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Exhaust Pipe Finned Nuts
("spider nuts" per BMW)

Plus: a little on exhaust system installation & replacements

2014, R. Fleischer
article #46

There are at least three styles of finned spider nuts that have been used on AIRHEADS.  Early models had some deep dimples or holes (not through the metal entirely) in the flat area of these finned nuts closest to the head that was for the tool-kit lug wrench (spanner). Later models do not have those holes.  There are at least two sizes of fins. The official BMW wrench was a 18-600. Other finned wrenches may be used, if they fit the fins PROPERLY. Many versions of fin wrenches have been made. I recommend wrenches that engage a goodly number of the fins, and closely the fins.  In an emergency, you can use some sort of 'strap-wrench', but that needs to be done very carefully, usually with a piece of tin can surrounding the fins first.  It is altogether too easy to break fins using a strap wrench....certainly OK if the nut is not to be reused.

The exhaust nuts tend to seize-up if not UNscrewed fairly regularly (a year ... or two maximum) & the threads cleaned & recoated with an antiseize compound.  I recommend this be done on a scheduled YEARLY basis.   Failure to do this has resulted in a lot of woes!...some of these woes can be $$$.

To remove the exhaust pipe, should you want to do that for some purpose (NOT necessary for JUST the yearly finned nut antiseize coating work)... it is NOT necessary to remove the nut from the pipe, just loosen it.


SERVICING of the finned nuts:

It is necessary to totally unscrew the finned nut to clean the internal rings (one or two rings depending on motorcycle model) & to clean the threads and then coat the threads (I do the rings too) with anti-seize compound.   You need not remove the pipes, nor do you need to remove the nut from the pipe.  You need only to slide it down the pipe some.   If you fail to service the nuts regularly, you likely WILL be sawing & replacing nuts ...or, worse, repairing threads (which can be an expensive repair job).  The nuts are not cheap, but, much better to saw one & replace it rather than ruin the port threads & have to repair the port threads.  I recommend that the exhaust pipe surface, where the spider nuts & rings fit, be cleaned, perhaps with a brass brush, of any deposits.  I have gone so far as to cut down a brass brush, so as to get into the threads better.

This is one of the few places over-gooping is not a problem, just messy.

DO NOT over-tighten the finned nuts!   I believe BMW's torque specification IS TOO HIGH!  The finned nuts do have specifications on tightening. For the models before 1981, the value in SOME literature is 101-130 foot pounds. From 1981 it is 145-159 foot pounds in SOME literature. Some literature says 160 Nm (118 +- 15 ftlbs). I recommend you do NOT tighten them too tight ....LESS than any of the above specifications will work fine!   I simply use a reasonable 'grunt' on my finned wrench tool.  I don't personally know anyone who actually measures the exhaust nut torque.  If you DO decide to measure the applied torque, some confusion can be seen in the various literature due to BMW ...and others WRONGLY converting Nm to foot-pounds, & compounding the error backwards.   The Nm figures are correct but quite high in MY opinion.    It is NOT necessary to use a hammer on the wrench when tightening; just a good tightening but NOT hardly your full weight, assuming a reasonably long wrench (mine is ~ 12"). The internal split ring(s) do a fine job of tightening on the pipe ...especially if you clean the ring(s) gap of deposits.

I like the parts cleaned of deposits & other crud before I use the anti-seize compound.  That means I actually clean the threads, rings, etc.  I use a medium-fine-small wire brush for that purpose. You COULD use an old stiff toothbrush on the threads.   I use an old feeler gauge to clean the ring gaps.  I am OK with you using a steel or brass brush.

One of the best anti-seizes I know of is the "Pure Nickel Special" which is a Never-Seez brand.  Rated to 2600 degrees.  Our exhaust ports do not get even hardly near half, so the carrier holds up well.  The standard Never-Seez nickel is also excellent and likely the better buy. The Permatex brand commonly seen (1600 degrees rated) is adequate.  Copper-containing (but NOT ALL COPPER) antiseize compounds, if the high temperature type, are OK to use.  Many anti-seize compounds contain copper, whether or not they say so on the container, and copper is actually not needed ...but not deleterious, and a small amount in the applied compound MAY be helpful, but I have not appreciated the appearance after years of such as application to such as studs into aluminum.   An infamous profanity-spewing guy who does Internet videos on BMW repairs, insists on "copper" antiseize. I believe he has no idea of the composition of various anti-seize compounds ....silvery-looking or not!  For various reasons, I recommend against high copper percentage anti-seize compounds, and I absolutely recommend against graphite types.

BMW specified Never-Seez, misspelling it Never-Seize:

So, just what are those numbers?   BMW issues Service Bulletins, which are usually entitled Service Information. Note the S, and the I.  Thus, we BMW Wrenches call these bulletins "SI's".  In February of 1989, BMW issued that SI, under dating order 18 005 89, and the SI had a sequence number of 2335.

WHAT YOU MUST NOT DO ... is lubricate those threads with WD40 or any common oil ...DO NOT DO THAT, because most oils carbonize over time and miles at the exhaust port area due to heat, corrosive fumes, etc.  NOTE, however, that my advice does NOT prevent you from using an oil/solvent penetrant for helping to remove a stuck/frozen finned nut ...but all the remaining oil must then be removed, before the threads, etc., are coated with anti-seize compound, & assembled & tightened.  To make this clear:  It is completely appropriate & acceptable to lubricate the nut threads with anything if you are having problems getting one off/unscrewed ...but do thoroughly clean off such before proper cleaning & re-fitting.

What causes the seizing over time & miles is the galling from steel & aluminum contact, plus the slow evaporation & conversion of the binder (carrier) oil of the antiseize compound mixture ....., plus some carbon & corrosive products from combustion byproducts .....& some changes from other smaller effects.

The main thing about any antiseize goop, & there are many types, is that what is important for our Airheads, except for specialty types that are only for a very specific or a few metals, is that the main material is not corrosive or electrically reactive (dissimilar metals type); AND, that the CARRIER is compatible with the type of heat we get at these nuts.  You remove them, & use a mild wire brush (brass brushes my favorite here) on the threads & the one or two rings, then a feeler gauge on the gap, but clean/brush especially to get rid of carbon & other hard things.  Brush on some anti-seize compound, & assemble without overtorquing.  Do it yearly.  The carrier, particularly in some cheaper anti-seize compounds (but that is only a generality) tends to burn-away, or carbon up. For our Airheads, having some copper in the anti-seize formula MIGHT be slightly helpful ....but you may not visually see that color.

The reason the nuts have been such a PIA, is not totally the lack of cleaning re-gooping regularly (probably the biggest cause though), nor is it unheard of for someone with reasonably OK goop on the threads to find the nuts pretty well frozen after an actually reasonable period of time. There are things going on, besides the goop carrier & the goop's other ingredients; and besides dissimilar metal reactions. One is overtorquing.  Another is that the exhaust port & the threads is a place where nasty stuff accumulates. Some of this stuff is sulfur 'stuff' (or other compounds or additives in the gasoline), and they react with moisture, yes I know the moisture is supposed to be instantly driven off my exhaust heat is not ...before very slight damage is done. The compounds, with moisture, create acids.  Acids have fun with the carbon, ETC., from the combustion process. The atmosphere also enters the threaded area from OUTSIDE THE NUT, from the exhaust header side of it. Atmospheric air has moisture, and 'other stuff'.  This especially happens as the engine cools down.  If you do very short trips, the effects MAY be harder on the threads.

There are often small exhaust gas leakages into the exhaust port pipe taper ring(s).  The ring gaps fill & combustion products act like cement. The threads also gather combustion products.  All threaded things MUST have at least a slight gap or they won't tighten from the pressure applied by the nut. BMW specifies a torque, which they have changed several times, but which I think has ALWAYS BEEN rather too high.  Too little & problems increase.  WAY too little & the pipe moves. That is why I do not torque the finned nuts with a torque wrench & adaptor; another reason is that the wear on the nut threads & port threads varies considerably.  I use a good grunt, but not one that hurts my hand, & this is on a 12" finned wrench.  If you are a beefy guy, I am not, be cautious.  There is NO REASON to over-tighten these nuts! Clean the ring gaps with old feeler gauge material; assemble with plenty of antiseize on everything; do NOT overtighten!  I have never seen an instance where REGULAR servicing of the exhaust nuts has not protected against seizure. The operative word is REGULAR.  In SOME instances, it is every 6 months. In most, it is one to two years.  NEVER let it go further!

I like to use anti-seize compound when assembling ANY parts of the muffler system, even the pipe joints.  I tend to install all studs that screw into aluminum, with antiseize compound.   In some situations, I apply anti-seize to other screw/bolt/nuts situations too.   It is particularly important with steel into aluminum, and especially so with steel studs and bolts that do not have such as cadmium plating on them.  One of the worst instances is with stainless steel parts, which are exceedingly rare on BMW's, mostly they are aftermarket items.  SS into SS (bolt into nuts) can be awful, over time, in corrosion areas.


The biggest problem is trying to remove/unscrew the finned nuts.   Sometimes those nuts have been over-tightened, and/or have self-tightened due to the various already described effects.  QUITE OFTEN the problem is simply that the nuts have not been unscrewed in a long time, cleaned, and re-gooped.

Method #1 (or #2):  I try loosening the finned-nut with my special finned wrench (see photo below), and hand pressure.  If the nut does not loosen, you must use another Method.  Some folks just start with Method #2 ...and I am OK with that.

Method #2:  Use an old piece of 2 x 4, or 7 or 8 pound sledge hammer, or large brass hammer, on the wrench. The loosening direction is COUNTER-clockwise AS YOU FACE EITHER NUT FROM THE FRONT, in other words, to the left, counter-clockwise ...just like most standard fasteners. There is seldom a problem in giving the nut wrench quite a whack.  The nut will almost always loosen SOME.   If your nut seizes-up AFTER modest loosening ...then see the instructions below the photo. What is often not understood, is that loosening the finned nut by a suddenly applied sharp force can sometimes work better than just a heavy force on the long wrench from your hand.  It is NOT just the amount of force applied ...but the contact speed and weight of the sudden shock-force application.

Unfortunately, the nut could, after less than maybe a half-turn, tighten-up.   If the nut loosens a small amount, AND then seizes; it is time for method #3:

Method #3: Use a large flame torch on the NUT, getting THE NUT fairly hot all-around, then try tightening/loosening again. Sometimes that works; often it does not, because you are also heating the threaded port threaded area, which expands fairly fast.  You can also just ride the bike a few miles, then immediately try tightening/loosening.   DO NOT ...NOT!!!  put large amounts of force on the nut after the first loosening-up.

If the finned nut does not continue to loosen more easily or not loosen at all, DO use the following oily penetrant method.  Run the engine (maybe 2 minutes of running the engine at a bit above idle, perhaps 1500 rpm), then turn off the engine.  MULTIPLE TIMES squirt a very thin penetrating oil onto the threads as the engine is cooling. Squirt a number of times as it cools. The idea is that MAYBE the cooling-down will 'suck' some penetrant into the threads & into accumulated carbon and other deposits which are mildly porous.

Let the motorcycle sit overnight, squirt the mixture once more, then try loosening & tightening back & forth just a little ...not too much, and not too many times and do NOT force the nut!   If you do not have to ride the bike soon, do cold soaking of penetrant over & over for a week, then try loosening the finned nut.

It is now well known that an especially good penetrating oil mixture (that beats all others at any price) is a mixture of ATF (automatic transmission) oil with added acetone.  One part oil to one or two parts acetone is the standard recommended mixture.  I suggest you slow down the evaporation of the acetone by adding some slower evaporating solvent, such as paint thinner or kerosene (called parafina in some countries) to the already made acetone and ATF mixture.  This will make the mixture stay wet for a longer period of time.  It works better that way.  I mildly soak a strip of cotton cloth with the mixture, and wrap it around the wet threads.  I use a piece of solid copper wire, without insulation, to keep the wet cotton rag in place. Once temperature is down enough, I put a plastic baggy around the whole finned nut assembly, to try to keep the threaded area wet.   I have had good results with acetone, mek, etc. 

IF, after trying the above methods, the finned nut loosens a bit, & then, using your hand on the wrench (with only MODERATE pressure), suddenly gets quite stiff again, you are hereby warned NOT to go farther at this point with trying to loosen the nut.

DO NOT force the nut if it re-seizes!!!

After trying a penetrant, if the finned nut will not loosen without seizing, you MUST cut the nut off!  The slow method is to use a hacksaw blade holder (see hardware store) that holds a short piece of 32 pitch hardened hacksaw blade.   A common electric motor powered (Dremel?) tool with appropriate cutting disc can be used, but be careful!  No matter what tool, to avoid damaging the port's threads, hold the tool somewhat towards the exhaust pipe.  This lets you make a cut that will go through the nut & stop the cutting on the very hard steel rings inside.  If you do not know where these parts are located, inside the nut, find out. I like to cut on a slight angle, and do it very neatly, so as to save the nut for use as a thread chaser.

You need only make one cut, front to rear.  AVOID damaging the threads ..... Do NOT cut into the PORT threads. When you are nearly to the PORT threads, try using a pry bar or very broad angled chisel & hammer, to split the finned nut at the cut area.  DO NOT overdo this. DO NOT injure the port threads!   The purpose of the cut slot is to weaken the nut so you can force the nut to widen ...or break the cut slot, then the nut WILL BE easily un-screwable.  Now is the time to flood the threads again, with your solvent/oil mixture, before unscrewing the finned nut.  Some cut two slots, ~180 degrees apart to weaken the nut more, or to allow the nut to come off in halves,  more on this below.

Nuts are NOT expensive compared to repairing port threads!   If you accidentally make a minor cut into the port threads, you can repair them with a thread chaser, or possibly the old nut!  You could, of course,  spend the money for a real 52 mm die to fix the threads.  YES! ...there is actually a die available, pricey too, for the 52 mm port threads.  They are available at such as metric supply companies such as MSC.

You have choices ...make a second cut at roughly 180, and the nut comes off the pipe in halves ....or, avoid the second cut by removing the header pipe, so the old nut slips off.  In some instances, you might not want to throw the old nut can possibly modify it to be a thread chaser, the metal is hard enough.

When installing the nut, whether a new one or old one, the threads must be cleaned on the male & female portions.  I use a BRASS brush.  Stiff shortened bristle toothbrushes can be used, as can soft/fine steel brushes.  Clean the gap in the ring(s).

AMPLY APPLY anti-seize compound to the threads and to the outside of the rings ....perfectly OK to do that after the nut & rings are on the pipe.

If you have any other parts of the exhaust system ever apart, clean them & apply anti-seize. I do this to the pipe junctions & small screws in the clamps threads, etc.  Anti-seize compound really helps with nuts, screws, the pipes, spark plugs etc., where they get hot ...but, since it is a lubricant, you do not want to over-tighten things.

If you do NOT over-tighten, & if you remove the finned nut, clean the items & apply fresh anti-seize once a year, you will NEVER have a problem, assuming reasonable threads condition in the first place.

(1) The exhaust system should be installed with anti-seize compound at each & every joining point, & on any threads of joining items, such as the small screws used at the exhaust system clamps.

(2) For many Airheads there is BOTH a split ring & a solid collar inside the finned nut. To avoid YOU having to "figure out" how to assemble them, the split ring FLAT END goes next to the head. The solid collar flat end faces the nut. This puts the two slanted surfaces together.  As you can see, this creates a clamping force onto the pipe, as the finned nut is tightened.  This is one of the reasons I like to clean the split ring slot, so that clamping force is applied without excessive finned nut torque.

(3) If you used a penetrant for loosening the nut, etc. sure to use a good solvent & wash it all away before applying the anti-seize compound.

(4) Do not mix up left & right side nuts, they are the same, but may have differing threads wear.  You won't have this problem unless you remove the pipes, as the nut is captive without the pipes being removed.

(5) Various folks repair bad exhaust port threads by various means.  I prefer real welding & new threads, but some types of sleeves HAVE worked OK, even though the heat trapped is a lot, theoretically.

Exhaust system parts replacements:
To remove the exhaust pipe, should you want to do that for some purpose (never necessary for JUST the yearly finned nut anti-seize coating work) is not necessary to remove the nut, only loosen it ~1/2 turn. There are various brands available:  Epco; Keihan; Sito; whatever JC Whitney is selling; etc.  For quiet sound, good fit, stainless steel, etc, I suggest Keihan, from England.  Those of you in the USA can get these from Tom Cutter's Rubber Chicken Racing Garage (BMW specialist), etc. More extensive listings for exhaust system items & for repairing the threads in the head port, are under E, here:

04/10/2003:  Revised for clarity; add .htm title.
06/30/2003:  Final revision; expand information ...additional clarity.
02/23/2005:  Revise slightly for additional clarity.
03/01/2005:  Add Ed Korn.
03/27/2005:  Emphasis and fix minor typos.
01/09/2009:  Updated, mostly clarifications.
10/30/2010:  Clarified a few details, improved on hints.
04/26/2011:  Minor clarifications.
05/27/2011:  Clean up article.
09/27/2012:  Add QR code, add language button, update Google Ad-sense code; clean up article a bit.
2013: remove language button due to problems.
11/07/2014:  Expand the article somewhat, and, again on 05/06/2015.
02/20/2016:  Update metacodes; narrow the article; update the article; clean up; increase font sizes; add photo of my exhaust finned nut wrench.
06/16/2016:  Update metacodes, scripts, minor article improvements.
01/20/2017:  Final check on metacodes, scripts, layout, fonts, colors.  Clarify a few details.

2017, R. Fleischer

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Last check/edit: Thursday, April 06, 2017