TORQUE
SPECIFICATIONS AND PROBLEMS
torquespecs&problems.htm
article 71-A
©
I have had, over the years, quite a few private
postings to me from embarrassed Airhead owners who have made some
expensive mistakes due to
excessively tightening things. While most of these problems
occurred due to the owners not having a proper 'feel' for
metals/parts/etc.,...AND/OR...not using torque wrenches, ONE for
sure occurred due to BMW published information.
The majority of every nut, bolt, screw, etc., in our BMW's has a published
tightening specification.
It is not always clearly stated if the threads are to be lubricated or dry. For sure, the cylinder head 4 nuts at the rocker arms ARE to be oily.
DO NOT trust Clymers or Haynes manuals information!
BMW made some serious mistakes in some publications many years ago in converting metric to english values. They admitted this more than once. I have a copy of a BMW Motorcycle Dealer Bulletin dated way back in March 1982, in which BMW SAID NOT TO USE ANY PUBLISHED BMW CONVERSIONS FOUND IN BRACKETS IMMEDIATELY BEHIND THE MILLIMETER (meaning, actually, Nm, or whatever, torque) FIGURES...IN ALL SERVICE LITERATURE...INCLUDING RIDERS MANUALS, SHOP MANUALS, etc.
BMW meant not to trust THEIR published foot-pounds of torque!
I personally know of BMW Nm
to foot-pound conversion mistakes....such as in the Factory
Workshop Manual....for the R60/7; R75/7; R80/7; R100/7; R100S;
R100RS; in section 33. There are others and not just in BMW
literature. Some errors were carried over by Haynes and Clymers books....they
continued with the wrong conversions, never checking them.
In general, the metric specifications (Nm,
which is Newton-Meters) are correct, so long as one knows
about any possible later updates. However, many of you will have
torque wrenches calibrated in foot pounds, or other
calibrations.
To make this very clear, do NOT use BMW's conversions from Nm to foot pounds, convert Nm yourself to ftlbs.
To Convert
To
Multiply By
Nm
ftlbs
0.738
Mkp
ftlbs
7.23
Ncm
inch ounces 1.416
The best and most accurate torque wrenches are generally the DIAL
GAUGE, commercial/industrial quality, beam wrenches, which few of
you will own.
The next best seems to be the tubular round types often called
'clickers'. Some of these have chromed barrels with hard to
read stamped lines, others have little windows and are far easier
to read, with less chance for mistakes. Do NOT mix up ftlbs and
Nm!!!!
I recommend against the cheap old-fashioned beam-bar (non-dial
gauge) type, EXCEPT for use at the 27 mm rear swing arm locking
nuts on the dual swing arm models or things like shock absorber
or engine bolts....and other medium to high torque non-critical places.
There are a few places that a more sensitive torque wrench is
needed, IF...IF! you use a torque wrench, instead of by
feel. The camshaft nose nut (pre-1979), pan bolts, some
others. The proper torque wrench here is a tubular or dial
type that reads in appropriate values of
INCH-pounds. It is NOT necessary to own one of
these pricier wrenches, a good FEEL is OK, with a short, perhaps
4 or 6 inch wrench.
A tubular clicker round type (or DIAL beam type) IS a necessary
part of any owners garage-kept tool kit if he maintains his own
machine. Get a good one, keep it forever. I suggest
you obtain one in a 3/8 drive size, or 1/2 inch drive if that is
what your metric sockets and allen wrenches of the square drive
type are; with a range of zero or near zero, to perhaps 75 ftlbs
(approx. 100 Nm), which will cover the CRITICAL BMW torque
settings for any of our Airheads; except the nut at the end of
the automatic advance units on the older /5/6 models....and the pan bolts....may
have missed some here??
***Caution: Most clicker torque
wrenches become increasingly less accurate and hard to feel the
click at very low settings...and I recommend NOT even thinking
about using a 100 Nm max setting wrench for something critical at,
say, under 10 Nm.
Be sure to return the setting on the wrench to a bit ABOVE zero (or lowest scale reading if no zero) after each
use, or at the end of the day, so the calibration remains stable.
Don't use it as a hammer, don't store it on the woodstove, etc.
It is hardly necessary to use a torque wrench to LOOSEN
things.
You can have the BEAM type wrench calibrated now and then, usually expensively, or simply clamp the square drive working end in a vice, have the handle horizontal, and place a weight on a string hanging from the point-of-pressure at the handle (mid-point of handle), and calculate the foot pounds. Carefully done, this is fairly accurate. This works for the common beam type...but the clickers have the pivot very close to the working head, but are designed for a known actual torque by an INternal mechanism, so that method does not work...without a bit of modification.
Here is a website that explains just about everything you need to know about torque wrenches, and checking calibration, except a discussion of the DIAL beam type...which calibrates just like the common cheap beam type. Recommending reading:
http://home.jtan.com/~joe/KIAT/kiat_3.htm
BMW's are fairly tolerant to over-torquing EXCEPT in a few areas:
the cylinder stud nuts, banjo bolts at thermostat, valve cover
center nut, nut holding the automatic advance on the camshaft tip
on the old models, flywheel and clutch and u-joint and oil pan bolts.....probably some I have forgotten to mention.
NOTE: Cylinder studs have had a variety of torque settings published, some in error. The true story, as in a BMW bulletin, is that the torque for ALL models at these studs is to be 25 +- 2 footpounds, and the target is 25, NOT 27. See various articles under #60 for more information.
NOTE!....I almost never actually use a torque wrench on the drain and fill and inspection holes. This is particularly so on the driveshaft drain; and MOST particularly so on the later drives that have the oil level inspection plug at the rear of the drive....it is very easy to strip the threads, even if using a torque wrench. There is NO need for those to be overly tight. Please use any listed torque values with some common sense. NOTE that the later rear drive type inspection plug torque is not listed on my website, on purpose!
Revisions:
04/22/2003: add .htm title; minor clarifications and
emphasis here and there.
05/30/2004: add note on cylinder studs
06/29/2004: change numbering of article from 71 to 71-A
02/26/2005: non-critical clarifications
07/16/2006: clarify usage
02/03/2008: remove hyperlink to engineinternals.htm
04/21/2008: add Joe's website url for his torque wrench article plus minor
editing of entire article for clarity.
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