DRIVESHAFT
BOLTS, THREADS, TOOLS, ETC.
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drvshftboltstoolstorque.htm-47
You will almost certainly will have numerous occasions to remove or check the tightness of the 4 bolts that are a 12 point type that fasten the forward end of the driveshaft to the transmission output flange, if you own your airhead for enough miles or time. This can be for removal of the transmission for an overhaul or a new clutch or crankshaft output seal, or some other reason, including replacing the rubber boot there, and just plain checking those bolts! You do NOT want them to loosen!
Generally, removing the U-joint bolts is NOT needed for a simple transmission input shaft cleaning and re-greasing (aka 'clutch splines'). It is a good idea to schedule a checking of the tightness of those U-joint bolts at regular intervals. For that purpose, never loosen first, just check in the tightening direction. If even slightly loose, remove, clean the threads so they are clean and dry, and use a drop or two of Loctite BLUE #242 and retighten to 29 MAXIMUM footpounds of torque (20-22 is probably acceptable, but 29 is proper on all later Airheads). If you have lock washers, remove them, replace the bolts with the later shorter type (which appear almost the same, but are very slightly shorter). Loctite BLUE on clean, dry threads!!
If you fail to use the shorter bolts after removing the lockwashers, you can damage the area behind the flange.
If the flange was totally loosened and U-joint
separated (as for a new boot), tighten cross-pattern, evenly, in
stages. If the flanges were separated, be sure the surfaces
are clean before reassembly.
The threads on the bolts
and on the flange, should be oil-free [clean and dry]. This is
per BMW, and I agree. BMW says to replace these bolts
(non-washered type) every time they are removed. I
do not. What I DO is to screw them in with fingers,
and if they are smooth, they may or may not have been stretched
especially just under the head, but I assume not, and I reuse
them, with 1 or 2 small drops of BLUE #242 Loctite AFTER
cleaning the male and female threads with a quick evaporating
solvent. Please be advised that the bolt COULD have had some
stretching just beneath the head, and not in the engaging
threads, which would not necessarily be revealed by my screw-in
test, so this is YOUR call here as to using new bolts, or not.
AGAIN: Please decide for yourself whether or not to replace these
bolts each time they are removed or unscrewed. UNscrewing
direction first to then check for tightness is NOT a good idea.
I have NEVER had a reused set
of these bolts break!!!
The earliest bolts with split type
lockwashers were not torqued as tightly as the later non-washered
ones(20-22 footpounds was generally used) (now is 29 ftlbs max.), and they do not stretch, unless
GREATLY overtightened. At that point, you might even break a
bolt. I will NOT
use the early style 'long' U-joint bolts with the original added
split washers....you WILL have serious problems if the washers
crack or break. I use ONLY
the later, slightly shorter bolts,
withOUT lockwashers. I use blue Loctite on already cleaned
and dried threads, even though I know that the setting of 29
ftlbs (max. at bolt) is increased SLIGHTLY by the Loctite
lubrication (NOT much actually). It is acceptable to
tighten those bolts by hand without a torque wrench, if you know
what that should feel like. You do not have to use 29
footpounds, somewhat less is probably OK. If your threads
are marginal you may want to use 20 or 22. If you do
not use a torque wrench with an adaptor, and a known applied
torque value, you can probably get away with using the tool kit
wrench, which is a 12 point box wrench style, and use "a
good grunt" on the bolts.
The early versions of this bolt were officially 14.5 mm in length, part
26-11-1-230-414, to accommodate lock washer 07-11-9-930-840. The actual
measurement is a faint amount less, that is, 14.4 mm.
The forces at this flange (which is a TAPER fit
to the transmission output shaft, and is why bump
starting is a poor idea) and bolts are very
high;....and, in 1983, BMW eliminated the lockwasher, as
some had broken, and then a bolt would really loosen up....and
soon all 4 were loose. THAT problem went all the way back
to the /2 days! When the flange and U-joint parted
company, the rear of the transmission could be torn off!
This happened to one of my own R60 bikes; which is how I
purchased it so cheaply!
In 1983 BMW began using the 13 mm bolt 26-11-1-242-297, this very
slightly shorter bolt MUST be used
if the lock washer is NOT used, to avoid seal damage. This
updated bolt is the one that is torqued to 40 Nm max (29 ftlbs
max), although some early literature calls for some of those
early bolts with washers to be at this torque level....and BMW
says that at 29 ft lbs, the bolt stretches.
I do NOT believe that. Some manuals and
literature have the torque at 27.5-31 for the 1977-80 models, and
29.0 for the 1981 models. Note that these were before the 29
specified by BMW in 1983. Yes, it is confusing. I
use 29 ftlbs as the maximum, and have NOT seen any bolts stretch
from that. It is entirely possible to
reuse the original longer bolts if they are slightly shortened,
but I don't.
NOTE that BMW's specification is for that 40 Nm, without the "max" I have added. I have never had a problem using 29 footpounds, clean and dry and then Loctited' bolt threads. If you are worried about using that much torque, then use 20 or 22; or a good grunt.
The old original longer bolts, with the split lockwashers had a tightening specification of 17-19 ftlbs, and that was likely adequate, especially if Loctite blue is used on clean and dry threads; still, I will no longer use these longer bolts and lockwashers.
Do NOT use RED Loctite,
it requires a LOT of heat to loosen and remove a bolt installed
with RED Loctite.
I have been informed several times that BMW has either gone back
to the washer design, or at least some dealers are selling the
original bolts and lockwashers, and ERRONEOUSLY
telling customers that BMW went back to the earlier longer bolts
with lockwashers. This is NOT TRUE,
and is due to a mixup with BMW.
Only the shorter, non-washered
bolts are the ones to use. NOTE that the new shorter bolts
need to be inspected VERY closely to see that they are shorter!
TOOLS: My 10 mm 12 point BMW tool 88-88-6-002-560 was
manufactured by Hans Schubert in Germany, for BMW, and there may
have been other makers at various times. Mine was sold with
marking as "00-2-560" for a part number. I have a
feeling that this tool is still available, but the price in my
1995 BMW book was $54.58 retail and $32.75 dealer cost. That is
pretty pricey, even back then. It is true that
one can use a double ended BOX wrench, and then an allen adapter to
your square drive on the torque wrench. I have seen
combo box wrenches with 10 mm on one end and 8, 9, 11, 12 mm on
the other. The original BMW 12 point box end
wrench which some use for this purpose is OK. You must
either use the wrench with a goodly grunt; or, use it with a
torque wrench, and calculate the reduced torque wrench
setting.
The actual BMW tool mentioned above that I own, is simply a square
female drive with a slot.
The actual tool is simple, and PICTURES and more information is
in the TOOLS
article on this site. To describe this tool......a 10 mm 12
point box end wrench has had about 1/3 of its unused end cut off,
and the remaining wrench shaft is forced into a slot in a 3/8
square drive socket adapter, and brazed there. Very crude
looking! I would think that any old socket could be heat
softened, a slot hack-sawed and filed, and a cut-off 10 mm 12
point wrench brazed into position. Thus, this
wrench, of whatever design, has a female square drive and a 10 mm
12 point box end wrench extending from it. You could also
do this even more simply, by not having to cut the slot, but
braze or weld the wrench shaft onto one end of the
socket. Lots of ways to make this wrench.
It is a GOOD idea to have the 10 mm
end be of the offset angle
type. You want that end to fit on the bolt at the
driveshaft, without interfering with the universal joint.
You might, before brazing or welding, check the length of the
torque wrench handle pivot point to the center of its square
drive, and make the adaptor tool welded position something
relatively easy to compute. This is not of any real importance,
as you can always package your little tool with a note, something
like: 'for true 29 ftlbs, set torque wrench to xxx'.
If you have a reasonably good feel you can
probably tighten these 4 bolts without any torque wrench, using
Loctite BLUE. That's why I say 'a good
grunt'. The proper bolts are very tough metal.
Please DO NOT use your 'adaptor' at anything except almost
perfectly straight out (that means parallel...IN LINE WITH THE
TUBE OF THE TORQUE WRENCH) to the clicker torque wrench.
That way, no angle is involved to mess up the calculations.
That makes calculations easy, and no leverage problems or
interferences. Do the calculations and reduce
the torque wrench setting
appropriately, to compensate for the extension. STORE that
clicker wrench with its setting close to zero (standard advice).
revisions:
04/04/2003: revise strictly for clarity
05/10/2003: add some items previously in hints.htm section
of website, and revise entire article.
01/14/2004: Clarifications about the -560 wrench, use of
the torque wrench, and hyperlink to the tools.htm article.
02/15/2005: a few more clarifications
01/30/2008: Clarify that 29 footpounds is the maximum, and
that 20-22 is likely OK with Loctite blue; minor other changes
(grammar)
03/08/2008: Add exact measured bolts information, in bold and color; do
some minor clarifying
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