FLYWHEEL REMOVAL-REPLACEMENT WARNING!!!
© Copyright, 2014, R. Fleischer
Article 60, sub-section 2
This is CRITICAL!
...so Flywheel Removal/Replacement is the first item here!!
There are potential trouble areas when removing & replacing a flywheel (or, from 1980,
called the Clutch Carrier). First trouble area is the moving of the INNER thrust washer
off its pegs, which YOU WILL PREVENT by the use of a crankshaft blocking tool, information
later herein (with a photo). There is a second thrust washer. The REAR thrust washer,
similar to the front one, can come off its locating pegs. It must be on its pegs, and not be
rotatable by your fingers (check!) before you reinstall the flywheel. Sometimes the pegs
do not stick rearward very much. You can use a very thin amount of a soft grease to
'stick' the rear thrust washer to the boss/pins. Thrust washers are listed in parts catalogs
by that name, & also by such names as stop discs, thrust discs, or stop rings.
When you remove your flywheel (for such as to replace a main seal, oil pump seal, etc.), it is
CRITICAL that the crankshaft be BLOCKED from moving forward. This blocking is often
done by some sort of makeshift tool that places some pressure against the alternator rotor
center bolt. This can be done in many ways, such as a piece of 2 x 4 lumber bungeed to the
cylinders or exhaust pipes; with a screw to press against the rotor bolt. Very crude, that.
A small easy-to-make tool can be made of a piece of Allen wrench with a welded or brazed
fender washer on one end, over-all about 3/4 inch long. The outer cover holds it in place,
the tool being made just a bit too long to allow the cover to fully bolt-up to the engine; this
gives a bit of pressure (do NOT but BARELY tighten the cover bolts!!). The tool's Allen end
simply fits into the existing alternator rotor bolt head. I recommend you make one of these
small tools the way I designed it. You can also just use an 8 mm bolt, screwed into the rotor,
leaving enough of the bolt forwards, so that the front cover will bear on it.
If you do NOT block the crankshaft, there is a REAL RISK of the crankshaft moving forward a
small amount. Very little movement will cause the HIDDEN thrust washer to move off its pegs.
The thrust washer will not be aligned on those pegs as you tighten the flywheel bolts (you
do not have to tighten very much to cause damage). HUGE RISK of MAJOR DAMAGE to the
thrust washer....AND you may even damage OR RUIN the engine casting!
With a thrust washer having fallen off its pegs, you will find that the crankshaft will essentially
freeze up as you tighten those bolts. You REALLY DO NOT want this happening!! You do NOT
want to even get near the point of the crank freezing up. If you forgot or did not know about
blocking the crankshaft, & you want to know IF the crankshaft has moved, the sketch, well below,
will give you the information. If you have ruined a REAR thrust washer, that is NOT a disaster
(assuming you did not injure the bosses area). You just need another thrust washer of the
SAME COLOR identification. Sizes are also listed in the literature.
If you have blocked the crankshaft before unfastening the flywheel bolts, you have nothing to
worry about, regarding the crank moving & the forward thrust washer dropping! You must be
careful about the rear one coming off its pegs, when you re-install the flywheel.
The only way to see & get to (however slightly) & MAYBE get the forward thrust washer back
in place if it has moved off the pegs, is either by removal of the right cylinder.....or disassembling
the engine (totally!). Do NOT think that you can tighten the flywheel bolts to see if the crank
will start to seize up; that is, if engine rotation becomes more difficult. By the time the crank
gets to that point, you already have likely caused damage. If you think you may have goofed,
take the measurements!
If the forward thrust washer has already been destroyed/damaged, then disassembling the
entire engine is your only option. This is very serious business, with many additional
ramifications not mentioned here. So, heed my words, heed this article!! BLOCK THE CRANK!!
YES, I am WELL AWARE that many have never had a problem from not blocking the crankshaft.
PLEASE heed MY cautions; DO block your crankshaft.
Snowbum's Tool to hold crankshaft from moving forward:
NOTE: If you remove your flywheel for any reason, be sure to FIRST set the engine to OT, top dead
center, Oberer Totpunkt, and be sure that OT is STILL in the timing window when replacing the flywheel.
Make the tool out of a piece of 6 mm Allen wrench material. Weld a steel disc or 'fender washer', perhaps
one of 1 inch in diameter, onto one end of the cut piece of allen wrench material. The washer should be
maybe 1/16" thick (not critical, no harm with thicker). Make the length such that the Allen end fits FULLY
into the alternator bolt, & the disc end presses against the inner surface of the timing chest cover.
Usually ~3/4 inch overall. The length should be such that there can be some light pressure is applied by
the cover when the cover is screwed back onto the engine LIGHTLY, but the cover can't be brought back
fully to the engine surface. DO NOT over-tighten. Weld the washer squarely to the straight piece of 6 mm
Allen wrench. The last time I made one of these, I made it to fit my 83-84 bikes; the OVERALL length
was 3/4". You can also just use an appropriate length of 8 mm bolt in place of the rotor bolt, and not have
to make this tool. Some have just used a piece of allen wrench. Carry it in the tool tray on the bike, but you
are UNlikely to ever need it while touring.
NOTE: If you remove your flywheel for any reason, be sure to FIRST set the engine to OT, top dead center,
Oberer Totpunkt, and be sure that OT is STILL in the timing window when replacing the flywheel.
Below is a sketch of the flywheel and crankshaft of your Airhead.
Following this section is information
on main seals, etc.
Dimension B is the depth of the flywheel (or clutch carrier, as it is called on 1981+ models) where the
crankshaft boss fits into. The sketch is simplified, and does not show how the rear thrust washer is
retained, that the 'pin' is proud-of, and fits into the thrust washers....and other such minor details that are
of small importance here.
Another way of explaining things: A must be greater than B by at least .05 mm. If A is LESS than B, by,
perhaps, 3 or 4 mm, then the crank has moved forward; the thrust washer has slipped. If you triey to
bolt-up the flywheel, serious damage will occur. If the amount of forward movement is quite small,
you may be able to move the crankshaft backwards with some relatively modest pressure at the alternator
rotor. This might also be done by bolting up the flywheel to the crankshaft VERY LOOSELY & moving the
flywheel rearward by hand pressure. If you can move the crank by either method to the proper dimensions,
A is larger than B, you have 'lucked-out', & you can tighten up the crank to torque specifications & the
crankshaft will not be locked up. Be really careful!
This original sketch was done by Tom Cutter who furnished it to me as I was too lazy to
make one. That sketch was improved for clarity for me by Peter Holdcroft in July 2012.
Things look a little bit different for the clutch carrier models (1981+), but you will be able
to see if there is a problem by taking the measurements. I cannot emphasize enough
how much I recommend you BLOCK THE CRANKSHAFT, by one of the methods
outlined earlier in this article......thereby totally avoiding any problem...and you certainly
will have no need to take these measurements.
Flywheel bolt torques
This is in reference to a BMW Service Information bulletin (we call them SI's), dated
November 1991, #11-049-91, sub number 2495, & this can also be seen on the 12/92 fiche
on page 3, G23. In brief, it stated that while the flywheel bolts were previously at ~75
foot-pounds (100 Nm), they were now to be at 90 foot-pounds (125 Nm),... first you
cleaned the threads,... and then the threads were to be OILED! BMW specifically said
that the bolt limits would NOT reach their limit of elasticity at that torque, and could
be REUSED! I personally get more than a bit nervous, at 90 foot pounds & oiled, so I
will NOT tighten them that tight. However, some do; I have heard of no problems reported.
It is YOUR CHOICE. NOTE that this is in regards to the 11 mm bolts....certainly not to the
smaller /5 & early /6 10 mm bolts. These early bike 10 mm bolts need replacement upon
each use, which the 11 mm do not (unless overtorqued). Those 10 mm bolts in the /5
and early /6 are absolutely not be torqued to such high values. There have been a lot of
different specifications on flywheel bolts over the years. There were also two lengths
of 10 mm bolts used.
I use (clean and dry) torques of 42-45 foot-pounds on the 1973 and earlier engines;
for the 1974 I use 52-55 ftlbs; for 1975 and later models I use about 75 to 80 ftlbs. I am OK
with the bolts being faintly oily. Some aftermarket literature will show different flywheel
bolt torques for different engine sizes for the same year. DISREGARD such advice.
The big difference is in the size of the bolts, with the earlier 10 mm bolts as used on the
/5 and into early /6, using substantially less torque.
For additional details.....read the section on flywheel bolts:
Crankshaft rear main seal:
Repeated Note: If you remove your flywheel for any reason, be sure to FIRST set the engine to OT,
top dead center, Oberer Totpunkt, and be sure that OT is STILL in the timing window when
replacing the flywheel; that you have not rotated the crankshaft.
BE SURE you block the flywheel!!
Crankshaft main seals came in a number of styles over the years. The very latest seal, of a Teflon-like
material, is quite different in design from the early seals. The latest type is 11-11-1-338-342.
***NOTE: A type of geese-honking noise can sometimes be heard on an engine with the old style
seals. This noise comes from the slight vacuum created in the crankcase as the pistons go
OUTWARDS, and the atmospheric pressure, being higher, in the clutch area, pushes air into the
engine. The biggest problem is NOT THE NOISE; but that clutch dust, which is abrasive, moves
through that seal, slowly eating it away. This is not good for the rear of the engine, let alone anyplace
else the grit gets into. It primarily happens on old worn seals, even if not yet leaking oil.
CHANGE THAT SEAL!
Early seals were very conventional looking, a white colored lipped rubber seal (there have been more
than one type of lip and seal color) with a coiled spring backup. For the /6 and later, BMW ADDED
an O-ring in the flywheel bore. For the /7 and later BMW added a metal cap ("Guide Ring"),
and the O-ring is inside. In 1981, BMW changed the design of the flywheel/clutch, for lighter weight
which gave faster engine acceleration and deceleration, unfortunately with more vibration, but also
gave greatly reduced clutch hand lever pressure; the primary original purpose (Guessing). The
flywheel was now called a clutch carrier. The earlier heavier flywheel had the main seal lip resting on
the flywheel boss, so when the flywheel was inserted into the engine, the seal curled...well, sort of...
ever so slightly inward. For those earlier designs, I have recommended that the flywheel seal area be
laboriously polished with ONLY crocus cloth (in kerosene). Crocus cloth is a super-fine-grit polishing
paper. Absolutely no fingernail felt irregularities are allowed in the flywheel sealing area...although
discoloration is normal. All seals before the latest Teflon type, 11-11-1-338-342, were installed
slightly different or controlled depths to avoid old rubbed areas.
Main Seals must be installed squarely. Main Seals often fit very tightly, & you might have
problems trying to get them into their cavity. It REALLY DOES help to warm the engine
case up, considerably, in the main seal area; and this can take quite awhile. Lightly oil
the seal just before you install it. Install it squarely...it must be installed straight & square.
The cap, or "guide ring", used on the 1981+ models (the clutch carrier fits to it, the guide ring is over
the crankshaft) and has a center lug to enable it to be pulled rearward by a factory tool. To replace a
main seal on a 1981 and later, you have to remove the guide ring first. You can improvise. You can
use a flat punch to rotate the ring until some of each crankshaft hole is covered, then pry to the rear....
use a small screwdriver or similar, pry a bit on each hole/guide ring. Be careful, not to damage the
guide ring nor the threads. Once the guide ring is out, you can remove the main seal. The
Guide Ring can deteriorate (hard coating). If the surface appears to be deteriorating, that
surface could have teeny imperfections that would eventually tear-up a new main seal.
Replace the Guide Ring if it has so deteriorated
With the guide ring removed, you then install the new-style main seal. The guide ring (with a new O-ring!)
is then moved into the main seal, using the carrier bolts. When using the bolts for that, you may need to
use spacers under the bolt heads....see the guide ring installation photos, later here, showing the bolts
with some sort of junk-box provided spacers under them, to allow the bolt heads to be turned properly.
As the guide ring is installed, it makes the "Teflon-like" seal working part move forward. That helps
the seal maintain oil integrity as crankcase pressures increase during engine operation.
Leaks that seem to be the rear crankshaft seal could actually be that rubber O-ring. However,
determining which is which may not be so simple, so most just replace both mainseal & O-ring.
****Main seals are usually installed using the special factory tool, but if you are careful, you can do this
with a prepared block of wood (or Ed Korn's OR SIMILAR tool). Install the seal absolutely straight &
square. While I think ONLY the latest seals type should be used, which is installed to full depth,
if you have an older style seal you are installing, you would install at the same original depth...
except that early flywheels with a big radius are best installed not quite fully...maybe a mm will
be proud of the surface. See notes below.
Here is a link to a pdf file on this website that has the factory information on the new style seals:
MORE on the new style seal:
The latest 11-11-1-338-342 seal is a "Teflon-like" (PTFE) seal. NOTE that it is designed so if
you install it squarely, you can install it fully, without bothering about setting the depth.
There area two types of flywheel (or clutch carriers) in use. If the front end has a small radius,
then the seal is installed to full depth. If there is a taper, as on early flywheels, then the seal
is rearward a small amount, about 1 or 1-1/2 mm. Oak uses rear ring gear shims for that,
installing the shims, then the seal. I don't....because I don't have any stock of them anymore.
Hints: The latest version needs no oil soaking; but it is best to install it oiled or lightly greased
a bit for ease of installation. Using a very fine sandpaper, sand the aluminum entrance edge
to the bore in the case to allow the seal to press-in easily. Oil slightly (or lightly grease),
the bore area of the engine case that the seal fits into and the seal outer too. If you heat the
engine case around the prepared seal bore area, then add a tad of grease or oil, the seal
will press-in easier.
While you do NOT have to do this, I do:
soak the new seal & installation tool in 150°F +-
engine oil for a few minutes....the warmth helps prepare the seal, perhaps softening it.
If you have an earlier new seal (are there any still around?...I suggest you toss it and use
the new seal.
If you fail to oil or grease the new seal during assembly, it may squeak for a short while after
engine start, until oil works its way to the seal. Press the new seal in squarely, using a flat
plate seal installation tool, or fashion something. Install the flywheel (carrier) with a bit of
oil on the nose.
There area two types of flywheel (or clutch carriers) in use. If the front end has a small
radius, then the seal is installed to full depth. If there is a taper, as on early flywheels, then
the seal is rearward a small amount, about 1 or 1-1/2 mm. Oak uses rear ring gear shims for
that, installing the shims, then the seal.
****Oak did an article on main seal installation in the MAY 2004 issue of AIRMAIL (see page 17-18)...
where he discusses this in some depth, in response to a question posed by someone. ****
Be sure the 5 holes in the guide ring are exactly aligned with the crank holes, as you do this job.
If you use one of the plates-type of installation tools, you do not tighten the bolts very much.
Some recommend installing the flywheel when it has been heated fairly hot. When you align a 'flywheel'
to the crankshaft, install by eyeball first. YOU SHOULD HAVE previously set the pistons fully outward;
and now when you reinstall the flywheel, its OT mark is in the timing window when you've double checked
the pistons are fully out on the pistons. Then insert the bolts lightly finger tightened, & then find the centering
point of the assembly, by moving the flywheel CW & CCW, back & forth (mounted loosely by the bolts...
there will usually be a very slight amount of play. Then tighten to only a few foot-pounds, evenly,
cross-pattern as best you can. If the flywheel was not heated, tighten fully to specifications at this point,
in a cross-pattern. If the flywheel WAS heated, wait until it has cooled, then tighten fully to specifications.
Mind the torque. As noted previously, the early 10mm bolts must be new. The 11 mm ones are reusable,
unless damaged from over-torquing, etc.
A tool can be fashioned to lock the flywheel/carrier, while the bolts are torqued. Such tools
are shown in photos in such as Clymer's and Haynes manuals, BMW literature, ETC. The
original BMW tool may even be available, but the tool is quite simple. I recommend you do
not lock the flywheel/carrier by using the starter teeth.
Main Seal installation tools (if you decide to use them):
The original BMW main seal installation tool was #880.
There is an article on making a fancy, nice, main seal tool that works fine with the later seals.
The article is here:
In the photo below, note that the BMW stepped plate can be used upside down for flush seals,
or with the step to the inside for installing to slightly forward of flush. The Ed Korn type tool
shown uses setscrews to adjust the depth; the tool seller provides instructions with the tool.
There area two types of flywheel (or clutch carriers) in use. If the front end has a small radius,
then the seal is installed to full depth. If there is a taper, as on early flywheels, then the seal is
rearward a small amount, about 1 or 1-1/2 mm. Oak uses rear ring gear shims for that, installing
the shims, then the seal. I don't....because I don't have any stock of them.
Thanks to Al Patton for supplying the original photos of a later type Airhead (has the Guide Ring),
which I have modified & placed below.
NOTE the thrust washer & pegs!
5 bolt holes in the crankshaft,
symmetrically arranged. That is
why you MUST align the
flywheel/carrier for OT mark
with pistons fully outwards!
Note the spacers used by Al
Patton here...otherwise the
bolts would not turn at the
Note holes all lined-up
The 10 mm hex bolts at the
oil pump cover are later types.
NO need to tighten much!
|When installing the flywheel, mind information early in this article on bolts & their torques! If flywheel bolts loosen, or come out or are sheared off, considerable damage to the threaded holes can occur. This most often was seen on the old /5 bikes, with the smaller threaded bolts, with someone forgetting they were on a German bike, & shifting the wrong way, from, let us say, 2nd, with lots of rpm, down to first.
That sheared the bolts. I've fixed a few of those!!
|If you are removing the clutch (obviously needed if removing the flywheel), MARK the position of the major parts to each other, except the clutch diaphragm spring. Factory marks are at 120°.|
NOTE: If you remove your flywheel for any reason, FIRST
set the engine to OT, top dead center, Oberer Totpunkt, and be sure that OT is STILL in the timing window, or very close to it, when replacing the flywheel. Pistons are fully outwards, or very close to that.
|If the flywheel has a groove (it will if it is 10/1975 or later), it needs an o-ring there. It was 11-22-1-337-099, now is -093. A long time ago the number was 11-22-1-263-798. The O-ring is called a Seal Ring by BMW. It is 59 mm x 3 mm.|
Suppose the engine rotated some, or you forgot to mark things...or, the flywheel or clutch carrier
was mis-positioned by a previous owner. How do you find the proper flywheel position?
The safest method is probably this:
1. Remove the valve cover on left cylinder. Remove left & right cylinder spark plugs; engine is easy to rotate.
2. Place the flywheel into any bolt-hole positioning, putting in a few bolts, fully home & lightly tightened.
Remove the crankshaft stop tool only after the flywheel is in place & those bolts lightly tightened!!!
If your crankshaft stop tool (typically located at the alternator bolt, used with front cover, or other means)
is of the type that allows the crank to turn, then you need not remove that tool.
3. Rotate the flywheel slowly in the NORMAL direction, which is CLOCKWISE as you face the flywheel from
the rear. Shine a flashlight into the spark plug hole. You will see the piston come fully out, then reverse.
4. Rotate the flywheel slightly back & forth, CW & CCW, until piston is seen to be fully outwards.
Some might use a round tip metal rod for 'feeling' the piston, if so, Do NOT bugger-up the spark plug hole
edges. Rotate back & forth, etc., SLOWLY/SLIGHTLY. Do NOT use a pencil, it could break.
5. With the piston now fully outward, if the OT mark is not someplace IN the timing window, RE-INSTALL THE
CRANK STOP (see #1, if tool is already left in-place). With tool in place, it is now safe to remove the
flywheel & rotate its position so OT is in the timing hole window, or very close to that window opening.
6. At this point you probably have everything ready to tighten, in some sort of cross-pattern, the flywheel bolts.
Oil pump and oil pump cover:
The oil pump inner rotor INNER EDGE is chamfered, in case you remove it & wonder what direction
to replace it in. Another way is that the punch marks go to the rear. You do not have to line up the
punch marks. Oil pump clearances are easily measured with common feeler gauges & a machinist's
or other straight edge rule, on edge. Here are some general specifications:
Rotor 2.22" +0-.0009"
Housing 2.23" +.0017" -0
Rotor end clearance .004-.007"
Rotor thickness .54" -.0066+.0013"
Rotor to housing face .001" to .0023"
Rotor to rotor clearance .0046" to .0117"
The oil pump cover O-ring may be replaced any time the flywheel is removed. Original oil pump O-ring
was black 11-41-1-250-274, 0.079" thick. That part was discontinued a long time ago in favor of a red
O-ring that is slightly thicker, at 0.084", part 11-41-1-335-895. SOME parts lists & on-line fiche, will show
it as 11-41-1-335-896.
Early oil pump covers had Phillips screws, which often are a problem to remove (use of the special impact
wrench listed in my http://bmwmotorcycletech.info/tools.htm article is highly suggested!). Early pump
covers had tapered screw holes to accommodate the flat head Phillips screws. Early pump covers did
not seal well; the later type cover ALSO fixes that potential problem, by groove depth & later
thicker O-ring. If you have a Phillips-screw type of cover, I recommend you install the later pump cover,
with the later hex-head bolts. When installing the pump cover with its new O-ring grease the O-ring, or
otherwise be very careful that the O-ring stays in place during the installation/tightening process. I use
Loctite BLUE on the bolt threads. I am careful to tighten the 4 bolts evenly, in a cross-pattern, a bit at a
time, until tight....88 INCH-pounds (that is only 7.3 footpounds).
When setting up a lower end, particularly if it is a NEW crankshaft, you must use BMW specifications for
matching the crank color code; main bearing bushings; bearing cap (front main bearing holder). Generally,
it is a matter of matching color codes on these things...the Factory Manual has the various specifications.
If unsure, for the final word, ask on the Airheads List, rather than use Haynes or Clymers manuals (which
are OK for getting ideas about how things might be done). Some things are not in the factory nor Haynes
nor Clymers manuals. I probably have the details later in THIS ARTICLE.
MOST of you will never have a crankshaft out, let alone be changing one. A few of you may have the
crank out for re-shimming. BMW lower ends are very long-lived, providing they get clean oil
all the time.
A very grabby clutch, vibration, hard shifting, & idle rpm change with clutch lever use (AFTER
full warm-up) usually indicates a need to re-shim the crankshaft. Do NOT get confused here,
as it is normal for idle rpm to speed up SLIGHTLY with clutch lever pull-back, with cold
transmission oil....even in neutral. Details are in this article somewhat further down this page.
Front main bearing and its cap/holder/carrier:
Changing the front main bearing? Confused about its holder/carrier?
Pay attention to the information in the books about properly positioning things; the oil holes being vertical
...and about the drilling needed on the two holes through the bearing...0.124"...right through the existing
front bearing carrier.... and then the bearing area. A new locating pin hole....taper hole, partial at 0.156",
and full at 0.148"....there is a special ream...etc. All this is being mentioned for you, & not put in exacting
detail, to be extra cautious in not just willy-nilly changing/doing things. Things are not always as you
may think they are....ask questions on the Airheads LIST!! If you have the BMW Factory Service
Manual, it will show the front bearing carrier drilling setup.
To remove the front holder you need to use a puller, either BMW's, or a steering wheel type for a car.
Use a good hardened bolt with a countersunk depression (use a lathe), in the crank nose, for protection.
YOU MUST HEAT THE AREA QUITE HOT, WITH A LARGE FLAME TORCH.
DETAILS: There is a bushing (main bearing) in the main bearing cap. Heat the cap to sizzle and press
out the bushing. Reheat to install new bushing. Be sure to line up the oil hole and have the joint properly
offset from vertical (the hole). I can supply a photo of this. Once the bushing is installed, you have to drill
two oiling holes, & ream properly. The bearing cap holes are already 3.2 mm. Details as in the factory
manual must be followed. You will be installing a retaining pin, a taper fit; locking it in place with punch
marks. It prevents the bushing from rotating, &cutting off the oil supply.
Do NOT even think about re-grinding crankshafts unless you are prepared to
re-heat-treat (maybe hard plasma coat; nitriding?) the area that was ground,
& to properly radius the sharp corners, etc. You would need a clever machinist.
The crankshaft has cheeks in the way hindering being re-ground. All this
WOULD BE VERY tricky to do. BMW offered its published/available
undersize bearings NOT because a used crankshaft can be reground,
BUT, because of RARE production use of undersized crank journals.
The nitride type hardening of the stock crankshaft is not very deep! Due to
the weights on the crank being in the way, I don't think you will be able to
grind a crankshaft anyplace, let alone re-nitride treat it; or do plasma coating,
ETC. If you find a company that can AND DID do all this for you, please let
me and the Airheads LIST know about it!
Crankshaft end play, spacers, etc...The TECHNICAL DETAILS:
Crankshaft end play is set via two thrust washers at the rear end of the crankshaft. One each of
selected thickness thrust washers (they come color graded for thickness) is used, and it is
common to have them of different thicknesses in the same engine. These are the thrust washers
with the oil groove and 'strange look' that FIT ON THE PINS at the rear of the crankshaft.
One thrust washer is forward of the casting boss, one behind it.
It is NOT a difficult job to set end play....and ALL the details are just below:
Fairly rarely...after huge mileages usually, one sees an Airhead that has two or more of the
following symptoms: Shifts hard, (BUT isn't input shaft play or lack of splines
lubricant or bad clutch); probably has a lurching, grabby clutch action; idle rpm is
unstable & varies a fair amount with clutch pull-in; there is engine vibration.
A grabby clutch can ALSO come about from clutch parts AND from excessive
transmission input shaft end-play.
If you have an airhead with such symptoms, you will want to check the end-float (end play) of
the crankshaft. You are advised to see an expert, or to get the BMW official information, but
here is likely all you need to know. You will have some color(s) of thrust washers on both sides
of the engine housing boss area. It is these that set the end-float of the crankshaft. SOME
BMW Manuals have the sizes of these WRONG (in converting the mm to inches).
If your existing crank has only excessive end play, you may want to just change the thickness
of the OUTSIDE (rearward) spacer. BMW has specifications on end play, or end-float as they
call it. You need to understand that it varies if oily or dry; BMW does not tell you
about that. The end-float specification is 0.08 to 0.15 mm (which is 0.003" to 0.0059").
This is for DRY. If oily, the minimum is 0.15mm (0.006"). If you have removed the
crankshaft; are installing it.... you may want to lower your labor by installing the thinner RED
spacer inside. Thusly you likely will not have to remove the crank again, just select the
appropriate rearward spacer.
Note that BMW has a limit for wear; it is 0.20 mm (0.0079").
Here are the real values of the thrust spacers:
RED: 2.483 mm to 2.530 mm (0.0978" to 0.0996").
BLUE: 2.530 mm to 2.578 mm (0.0996" to 0.1015").
GREEN: 2.578 mm to 2.626 mm (0.1015" to 0.1034").
YELLOW: 2.626 mm to 2.673 mm (0.1034" to 0.1052").
Crankshaft REAR bearing (a bushing type):
The case is heated to sizzle in the area; the bush pressed out. The case is reheated to
install the new bush. The bushes are available in oversizes to match your existing crankshaft,
if it came undersized. YOU CAN NOT likely have your crank ground properly if the bearing
area is bad. MAYBE. There is a oil groove & oil HOLE in the new bushing. As you look from
the rear of the case, with the pan surface facing you, the joint of the bushing is at the top right,
and the oil hole is at the top. That is, the bush joint is 26° to the right of vertical.
Regarding rod bearings, caps and bolts:
I do NOT reuse the rod bolts!.....
The conrod bolt is a special type, although it looks like a Torx. You can get the tool from
NAPA as part 2305, which is the same as K-D tools part 2305. Be sure to oil these parts
rather well as you assemble them & also put the tab into the cap slot; & the rod on correctly....
that is, the located pins will be facing forward! Tighten the rod bolts slowly, don't use too much
torque at first, so you can check for smooth operation of the rod on the journal....BEFORE
you tighten to the final value of 35-38 footpounds; NOTE that the R80GS, R80R, R100GS,
and R100R are to have the rod bolts tightened in stages, by degrees. Initial preload on
them is 15 footpounds, then you go to 40-45 degrees more.
Additional hints/notes....regarding vibration, noises, etc.:
(1) There have been instances, in the seventies, & suspicions by me of even in the
eighties in some R80 engines, possibly others, that some noisy engines, or engines
with vibrations that have not shown up as being due to anything else... are caused
by out-of-tolerance crankshaft bearing fitment. I do not mean the thrust spacers at the
rear of the crankshaft that set end-play of the crankshaft; I mean the bearing shells &
This is a complicated subject, & reference to a very technical SI is needed. The main
journals should have a clearance, measured by PlastiGauge or other means, of 0.0014"
to 0.0026". If the clearance is over 0.0026", BMW offers a mid-oversize bearing shell,
number 11-11-1-265-437. This is the green one. There are quite a few other such
shells, of various dimensions, you would need the SI, & a fiche or on-line listing(s), &
(2) To measure the front main bearing cap internal diameter, the crankshaft must be
removed, but the cap bolted in place!
Timing chest seals:
There is sometimes confusion over the alternator & camshaft seals used in the the inner cover.
All models use 11-14-1-255-011 alternator seals, probably 28 x 47 x 7 mm...have not measured
to confirm that size.
The camshaft seal up to models built in 9/1975 was 11-14-1-261-193. It must not be use in later
models, or there will be leaks. The later cam seal is 11-14-1-262-977, is 20 x 32 x 7 mm.
See the article on doing a 'timing chain' job on this website.
For the curious, the chain size is 3/8 x 7/32, both SIMPLEX, and DUPLEX.
Crankshaft bearing: For many years, this was number 07-11-9-981-722, and is 35 x 62 x 9 mm.
The bearing number has been changed to 07-11-1-468-882. It is a common bearing, but you
must get the correct GRADE. The bearing is FAG16007-C3
02/04/2008: incorporate all previous revisions; expand and also add information from "being-eliminated"
article engineinternals.htm; clarify details on main seal installation.
02/11/2008: Photos of rear seal installation. Fix typo on which sub-section of article 60. Edit entire
article A/R, for clarity and emphasis.
04/24/2009: Minor changes to text in one photo. Clarify the 90 foot-pounds that are only on the 1981+
05/10/2009: Remove most of the emphasis and base colors, as experiment.
01/15/2010: Clean up article for better clarity, less verboseness.
08/08/2010: Add information on the crank tool from my TOOLS article
08/01/2011: Add Addendum area with note on the REAR thrust washer problem.
06/18/2012: Add minor commentary on the O-ring.
07/29/2012: Flywheel warning sketch replaced by improved clarity version. Clean up article a bit.
09/04/2012: Add "suppose the engine has rotated some...." section. Add QR code; change Google ad
display, add language button
12/12/2012: Insert old crank.htm article and begin to completely revise
05/01/2013: Oil pump O-ring part numbers and description changed.
08/03/2014: improve the description of the crankshaft and bearings tolerances description and why.
04/06/2015: Additional information on the O-ring, and history.
12/24/2015: Update the meta-codes. Revise entire article for layout, left narrower justification, and
reset tables orientation, etc. Clarify some details. Combine sections for clarity.
NO technical details changes.
© Copyright, 2014, R. Fleischer
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