Exhaust Pipe Finned Nuts
(spider nuts per BMW)
©
exhaustnuts.htm
article #46
There are two basic styles, both finned. The official BMW wrench was a 18-600. Other
finned wrenches may be used, if they fit the fins OK.
Early nut models had some deep dimples/holes in the flat area closest to the head, and that was for the tool-kit lug wrench (spanner). Later
models do not have those holes. Many versions of the FIN wrenches have
been made and I recommend the type that engages a goodly number of the fins, accurately. In an emergency, you can use some sort of 'strap-wrench'
if you are careful.
It is not necessary to remove the nut, only loosen it maybe 1/4th turn, to remove the pipes. It IS necessary to totally unscrew the nut to
clean the internal rings (one or two depending on model) and coat the threads (I
do the rings too) with anti-seize
compound. But even then you need not remove the nut from the pipe, just
slide it down the pipe some. Regular servicing of
the threads is highly recommended.
I used to think that every 2 years or 20K would be adequate, but some
have been known to seize sooner, so I am recommending every year
nowadays. If you fail to do that, you
likely WILL be sawing and
replacing nuts...or, worse, a very expensive repair job.
These finned nuts do have specifications on tightening, but I know few who have done that besides myself...I was curious as to what
MY fin wrench would feel like at that torque level. I am sure some others' have tried it. For those anal enough to try, for
the models before 1981, the value in SOME literature is 101-130 foot pounds, and from 1981 it is 145-159 foot
pounds in SOME literature. I HEARTILY suggest you do NOT
tighten them that tight!! I have a factory manual where in one place it shows a nominal 160 Nm,
and also says 118 +-15 foot pounds. Some confusion is had in the various literature due to
BMW...and others'... wrongly converting Nm to footpounds, and compounding the error backwards.
The Nm figures are correct! AGAIN:::: I do NOT tighten them as
tight as BMW says...I think it promotes problems. It is NOT necessary to use a hammer when tightening, but a good grunt
IS needed. The internal split ring does a fine job of tightening on the pipe.
I like the parts nice and clean of deposits before I use the anti-seize
compound. That means I actually clean the threads, rings, etc. I use
a fine wire type of wire brush for that purpose.
The best anti-seize I know of is the Pure Nickel Special of the Never-Seez brand. That is good for
2600 degrees. The standard Never-Seez is also excellent, and the better buy. The Permatex brand commonly seen (1600
degrees) is
adequate. What you must NOT...NOT EVER DO is lubricate those
threads with WD40 or any common oil.....do NOT DO THAT! Most oils carbonize!
It is, of course, acceptable to oil lubricate the nut threads with anything if you
are having problems getting one off/unscrewed.......BUT:
The problem comes when removing or unscrewing the nuts, if one is going to have
a problem. Sometimes those nuts have been over-tightened, or have self-tightened up really well. I use
an old piece of 2 x 4 (wood absorbs some shock) on the finned long wrench, I have even used a light weight (7 or 8 pound) sledge hammer
or a brass hammer.
The loosening direction is COUNTER-clockwise, in other words, to the left, just like any standard fastener,
as you face the nut, from in
front of the bike. It is normal for the nut to be very tight, then break loose and after 1/8th turn, loosen up rapidly.
Do NOT go overboard with the sledge or wood piece!!! If the
nut loosens a small amount, maybe 1/8th turn, then seizes, you can try running
the engine a few minutes, getting that port and nut really hot, then try
loosening again, sometimes that works. If it does not, squirt more
penetrating oil onto the threads, as the engine is cooling. Let sit
overnight, retry, cold, and hot. See below for another way of looking at
this.
****IF that finned nut, broken loose perhaps a few degrees, and NOW
using your hand on the wrench so as to get a feel for it, suddenly gets very stiff again, you are warned NOT to go farther at this
point. That happens at roughly 1/4 to 1/2 turn most of the time when
there is a problem...but this does not mean ALWAYS. What
to do: Retighten unless it seizes in that direction too,,,, then ...Obtain some sort of thin penetrating oil such as Liquid Wrench or Lock Ease Liquid at a hardware store and soak the threads from the
head side. Let it sit overnight. Without going overboard on loosening torque,
loosen slightly, and then reapply the next day, and try the wrench back and
forth, waiting another day if no progress.. I have had only a modicum of success by using a heating torch on
the nut, then letting the cooling suck in a lubricant, but it is worth a try. Do NOT
force that nut!!!!.....!!!!! A properly loosening nut will loosen
QUITE adequately in a fraction of a turn, and then be hand-removable (no finned
wrench needed)!...or nearly so. Try it hot too!...how hot? 2 or 3
minutes of engine warming hot!
If the finned nut will not loosen or loosen enough without seizing, you MUST cut the nut off! I 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 can be used. No matter what tool.... For the best safety in trying not to damage the port's threads, hold the hacksaw blade at an angle, that is, tilted towards the shiny exhaust pipe somewhat. This lets you make a cut that will go through the nut and stop the cutting on the very hard steel rings inside. You need only make ONE cut, in the same direction as the fins, that is, one place, front to rear.
Do NOT cut into the PORT threads. When you are nearly to the PORT's own threads, try using a pry bar or very broad angled chisel and hammer to split the nut. Again, do NOT overdo this. DO NOT injure the port threads. This means you have weakened the nut by that slot, and you can now force the nut to break or widen further at that cut slot, and then the nut will be unscrewable by the finned wrench. Nuts are cheap compared to repairing the port threads! If you make a minor cut into the port threads, you can repair them with a thread chaser, or possibly the nut!
Do NOT throw the old nut away...you can possibly modify it to be a thread chaser, even though it is rather soft!
There is actually a die
available,
very pricey too, for the 52 mm port threads. They are available at such as
metric supply companies...like MSC. I don't know anyone,
including me, that owns one.
When installing the nut, whether a new one or old one, the threads
must be clean on the male and female portions, and
THEN AMPLY APPLIED WITH quality anti-seize compound. I use a relatively fine BRASS brush, but a
steel brush will work OK. Also apply anti-seize to the rings. If
you have any other parts of the exhaust system ever apart, clean them and apply anti-seize. I do this to the
pipe junctions too. Antiseize is a lubricant and 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.
Hints:
(1) The exhaust system should be installed with antiseize compound at each and
every joining point.
(2) For some
airheads there is BOTH
a split ring and a solid collar, that fit on the pipe, inside the finned nut. To avoid you having to figure out how to assemble
them: The split ring goes next to the head, with the FLAT END towards
the head. The solid collar flat end faces the nut. This will, upon a quick look, put the two slanted surfaces
towards each
other.
(3) If you used an oil for loosening the nut, etc....be sure to use a good
solvent and wash it all away before using antiseize. Put antiseize on the
pipe end, rings, previously wire brushed threads....
(4) Do not mix up left and right side nuts, they are the same, but may have worn the threads differently.
(5) Various folks repair bad exhaust port threads by various
means.
One such person is Ed Korn, see the URL.HTM
resources article, or the tools.htm
article. I prefer real welding and new threads, but sleeves HAVE worked
OK, even though the heat trapped is a lot, theoretically.
Revisions:
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 minor typos