mm plugs. More later, herein.
I am fine with you using nickel type or copper type of anti-seize compounds. Most anti-seize
compounds contain one or the other or both, & do not specify ...that is, they likely have copper,
but don't say (which contradicts what a certain foul-mouthed maker of videos for BMW bike
repairs says in his videos....about a must to use "copper antiseize').
Amount of torque to use when installing spark plugs:
1. You CAN tighten spark plugs by hand, no torque wrench, once you have a good feel for it,
but use of the torque wrench is HIGHLY recommended. I RECOMMEND YOU USE A
2. I've seen various forces needed to properly seat the crush rings, much of this is because
crush rings vary in how they are made; some are not easily removable from the spark plugs,
so folks don't. Contrary to many books, I am OK with NOT replacing the semi-captive type
crush rings, IF they are in good condition, & IF you use a torque wrench!!! Many books say
1/2 turn on NEW crush rings after the spark plug is JUST seating to the head & rush ring; &
they may also say 1/4 or 1/3 on used crush rings. DO NOT depend on this!
I suggest you do NOT do that on your Airhead nor Classic K.
3. I suggest, strongly, that you use a torque wrench. Keep in mind that not only do you not
want threads pulled, but you also want to maintain the rated spark plug heat value
specification; and, proper torque.
4. Since we all know that many of you are cheapskates & will not use fresh crush rings for
those plugs where they can be removed & replaced, the values I am giving here are
generally safe values, with new or used crush washers/rings...used with a drop of
anti-seize compound spread VERY THINLY onto the clean spark plug threads (fingers work
well for this, you can push the stuff very thinly into the threads). You need NOT cover every
thread....just a wee bit towards the electrodes end THREADS (combustion chamber ends),
pushed into the threads with a finger tip...again, a WEE BIT....is enough. As the plug is
screwed-in, it is spread into the rest of the threads. I personally coat, VERY thinly, all-around.
I use my fingers, or a tiny brush with fairly stiff bristles. The shortened-bristles end of a
common 'acid brush' is perfect if you don't want the stuff on your fingers. DO NOT get
anti-seize compound onto the end of the spark plug area.
3/4" reach, 14 mm, used as top spark plugs, about 14-15 ftlbs. This is the stock top spark
plug size for Airheads.
1/2" reach, 14 mm, about 12-14 ft lbs; this is the commonly used bottom spark plug size on
dual-plug conversions. This torque value is USUALLY...not always... enough to seat the
washer and a tad more. Snug is right. You don't want the plug too loose...if it loosens
and rattles out, that pulls/wears threads. Some have installed smaller spark plugs for
the lower plugs. I've had good results with 8-10 ftlbs for those. Some manuals will show 8-12
in aluminum. Some have installed a welded (to the head) custom-made thick aluminum
washer, or just welded up the material to be thicker, for at the lower spark plug threaded hole,
that allows the top & bottom spark plugs to both be 3/4" reach. If you have this style of lower
spark plug threaded area my recommendation is, as noted above, about 14-15 ftlbs;
EXCEPT if the modification was by an unthreaded spacer, welded or not, then use 14 ftlbs.
With regard to the above various values: UPDATED torque figures, if any, MIGHT be found
in article 71B.
5. One is supposed to, in most older literature, use a brand-new crush washer each time a
plug is removed & replaced, but we all know that most of you won't, & many plugs have the
washers fairly well captive & finding new crush washers is often frustrating. Just be careful
about torque. Many years ago it was common for mechanics to install a fresh washer
each time, and tighten with a common tubular wrench, not a torque wrench, and tighten until
the crush washer was felt to crush & seat, & then increase a certain number of degrees...
and/or by feel. That was done on CAST IRON HEADS. This can still be done, if you have
a decent feel for it, but it is more dangerous to do on aluminum heads. My basic advice
is, and I am hammering you on this with repeating it: wee bit of antiseize, torque
wrench, proper torque.
What about installing Clean and Dry (NOT with anti-seize compound)??
With no anti-seize 'ever' used on your heads, or exceptionally clean threads, you can torque
to 16 footpounds (do not exceed 18) on the TOP plugs. If you have the 1/2" reach 14 mm
bottom plugs, you can go towards 13-14.
18 ftlbs MAXIMUM for clean & dry threads is my personal limit for 3/4" reach plugs, which
are the standard top plugs for Airheads. Clean & Dry here, means NO antiseize, or, none
OFFICIAL BMW Service Information sheet on the late Airheads:
18.4 ftlbs (3/4" reach). Don't use that figure for threads with anti-seize compound.
*****The latest Bosch manuals, for 14 mm spark plugs in BOTH aluminum & cast iron heads,
recommend 7-15 ft lbs. That is NOT oiled NOR antiseized!!! Unfortunately, no further information
about the thread length, is given. MY opinion is that up to 16 is safe on the 3/4 reach plugs....
NOT antiseize coated; but 7 is too low. Best you follow my advice given earlier.
Some years ago it was common was to see 14 mm spark plugs specified in plug manuals at
26-30 ftlbs (!!!) in cast iron; 18-22 ftlbs in aluminum. NO allowance for short or longer thread
types was usually shown. Do NOT use such values!!!
Removing spark plugs.... and repairing spark plug threaded holes:
It is not uncommon to see damaged spark plug threaded holes in the cylinder heads. This
comes from excessive torque, dirty carbone'd threads, etc. If the threads are in need of
repair, you may....or may not....be able to 'reform' them, withOUT installing a Helicoil. Some
experience & inspection with #1 eyeball, should tell you yes or no. If one EVER uses
anti-seize at a spark plug, that material can impregnate the threads, & thereafter it
is best to continue with anti-seize, & to REDUCE maximum torque. This is especially
so with aluminum, & rather less so with steel inserts; & about in the middle with
cast iron heads.
IF you find a spark plugs that, upon a SMALL AMOUNT of loosening, seems to
tighten up appreciably, STOP!!!!
Now is the time to try to avoid thread damage!! Use a lubricating penetrant. A homemade
50-50 mixture of ATF in acetone really is better than commercial penetrating oil products!!
Apply the mixture several times;...allow to soak, even overnight if need be; & then remove
the spark plug carefully to avoid damaging the threads. This means, sometimes, using a
tighten-loosen-tighten-loosen approach. Flood the threads with more penetrant if needed.
In some instances the penetrant can be used without removing the head, but be careful,
do not damage the threads by using too much removal torque;...take your time.
Snowbum heats up the head (running the engine is best for this), and then tries spark plug
removal. NO excessive torque, no matter if hot, or oiled, or anything.
How to clean up & prepare damaged threads; the head being left in place on the engine:
(if just carboned, try using hand-rotary motion on a shotgun cleaning brush)
To prevent any chips from getting into the cylinder, there are various ways. These INclude
using a lot of grease on the tap (MY method); filling the cylinder with shaving cream (must
be cleaned out later); using a vacuum cleaner in reverse to pressurize the cylinder from
the intake, exhaust valve open). ... Or, a combination of things.
If you are installing a Helicoil with the head still on the cylinder, you may want to use the
grease-on-tap method & the pressure method, both at the same time & do wear eye
protection. That usually works quite well. NOTE that it is critical that the threads be 100%
DEgreased before installing the Helicoil, & the Helicoil may be locked in place by using
Loctite RED during its installation (do NOT forget to have the Helicoil below the surface!).
Allow the RED Loctite to FULLY cure for a couple of days, then clean the threads VERY
thoroughly with a strong solvent, such as acetone or MEK, and a brush, BEFORE installing
the spark plug (treat the threads with a very thin amount of anti-seize compound)!!!
DO NOT FORGET THAT STEP OF CLEANING OFF THE EXCESS UNCURED
LOCTITE!... You do NOT want to Loctite your spark plugs into the Helicoil!
The heads get pretty hot & Loctite only gives a small amount of holding power when the
head is hot. In an emergency situation, or if you don't want to wait a few days, or?.....just
clean the threads & install the Helicoil, & ride away.
It is VERY important to have a guide machined to allow exactly 90° drilling AND a guide
machined for the the tap.. to start threads dead square to the surface, & continue with
the tool dead square. Guides should be used for both drilling & tapping. Tap handles
often have a centering recess in one end, helpful with some jobs that can lay flat....you
are unlikely to use that feature on the heads.
Here is a method to try if the threads are not too bad:
Be sure the piston is not too near being fully outwards. Take a small piece of cloth, & roll
it up to fit moderately tightly in the spark plug hole. Soak in penetrant, let sit overnight.
The next day, use a shotgun cleaning brass brush with a solvent or even the penetrant, to
clean the threads. Then use a good fresh sharp 14 mm tap that is well-greased. Keep the
tap quite squarely to the surface. Back the tap out often. Use a bit of White Lead or good
cutting compound meant for aluminum materials, on the tap during the thread reforming.
You can use anti-seize compound for this if you wish. In many instances the tap will
reform the threads, rather than cut them (it may do both). I then thoroughly clean the
threads, leaving the threads clean & dry. THEN I put a dab of anti-seize.....not much...
on the first 4 threads from the spark plug electrode tip end before installing the new spark
plug. I then torque properly. Do NOT spread a lot of antiseize onto plug threads. You want
to totally avoid getting any on the ceramic tip area, where it WILL electrically short circuit
NOTE: When doing threads or Helicoil work, be sure to have the piston down from TDC
(down from OT mark)... enough so that drills, taps, etc., will not strike the piston. Do not go
too far with this, or there will be lots more volume which takes too much shaving cream foam,
or too much air movement to blow out the chips.
There are reasons I do not recommend resistor spark plugs from ANY manufacturer for BMW
Airhead motorcycles. The main reason to use 'Resistor' plugs is to reduce the current in the
spark & leads, thereby reduce Radio Frequency Interference (RFI). A side benefit is that the
reduced current will DEcrease spark plug electrode wear.
It is possible that another reason might have been spark duration time....as resistance can
slightly increase the length of time the spark lasts, allowing better igniting of the fuel-air
mixture...up to a point, & then the energy level during part of the striking arc falls off, &
performance suffers. There are also arguments against that theory of spark (plasma)
duration; then one gets into electrical spark characteristics in some esoteric ways, so I
won't go further with that here. One final argument deals with resistors upsetting the
relationship between specified COIL secondary resistance and the spark.
There can be real problems with spark plugs that contain "resistors". I'll get into a bit later on.
Suffice it to say that a real resistor is incorporated into the stock or NGK aftermarket spark
plug resistor-type caps. Values of 1000 or 1200 ohms on early bikes with points ignition; and,
5000 ohms on some later points ignition bikes (1000 is OK for them), and ONLY 5000 ohm
caps on the electronics ignition models (1981+).
Some types of RFI can affect other things, such as electronic ignitions & electronic tachometers,
sometimes in strange ways. In our Airheads, the resistance in the plug caps have SEVERAL
functions...here are a few...more following this paragraph. (1) reduce the erosion of the
electrodes in the spark plugs. (2) RFI. (3) Protect against RFI being conducted into wiring
& thereby getting to the Hall element in the canister on 1981+ models....it can destroy that part.
(4) Interference with the tachometer.
You will find the same cautions for various reasons with such as the Boyer Microdigital ignition, etc.
If one uses resistor plugs and non-resistor caps, there is a danger that you (or someone)
might install non-resistor plugs later on, injuring your electronic ignition. If you install
both resistor plugs & resistor caps, your spark can become too weak to reliably fire the
mixture, particularly in leaner-running bikes. This has been seen with 5,000 ohm caps
& resistor spark plugs at the same time. Yes, I am aware that BMW does it on some K
bikes...but, did you know the original spec was resistor CAPS, only?
On the POINTS airheads, especially the points models with two coils before 1979, the stock caps
were about 1000 ohms in the earliest years, then later went to 5000 ohms. A change on only
points models, from 5000 back to 1000 ohms MIGHT give some extra ignition performance in
the highest rpm area...near redline+-.....& probably help in starting in cold weather; & in other
marginal situations. Thus, 1000 ohm caps are OK, in my opinion, for POINTS models. In fact,
I recommend the 1K caps for POINTS models.
The 1981+ models have more energy coming from the coil(s), & are designed for & easily handle
the 5000 ohm caps...BUT anything under 2500 ohms is likely to damage the ignition on 1981+
models. Do not misconstrue my words here. For the electronic ignition models, I recommend
the 5K caps & NOT to use resistor plugs!...although you MAY get away with using both,
without a degradation in performance.
>>>SOME 'resistor' spark plugs are not true resistor plugs...they have a small coil of wire wound
to act like an electronic 'choke' (inductor), and may be so wound to incorporate a capacitance effect
as well. The electronic ignition may NOT like it, & I can speculate about some potential problems.
That same sort of thing was done with spiral-wrapped ignition wire....sold as Suppression Wire,
where it was NOT really resistance suppression wire. You can measure the plug, if curious....
with an ohmmeter.
For those who want originality: Original type Beru metal cap spark plug caps; wires, and other
bits, assorted styles, are available from: www.euromotoelectrics.com
Bosch has been dropping the availability of NON-resistor spark plugs. I expect,
per what Bosch technical support folks have told me, that eventually you will not
be able to purchase Bosch spark plugs withOUT resistors, except, perhaps, for
awhile, from BMW bike dealers. Bosch has told me that the nominal value for
the resistors in their plugs is going to be 2000 to 6000 ohms. At this time I can
NOT recommend, & in fact I specifically caution against, using Bosch "resistor"
plugs in 1981+ models, or any models you have converted to electronic ignition.
I do NOT like to see ANY resistor plugs at all in Airheads. You COULD use
resistor plugs from Bosch if you removed the resistor spark plug caps & installed
zero ohm caps on POINTS models ONLY.
The worst thing about what Bosch is doing is that they have, purposely, or
accidentally,....SOMETIMES put these resistor plugs in the older small cardboard
boxes with wrong printing. If you purchase a Bosch spark plug (they DO make
quality plugs! ...the German made ones anyway), check the box contents...read the
number off the plug metal body itself, do NOT depend on the box numbers! NOTE
ESPECIALLY, that Bosch has gone to a 4 digit part number for plugs. There is no
good way for you to tell if the plug is a resistor type, or not, from just that number,
unless you KNOW, & especially if it is the only number ON THE PLUG. There is
more on this box problem later in this article! Your BMW bike dealership, if it
orders plugs from BMW, will probably have the non-resistor plugs, & with the old
part numbers on them....but, be sure. I am not going to try to keep up with that.
Just look at the markings on the spark plug metal body. NO R allowed in the part
number...if it is a conventional old Bosch number.
NON-projected nose spark plugs MAY foul and/or misfire. Platinum-tipped or other precious
metal tipped plugs ..very especially with more than one surrounding ground electrode ...are
a waste of money & may well NOT give reliable ignition...they can, at a minimum, occasionally
misfire & even if you don't feel it in engine performance, they can waste fuel. Single ground
electrode, projected nose, platinum-tipped plugs are OK, but a WASTE of money; there is
some indication that these 'fine electrode' platinum plugs are NOT as good as the STOCK
types. Of course, this is contrary to manufacturer's advertising....nothing new about that sort
of thing. BMW did engineering work to ensure that the incoming charge is swirled & passes
'just so' at the spark plug. Save your money, DO NOT buy specialty spark plugs, not even
those from Bosch.... but DO purchase Bosch-German or NGK standard spark plugs; NON
resistor types. Avoid Champion spark plugs, I don't like the threads I've seen on some of them.
AVOID lesser brand plugs, AVOID specialty electrode plugs.
The latest NGK Iridium spark plugs are constructed with a double shelf, or call it a tiny step
in the insulator side near the end. This offers a secondary spark area, that also cleans the
center area. PRELIMINARY tests CONFIRM NGK's claims. I have yet to do dyno tests on
any BMW bike with this type plug.
Do NOT use resistor plugs. If the part number on the spark plug body has an R in
it, it is a resistor plug. Some plug makers, including Bosch in its new numbering
system (which I dislike, they offer no information by number as to head range nor
size).... do not use that R, simply using an all numbers no letters part number, so
BEWARE! If you INSIST on using resistor plugs because you are too lazy to wait for
an order for the non-resistor types, & use the stock resistor caps, your ignition MAY
be a bit weak, but I don't see any problems beyond, MAYBE, hard starting &
occasional misfiring & wasting fuel...depending a whole bunch on engine &
electricals condition. You may not even notice any misfiring...but your fuel mileage
WILL or MIGHT suffer.
Using spark plugs that have an extended nose/tip is important for proper
combustion on an Airhead and K bike engine.
This is edited from something I posted to the K-bmw list.
Where precious metal (iridium, platinum...) spark plugs have value is on vehicles that
don't have the spark plugs replaced very often; and/or, that have quite powerful ignitions.
Years & years ago there were almost no such ignitions, & the usage of long lasting
precious metal spark plugs was for industrial pumping engines, etc. More recently,
especially in the nineties & to the present, many cars have manufacturer's recommend
plug changes as late as even 100K miles. This is primarily due to the use of UNleaded
fuels, & the exceptionally clean burning of modern uel injected engines. Many modern
cars are running somewhat higher rpm, more sparks per mile, & using very high powered
ignition systems....that can be harder on spark plug electrodes; they can erode away
faster. For these vehicles, I almost always recommend you use the manufacturer's
stated make and model of spark plug.
Those of you that no longer have or use leaded fuels, AND use FULL synthetic oils (and
in some instances part-synthetics), may well find that your spark plugs can last 50K miles
in your bike. DO NOT bend the ground electrode after use, the plugs will usually work fine
even up to even 0.040"+- gap.
Some of the new spark plugs with two grounding electrodes come pre-gapped, & the gap
is wider than your manual says to use. Leave the gap alone. Example is the plug that
BMW started specifying for the K1200 models: Bosch XLR7DC
Those can be used, in some models and situations, with non-resistor or 1K resistor caps.
In the old days, before the change to unleaded fuel in the eighties, spark plugs HAD to be
replaced around 10,000 to 15,000 miles due to leaded fuel fouling. Mechanics would often
sand-blast the plugs in a special blasting machine, and get more life. Leaded fuels are now
long gone in the USA; and, the present additives, which do deposit somewhat on the spark
plugs, are vastly less inclined to electrically foul the spark plugs. Engines are running
leaner, which means more heat, and the spark plugs are being specified to run slightly
hotter to keep deposits reasonable....all these things keep the spark plug cleaner...but eat
spark plug metal a tad faster in some situations, and in others, LESS wear. Because
modern engines are fuel-injected and burn as lean as possible and very close to optimum
at nearly all times; they need high powered ignition systems. Most cars have high
performance ignition systems.....many have separate coils for each cylinder and/or
fast rise times on the spark, and lots of Joule's (a measure of total energy in the spark).
These systems can kill. It is true that nearly all cars that don't have a coil located at each
spark plug, have series resistances in the ignition...that reduces the current & also makes
the spark have a bit better duration & spark plugs last longer. Spark duration due to
resistance effects is not totally accepted by all folks or engineering nerds.
High powered ignitions can really eat electrodes, particularly if the resistance in the circuit
is low. There are some cars that have a polarity reversing method in their ignition systems....
every other spark is reversed in polarity...this helps a small amount with erosion, but not
so good with ignition performance...unless the energy is increased...which IS done!.....the
net result IS an improvement in lowering over-all electrode wear. There are also problems
with the cars that are using one coil per two cylinders...they need increased electrical energy.
So, modern cars CAN be hard on spark plugs....and CAN, often, use precious metal-tipped
plugs to advantage:
1. The precious metal lasts longer, so gaps are more constant, erode less.
2. The precious metal plugs typically have smaller central electrode, leading to higher
temperature of the center electrode being possible with somewhat easier spark initiation.
One method of reducing the rate of constantly but slowly increasing spark gap, due to
spark/plasma erosion, is to use precious metals, which, for various reasons, do not erode
so quickly. Higher resistances, such as the use of 5K caps are also helpful in reducing
current (not voltage), which reduces metal erosion.
I see no reason to pay premium prices for an Airhead or BMW Classic K bike's spark
plugs....at least not for Iridium or Platinum tips. BUT...if you are going to try for 50,000
miles on your plugs, you might be interested in trying them. Some of the fine wire spark
plugs have another feature that is hard to describe. NGK has been at the forefront on this.
The insulator at the tip has a taper and a L shelf. This can improve the performance. It
is hard to do this with a large size central tip, so these are fine-wire precious metal spark
plugs. They work well in K bikes.
There ARE reasons to use certain types of spark plugs. In a Service Information Bulletin
for the K1200, BMW went from the recommended Bosch XR5DC (Earliest prior K models
had X5D, then X5DC, and then XR5D) to a dual ground electrode type XR7LDC. The
XR7LDC has been adopted by many BMW dealerships for prior K models. The two
spark plugs have seemingly equivalent heat ranges in practice (in the K BIKE), ....so never
mind the 5 versus 7 here. I do think the 7 is SLIGHTLY hotter, by MAYBE half a step, in
practice. This thin center & dual grounding electrode plug lasts longer, offers slightly better
ignition under some types of conditions....so goes the theory. Many will substitute NGK
or other plugs, some are listed in the K bike section well below, and these have been
substituted quite successfully, that are conventional electrode; for the somewhat special
K bike plugs used on some models. That they MIGHT be wasting a teeny bit of fuel is not
noticeable to them. I am not sure they ARE wasting fuel, as it is difficult to measure.
The in-expensive 4163 spark plug is an example of this substituting.
The XR7LDC comes pre-set for gap. It is wider than you are used to.
Do not change the gap!!! DOES NOT FIT AIRHEADS.
There is a LOT of snake oil hype regarding spark plugs. Do NOT carry over my dual
grounding electrode remarks to include all other engines. It is a KNOWN fact that the
type of combustion chamber coupled with the intake mixture direction, on the
AIRHEADS, is such that a dual electrode spark plug is WORSE than the stock
single electrode. This has to do with the pathway of the mixture to and through/over
the spark plug gap area. The so-called split tail or dual grounding electrode
plugs that are hyped, SplitFire, and others, are NOT of ANY help. Worse ....for
Airheads...are the multiple grounding electrode shrouded centers...almost always MUCH
WORSE than stock. I have removed multiple shrouded plugs (EVEN Bosch +4 Platinum's)
from Airheads because they work lousily....& I can quote other examples.
NOTE: A technique called INDEXING is often used in RACING (and a FEW stock
cars too, like the Honda Insight), for various purposes, including reducing metal-to-metal
interference in very high compression ratio engines, & to point the gap at the intake valve,
supposedly this will help with initiating rich mixtures, etc. Yes, it helps. No, it does not help
on stock or near stock Classic K bikes and similarly stock or near stock Airheads.
The bottom line, for AIRHEAD owners, with stock or near stock engines (increased
compression ratio or dual plugs is considered near stock by ME), is to use single ground
electrode, extended nose spark plugs, & use of the cheaper larger center electrode plugs
NOTE: As noted earlier....on Airhead dual-plugged heads... it is somewhat common to
use a lower spark plug that is one heat range step hotter, as for various reasons the
lower spark plug may otherwise tend to carbon-up faster.
VERY OLD Bosch numbers:
Bosch made these spark plugs, used on some bikes:
W240T1 was 1/2" reach, 14 mm threads, same as later W4AC. This plug was used
on the BMW singles & a few pre-Airhead twins. The 3/4" reach, 14 mm
threads version of this plug was used on those twins that took 3/4" reach
spark plugs; typical numbers were W3CC; W4CC; W5CC.
W240R2 was 3/4" reach, same as later W4C2
W260T1 was 1/2" reach, same as W3A1
W260T2 was 3/4" reach, same as later W4C1.
After so many years there is confusion over how these plugs were numbered & identified.
The above is the best information I have at the moment....but, see the CHART below.
Bosch no longer has the very old type numbers in their catalogs. Bosch has recently
transitioned even their recent plugs to 4 digit numbers, see the chart below.
In the plugs like the W230T30, as the "230" went higher in number, the plug got COLDER.
Exactly the opposite of the newer Bosch W numbers in the chart below.
Equivalents, Bosch, NGK, etc:
(Snowbum has charts crossing over almost every make of spark plug, even old English
types, even back into the 1920's...).
Bosch Plugs with 'BC' are the 1/2" reach for BOTTOM plugs in those dual-plugged
bikes that take 14 mm size and not metal-added; 'DC' are 3/4" reach for top plugs.
Sometimes spark plugs from one manufacturer are in-between a heat range of another
manufacturer, or have a slightly wider heat range capability;....thus you see the Bosch
6 & 7 series being covered by the NGK 6 series.
Warning!.....Bosch WR plugs (not recommended for airheads) may have the wrong
gaps for airheads! Check the gaps! Bosch plugs beginning with WR are resistor
plugs!! They are not directly interchangeable with the spark plugs not having the
"R"...no matter what Bosch or a salesman says!
WARNING!....Bosch plugs with a + sign at the ending MIGHT really be resistor plugs!!...
even if the part number does NOT have an R in it!!
Spark plug heat ranges are not 'exact' oftentimes when trying to cross one
manufacturer's number with another. Complicating this is that spark plugs were
improved over the years, & a single part number may now cover an actual slightly
wider heat range.
See the 'comments' column; and, the various notes in RED.
Do NOT use resistor plugs. If the part number on the spark plug body has an R
in it, it is a resistor plug. Some plug makers, including Bosch in its new numbering
system (which I dislike, they offer no information by number as to head range nor
size).... do not use that R, simply using an all numbers no letters part number, so
BEWARE! If you INSIST on using resistor plugs because you are too lazy to wait for
an order for the non-resistor types, & use the stock resistor caps, your ignition
MAY be a bit weak, but I don't see any problems beyond, MAYBE, hard starting &
occasional misfiring & wasting fuel...depending a whole bunch on engine &
electricals condition. You may not even notice any misfiring...but your fuel
mileage WILL or MIGHT suffer.
Bosch number series
|NGK with removable nut||NGK withOUT removable nut||
|W5D||W5DC||7591||BP7ES||1034||3995||W5 covers both W225T30 and the colder W230T30. BMW part number 12-12-1-338-146; BE SURE if purchasing from BMW dealership or independent, that the plug is NOT WR5DC|
|4007||Champion N-9YC can work OK, if you cannot find NGK or the part from BMW. BMW part number 12-12-1-338-145; BE SURE if purchasing from BMW dealership or independent, that the plug is NOT WR6DC|
|W175T30||W7D||W7DC||7500||BP6ES||7333||4007||BMW sold the Bosch W7DC as number 12-12-1-267-485. May be found as 12-12-9-062-594. BE SURE if purchasing from BMW dealership or independent, that the plug is NOT WR7DC. Some time ago, the Beru 14/7DU was available as BMW number 12-12-1-265-595. BMW also sold the Champion equivalent as 12-12-1-338-147.|
Higher numbers are colder. That is, W230 is colder than a W175.
Higher numbers are hotter
Bosch plugs above ending in C cover a slightly wider heat range than the non-C and early Bosch to the left. Higher numbers are HOTTER
Be careful with these types of numbers, as you want to be SURE the ACTUAL spark plug, for your Airhead, no matter what the carton has printed on it, is a NON-resistor. See note in paragraph after this chart.
Higher numbers are COLDER
|BMW dealerships & Independents may carry the NON-resistor Bosch Spark Plugs. See the notes, above. Be sure that you do NOT get the WR..... spark plugs, which have resistors.|
Bosch has, on occasion, put their
resistor plugs in the small cardboard boxes that are marked for
the non-resistor plugs. Also reported to me was that the number on the box for non-resistor used to
start as 0-241-; and Bosch MAY be putting resistor plugs into those boxes, with the boxes showing 0-242-.
My answer to this is to NOT trust what the box says...open it and see what is printed on the plug base
metal. I'm anal enough to use an ohmmeter on the center electrode!
Here is an enlarged picture showing what one Bosch box end looks like. Do not trust anything on that
box end...look at the markings on the plug metal itself. You might find this box contains a resistor plug.
Airheads spark plug gaps:
Gapping brand-new plugs for Airheads, these plugs have been NEVER EVER RUN, use 0.6 mm,
0.024" (preferred); ...to 0.7 mm, 0.028".
If they need gap setting, be very careful not to damage the central insulator. The place to put the
bending pressure is close to the central electrode/insulator, but do NOT pressure the white
insulator. Plug gap will open up as the miles accumulate & the ground electrode will dish a bit.
Erosion/Dishing can be at the center electrode if the ignition coils are wrongly connected.
Once worn, the gap should be measured with a ROUND WIRE gauge. My quite old
recommendation was that if plug is worn to over over 0.8 mm (0.032"), to throw them away.
Part of that recommendation was that leaded-fuels were in use. With unleaded fuels I now
think that wear up to 0.040", and possibly a bit more, is OK.
I am aware that some books say to use or set gaps to 0.7 mm (0.028") & some literature say
that up to 0.9 mm is OK for late eighties to 1995. DO NOT gap-set previously run spark plugs.
Due to leaded gasoline having gone bye-bye, spark plugs will last a lot longer than they used to.
In the leaded gas days, spark plugs in a clean burning engine would last 15K-20K at very best.
Double that is pretty common these days for Airheads, & some have gone 60K. I am OK with
running spark plugs for as long as they work well; PROVIDING that the gap has not worn too
far (not over .040" generally, but perhaps slightly more); & the ground electrode is NOT
****Once a spark plug has been in an engine and run ...EVER, ... DO NOT EVER adjust the gap.
The reason is that ground electrodes in the spark plugs change their metal structure once
heated; bending them can weaken them; there is a possibility, although this is quite rare, that
the electrode will break off & damage the engine.
Spark Plugs for Classic K bikes (K1, K75, K100, K1100, all versions of these models):
(you can add K1200 here too, see text above, well above, and here)
These bikes use a 12 mm 3/4" reach spark plug.
These are 5/8" or 11/16" hex depending on whose plug you use. Keep THAT in mind as
you might have only one spark plug wrench size, & a larger size may not fit well
considering the size of the 'casting hole area' around the spark plug.
The spark plugs used on the Classic K bikes were specified, depending on the year of
the manual, BMW SI's, etc, as: X5D; X5DC; XR5DC, and XR7LDC which was the last
update, and actually was for the K1200, but is applicable to the earlier K models. The
XR7LDC has a dual grounding electrode. "R" in a plug number means it is a resistor
type. BMW K bikes had 5KΩ spark plug caps. The K75 bikes had a GAP in the spark
plug lead, thus cannot be as easily measured for the spark plug cap resistance.
Except for the XR7LDC, the plugs should be gapped (bend the ground electrode ONLY
if the plug is 100% brand-new, never run in an engine) at 0.6-0.7 mm (0.024"-0.028").
The XR7LDC comes pre-gapped, wider than that just mentioned. Do NOT change its
gap. Be a bit cautious about what you may think you know about heat ranges. An
example is that the XR7LDC is nearly the same heat range as a XR5DC, in actual
use IN THE K BIKE.
It is perfectly OK to use NON-resistor X5D or X5DC spark plugs.
NGK makes a 12 mm, 3/4" reach, 5/8" hex, sparkplug. Model DCPR7E, new number
3932, has removable terminals, tapered, shelf'd insulator, unsure of gap they come with.
It supposedly is a substitute for the DR7EIX, a fine wire iridium plug, #5686, that is
substituted for the Bosch XR7LDC; the TIP lasts longer.
NO TESTING INFORMATION BY ME YET.
NGK equivalents such as the D7EA (7912) and DR7EA (7839) work fine in BMW
There is absolutely nothing wrong with using the original non-resistor, large electrode,
inexpensive type of spark plugs in a Classic K bike!!! The electronics is protected
by the 5000 ohm spark plug caps.
Another spark plug that has been proven to work well, and is INexpensive, is the
When installing rubber covers (boots) over the spark plug wires where they
fit over the neck of the spark plug caps, lightly coat the inside of the rubber
cover with silicone dielectric grease. Do not use the stuff on the electric
contacts or contacting area. Use it on the RUBBER. This caution applies to
the rubber cover (boots) at the spark plug cap, and to the rubber boot at the
coils. If the coil electrical fitting end of the wire is tight-fitting into the coil
internal metal contact, it may not cause a problem, but do it correctly anyway.
The application will make removing the boots easier, and prevent electrical
contact corrosion from the elements, etc. You can coat the spark plug white
outer area a bit too.
https://en.wikipedia.org/wiki/Spark_plug Lots of information, explained differently,
Reference information: http://www.ngksparkplugs.com/docs/resistor_covers.pdf
covers the below information and more.
Below is a chart on NGK spark plug
caps, which are very popular with the Airhead
community. Very commonly available is the LB01EP and LB01F; and LB05 series.
LB01E new number 8011
LB01EP new number 8328
LB05E new number 8031
LB05EP new number 8020
LB05FP new number 8030
LB05F new number 8051
Here is a link to NGK's article on the caps & wire assemblies.
It is much more detailed than the above:
NOTE! You will likely NOT find all those NGK spark plug cap models available to
you. The most common type available is the LB01 and LB05 type. Note carefully
before you purchase ANY, as to the next letter following. That is, note the E and F
above. STOCK BMW spark plug wires come with caps that have varied in style
(some are metal covered, some fully molded, etc, and caps have varied from a
nominal 1000 ohms or 5000 ohms)....but one thing is common to ALL the STOCK
BMW Airhead caps: they are designed to fit onto the THREADED post of the
spark plug. There ARE spark plugs that do NOT have removable threaded caps,
so watch out for those too. Be sure that whatever spark plug cap you use is
compatible to the spark plug itself. Take into consideration that you might be using
some sort of shorting device or adaptor when synchronizing carburetors, so that is
also a consideration if you should change your type of plug or cap type. NGK spark
plug caps last a long time.... AND, I have almost never seen a failure of the resistor
element inside them.
04/22/2003: clarifications and emphasis here and there.
08/09/2003: edit for clarity
08/13/2004: minor editing for additional clarity, including more detailed information
on previously anti-seized threads.
09/13/2005: Add section on resistor plugs and wires, etc.
01/11/2007: update with latest information, and add the NGK chart
03/25/2007: add equivalents, Bosch and NGK
03/27/2007: Rearrange order of last items on page, add more information on the
Bosch Plugs problems.
09/16/2007: Clean up
01/06/2008: remove bad hyperlink to old Bosch plugs at automotive-tradition.de
01/15/2008: Totally revise the article, combining information on holes, etc., from
Engine Internals, ETC.
10/01/2008: add section expanding on special spark plugs
11/09/2008: add OLD Bosch numbers section
01/18/2010: go through entire article, improve clarity; fix errors, clean up emphasis
10/30/2010: Add new NGK numbers
10/31/2010: Clean up article somewhat and add final note to the NGK information, in red.
01/01/2011: Add really old Bosch numbers
04/25/2011: Add photo and description of the three plugs at the top of the page.
01/01/2012: Add Euromotoelectics link
02/16/2012: expand warnings about regapping.
03/31/2012: Revise article, make table of equivalents, etc. NO errors were found nor
corrected on prior version.
undated, 2012: remove indexing section.
04/01/2012: Clean up more of article. Clarify that it is the exhaust valve, not both, that
are to be open if not removing head for insert installation.
04/03/2012: A bit more work on the table-chart, and eliminate duplications earlier.
04/07/2012: Add more information on NGK spark plugs to the table-chart.
10/14/2012: Add QR code, add language button, update Google Ad-Sense code
12/10/2012: Clean up article a fair amount. Add Airhead gapping information in detail.
sometime in 2013: Remove language button; coding was causing problems with SOME browsers.
03/14/2013: Much deeper into the controversy over using, or not, antiseize compounds. This was
added as few understand that I have REAL data, & REAL industry information, that
is not, seemingly, read by those who have FAULTY ideas on the subject.
09/17/2014: clean up article, mostly for use with smaller screens.
02/04/2015: Clean up article once more, nothing substantial changed in values/methods.
08/23/2015: 0716 Pcst time. Release two updates, combined, since March.
11/13/2-15: Clean up article presentation. Meta updates. Add more comments to the chart on
spark plugs, etc.
12/15/2015: Final meta-data fix. Clean up article, justifying to left, etc., for better presentation
on smaller devices.
12/16/2015: Clarify BMW part numbers and Bosch cautions. Wasn't any errors.
12/25/2015: Minor clarifications about torque values
© Copyright, 2013, R. Fleischer
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