TORQUE SPECIFICATIONS; BUYING & USING TORQUE WRENCHES;
CALIBRATION CHECKS;..... PROBLEMS.
© Copyright 2018, R. Fleischer
For torque values, see:
There are only a few places on an BMW Airhead motorcycle that require torque settings over 72 foot-pounds. Common ones that are over 72 foot-pounds are the transmission output flange center nut; the ring nut & input nut on the rear drive, & the exhaust finned nuts. The swing arm locking nuts can be 72 to 75 ftlbs, not critical. The finned exhaust nuts should be done by feel (IMO); and, I do not torque them as tight as the factory says. Cheap beam wrenches are adequate for most of all these higher torque areas. Never use a cheap beam wrench for the cylinder stud nuts or other critical places. Quality beam wrenches and quality tubular clicker wrenches are what should always be used for more critical fasteners. If you do your own work, I suggest you have two different torque wrenches, one could be a maximum 75 ftlbs; the other should be for inch pounds, perhaps a maximum setting of 200 inch pounds. You want accuracy, so I'd not use the 75 maximum wrench at less than about 8 or 10 ftlbs. There are places on your Airhead motorcycle that are only 4 ftlbs, and you'd use the inch-pound wrench for that (48 inchpounds = 4 ftlbs). The 75 maximum footpound wrench can be used with an extension, and gain the increased torque, up to maybe even 150+ ftlbs required in a few areas. It is possible to increase the torque from a tubular clicker type wrench or a beam wrench. Actually, you can also decrease it if you wanted to, but I recommend against that usually awkwards use.
Over the years I have had quite a few private postings to me from usually embarrassed BMW Airhead owners, and those working on other vehicles, who have made some expensive mistakes due to excessively tightening things; rarely from too little tightening. While most problems were caused by owners not having a proper 'feel' for metals/parts/etc., and not using torque wrenches, some reported problems may have come from WRONGLY published information by BMW themselves.
DO NOT trust Clymers or Haynes manuals information! DO NOT trust BMW-published foot-pound values. The Nm values from BMW seem OK, although sometimes too high in MY estimation, and I will note, in my articles, when I feel that is so.
BMW made serious mistakes in some publications many years ago in converting metric to English values for torque. They admitted this more than once. I have a copy of a BMW Motorcycle Dealer Bulletin of March 1982, in which BMW SAID NOT TO USE ANY PUBLISHED BMW CONVERSIONS FOUND IN BRACKETS IMMEDIATELY BEHIND THE MILLIMETER FIGURES(meaning, actually, Nm, or in whatever metric torque) ...IN ALL SERVICE LITERATURE ...INCLUDING RIDERS MANUALS, SHOP MANUALS, etc. BMW meant: do not trust THEIR OWN 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!
To make this very clear, do NOT use BMW's own conversions from Nm to foot pounds, INSTEAD, convert Nm yourself to foot-pounds, and MARK YOUR LITERATURE. I also suggest you use the values in my torque values listing article, the link is below.
It is seldom clearly stated if threads are to be lubricated or clean and dry. The Airheads cylinder head 4 nuts at the rocker arm blocks ARE to have oily threads. Only the later Airheads are actually specified in BMW literature to have the crankshaft bolts oily (those 5 bolts hold the Clutch carrier, early versions called a flywheel, to the crankshaft). I personally oil all of them, all models, all years.
There is an article on this website that has a very considerable number of the proper torque values for everything: https://bmwmotorcycletech.info/torquevalues.htm
Torque values between systems of measurement.
Foot pounds is same as pound-feet; ounce-inches is same as inch-ounces. Some values rounded.
Nm x 0.738 = foot-pounds
Foot-pounds x 1.356 = Nm
Inch-ounces = 141.6 x Nm
Foot-pounds x 192 = inch-ounces
Inch-pound x 1.15 = CmKg
Mkp (or Mkg) x 7.23 = foot-pounds
The best and most accurate torque wrenches are generally the DIAL TYPE commercial-industrial beam wrenches, which a very few of you may own. These are VERY expensive.
The next best, for general work, and what most of you probably own, is the tubular round types often called 'clickers'. Some of these have chromed barrels with hard-to-read stamping, others have little windows which are far easier to read with less chance for mistakes. Do NOT mix up foot-pounds and Nm.
I recommend against the cheapest old-fashioned beam-bar type, EXCEPT for use at the 27 mm rear swing arm locking nuts on the dual swing arm models or things like shock absorber bolts or engine bolts or transmission output flange nut or rear drive input nut, ....and similar medium to very high torque but non-critical places.
There are places where use of a torque wrench should be considered mandatory. BMW Airheads are NOT tolerant to over-torquing cylinder studs nuts, banjo bolts at oil filter cover plate, valve cover center nut and side nuts, nut holding the automatic advance on the camshaft tip on the pre-1979 models, & oil pan bolts. Torque values are somewhat less critical for the rod bolts, and bolts for the flywheel, clutch, & u-joint.....& probably some I have forgotten to mention here.
There are a few places that a more sensitive torque wrench is needed than the typical 75 ftlb maximum type that is commonly in use. The camshaft nose nut (pre-1979), pan bolts, and some few others. The proper torque wrench for these places, if you use one, probably reads in appropriate values of INCH-pounds, but Ncm or other readouts can be used, if you convert or have the values. It is not absolutely necessary to own an inch-pound wrench, a GOOD FEEL is OK, with a short, perhaps 4 or 6 inch wrench. Anyone who tends to be ham-fisted; or, have no 'feel' for things, WILL want a torque wrench. I DO recommend you own an inch-pound torque wrench. This is a purchase I am wishy-washy about. Since it is used so seldom by owners, I think it probably OK to have one of those inexpensive chrome barrel types with the engraving or stamping, just be careful; and do check the torque wrench for accuracy and that you can hear and feel its click.
A tubular clicker torque wrench (or QUALITY beam type), of perhaps 75 foot-pounds maximum reading, is a necessary part of any owners garage-kept tool kit. Get a good one, keep it forever. I suggest you obtain one in a 3/8 or 1/2 drive size depending on what your metric sockets and allen wrenches square drive sizes already are.
For myself, I also have a cheap non-dial type non-clicker, "beam-type with pointer" torque wrench that I use for non-critical places. These are OK to purchase at garage sales, providing the pointer rests at close to zero reading. I also own numerous adaptors to go from 3/8" to 1/2" male to female and female to male. Mine has a scale of 100-0-100 foot-pounds. I sometimes use it with a 6 inch extension to extend its range.
I have an article that is useful for ANY torque wrench, if you need to extend its range, and better understand angular use:
The RANGE of the basic most often used torque wrench you should own will likely be "near" zero, perhaps 5 or 7 ftlbs, to probably 75 ftlbs (approx. 100 Nm), which will cover most of the BMW torque settings you will have need to tighten.
Torque wrenches being used at below ~12% of maximum torque wrench value tend to get increasingly INaccurate, & the click and click-feel point on many begins to be more difficult to determine. I suggest that you get a 75 foot-pound size; you can always borrow a larger size, if ever needed, ....OR .....you can extend the 75 ftlbs models with a homemade adaptor for the rare use of values over 75, if you do not want to purchase or borrow a higher value torque wrench. For the highest torque value places where you want to use your own torque wrench, you do NOT have to have a clicker, but can use a common low cost beam type.
I have found that, carefully used, the 75 foot-pound QUALITY clickers are OK down to about 6 or 8 foot-pounds. This enables you to use them for the 7.5 foot-pound setting for the swing arm pins.
Return the setting on your clicker type wrench to somewhat ABOVE the zero or minimum reading after each use; or, certainly at the end of the workday, so the calibration remains stable. Don't use it as a hammer, don't store it on the woodstove, etc.
The general rule is to NOT use a tubular clicker type torque wrench to LOOSEN things, that IS considered abusive practice, unless it is a two-direction type. SOME torque wrenches are specifically made so they CAN be used in both directions, such as the zero-center beam types, and are, thusly, usable on left hand threaded bolts, which are common on some automotive wheels.
You can have a torque wrench calibrated now and then, for a formal check it can be $$ ...but, sometimes a simple check is free from your local Snap-On dealer. You can do a quickie check:
(1) Clamp the square drive working end in a soft jaw equipped vice, have the handle as close as possible to horizontal, or very slighty above horizontal.(2) Slowly hang a known weight from the point-of-pressure at the handle pressure point (midpoint or pivot point of handle), probably using a rope, and calculate the foot pounds, from distance between handle center to square drive center... and weight.
(3) Another way to do this is to hang the weight from a point exactly 12 inches from the center of the square drive end. Now you have foot-pounds directly, no calculations. For known weights, bar-bell weights are adequate. But, you can use a bucket, and pour sand, or add anything of weight, into the bucket .....but you need to measure the bucket with sand, etc. Some clicker wrenches do not work internally like others, just as a warning here.
Here is a link to an article that explains some things 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. NOTE that the sketches are not correctly showing how to clamp the square drive ...you certainly do NOT want to clamp both sides of the square drive end, as some wrenches will be bound up or damaged. Clamp JUST the square drive itself! http://home.jtan.com/~joe/KIAT/kiat_3.htm With the sketches, you will get ideas/concepts fast.
The article is not good at explaining using an extension straight-out, and, in fact, hardly implies any such usage, simply saying to use the extension at 90 degrees, which can be very awkward. My own article explains both usages, in depth:
BMW AIRHEAD cylinder stud nuts (and the two other nuts, located at 12:00 and 6:00, that fasten head to cylinder) 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, ALL years, at these studs, should be 25 +- 2 footpounds, and the target is 25, NOT 27, and definitely not 29-31, as in the old /5 manual days.
#1: There have been instances in which someone has questioned just what BMW means by its torque figures. Most often the question is about the driveshaft bolts on the Airheads; because to use a torque wrench on them you cannot just use a socket directly to them. These are the four bolts that hold the Universal Joint to the Transmission output flange. This question usually arises because using a torque wrench at the limited clearance area of the driveshaft bolts requires an adaptor, which can add to the working-length of the torque wrench, INcreasing the torque value from that set on the torque wrench ......unless the adaptor is used at 90°. When this question comes up, it thus is almost always in regards to the tightening method for the 4 driveshaft bolts, that hold the U-joint flange to the transmission output flange. The torque figure is the value on the bolt itself, whether or not you use an adaptor from the torque wrench to the bolt, or, the angle of the torque wrench adapter to the torque wrench. This is standard for industry, and applies unless specifically noted to be different. To re-state this: The torque to be applied to the bolt is the torque the factory specified, and you MUST calculate the adjustment factor for the torque wrench, if the adaptor/extension is not used at 90°. In every instance, except at 90°, the torque wrench will need to be set at a value LESS than the value of the actual torque applied to the bolt head.
#2: A clicker type of torque wrench should be returned to a low setting after you finish using it. Otherwise the internal 'springs' will malform, or, otherwise change characteristics, over time. That time CAN BE SHORT. See the instruction book if it is not clear to you. DO NOT try to return to zero, or below zero, if that is not proper for your wrench! Many torque wrenches do not have a zero setting . Some are marked OFF, or MIN, etc. The best thing is to return it to the area of the lowest usable reading or usable point, or a bit above. On a typical clicker, that is ~10% of maximum reading. Particularly bad is to leave it at a high setting. Pay attention to the details, below:
Many, if not most of you, probably have NO idea of typical specifications (for a good torque wrench), nor, what is inside a GOOD QUALITY torque wrench. Since 1981, I have had a 75 ftlbs capacity Sears Craftsman Digitork Micro-Adjusting Torque Wrench. This was a quite decent wrench then, and still is, and remains accurate. Mine is rated, at time of manufacture, at +- 3% above 15 ftlbs, and +- 1/2 ftlb below 15 ftlbs. That is pretty good, and it is still close to that. BTW ...there is a Federal Specification that it met: GGG-W-686. Mine, like most good ones, has two little windows ...so you do NOT have to try to interpret lines on a shiny barrel. One window is in Nm, the other in foot-pounds.
The mechanism: This is one of the places a quality wrench differs from a poor one. There are two sets of ball bearings inside the barrel, and a dual circular-wound spring set. The spring in a quality unit is very special. Friction is low due to the ball bearings ...so the readings are accurate and consistent over time ....and it has been 35+ years now, and this TW was used a LOT by me, in a shop situation. BTW ....I NEVER allowed anyone in my shop to borrow my TW! It also has a fine-toothed mechanism, so small movements in tight quarters are accommodated. The innards are precision-made. A quality TW is a precision instrument ....that has been ruggedized. There are warnings that came with mine (many inexpensive torque wrenches do not give you any really good information like this):
One warning was not to turn the adjustment more than one revolution either below the lowest scale reading, nor above the highest scale reading (I have never turned the adjustment at all below or above). Another warning says to keep it set below 25% of capacity when not in use (I set it well below that). The cautions further state that if you have left the TW at a reading over 50% of capacity for more than a few hours, then set it to the lowest setting, and leave it there for a minimum of FOUR hours, before using the TW again (I have never left it set high for more than an hour or so). Recommended accuracy check should be done in assembly-line work every 10,000 cycles. (I check mine at vastly less usage). These types of specifications and cautions are fairly typical for quality tubular clickers; most clickers don't tell you any of that.
04/22/2003: Add .htm title; minor clarifications & 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.
01/09/2009: Very minor updates.
06/27/2011: Slight revisions for clarity
10/15/2012: Add QR code, add language button, update Google Ad-Sense; Remove language button & scripting in 2013.
10/25/2014: Add note #1.
08/15/2015: Clarify many details, expanding the text; and a bit more on 08/16/2015.
04/13/2016: Update metacodes; layout, colors, fonts, clarify a few things.
07/19/2016: Revise NOTE #2 to be SURE no one can misunderstand that the test is not specific to the driveshaft bolts, by removing the mention, etc. Update meta-codes slightly, & fix minor scripting problem. Later, added NOTE #3 & updated it again July 22, 2016.
12/19/2016: Check metas & scripts. Clean up excessive HTML. Revise notes section. Clarify some areas of the article.
05/12/2018: Overhaul article. Reduce excessive html, colors, fonts. Clarify some details. Add 10pxl margins. Improve layout.
© Copyright 2018, R. Fleischer
Return to Technical Articles LIST PageReturn to HomePage
Last check/edit: Monday, July 22, 2019