TORQUE SPECIFICATIONS; USING TORQUE WRENCHES;
CALIBRATION CHECKS;..... PROBLEMS.
For torque values, see:
© Copyright, 2014, R. Fleischer
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 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 10 ftlbs, approximately. 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 a short 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.
I've had, over the years, quite a few private postings to me from 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 many problems were caused by owners not having a proper 'feel' for metals/parts/etc., and not using torque wrenches, SOME problems occurred due to WRONGLY published information by BMW themselves.
It is not always clearly stated if threads are to be lubricated or dry. The Airheads cylinder head 4 nuts at the rocker arm blocks
ARE to have oily threads. Only the later Airheads are specified to have their crankshaft bolts oily (these bolts hold the Clutch carrier to the crankshaft) ....although that is generally OK for the earlier ones. The exact years for the oiled crankshaft bolts are specified later, herein.
It is not always clearly stated if threads are to be lubricated or dry. The Airheads cylinder head 4 nuts at the rocker arm blocks ARE to have oily threads. Only the later Airheads are specified to have their crankshaft bolts oily (these bolts hold the Clutch carrier to the crankshaft) ....although that is generally OK for the earlier ones. The exact years for the oiled crankshaft bolts are specified later, herein.
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 (meaning, actually, Nm, or in whatever metric torque)FIGURES ...IN ALL SERVICE LITERATURE ...INCLUDING RIDERS MANUALS, SHOP MANUALS, etc. BMW meant: do 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!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.
The best and most accurate torque wrenches are generally the DIAL 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 stamped lines, others have little windows which are far easier to read with less chance for mistakes. Do NOT mix up foot-pounds and Nm.
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, is a tubular or dial type that 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 one 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 here. I DO recommend you own an inch-pound torque wrench. A tubular clicker torque wrench (or QUALITY beam type) 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. The 1/2" type is SLIGHTLY better over the long run, as I think the 3/8" type, even with an adapter from 3/8 to 1/2, is sometimes not quite as strong for the FEW really high torque items we sometimes have to tighten. For myself, my standard torque wrench is the tubular type, 3/8" drive; but I also have a cheaper non-dial type non-clicker, beam-type torque wrench that I use for non-critical places and it is 1/2" drive. I also own adaptors to go from 3/8" to 1/2" and vice-versa.
The RANGE of the basic most used torque wrench you should own will likely be "near" zero, perhaps 5 or 7 ftlbs, to perhaps 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, which will likely be RARE. You can extend the 75 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 need a clicker, but can use a common lower cost beam type.
***Caution, as noted above, most clicker torque wrenches become increasingly less accurate and hard to feel or hear the click at low settings. I recommend you test the torque wrench for feel and click, at any low setting you will be using. I recommend not even thinking about using a 100 Nm (or, certainly NOT a 150) max setting wrench for something critical... at, say, under 12 Nm. 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.
Be sure to return the setting on your clicker type wrench to a bit ABOVE zero (or a bit above the lowest scale reading if not zero, most wrenches are like that) 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. DO NOT use a torque wrench to LOOSEN things, that IS considered abusive practice.
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 vice, have the handle horizontal, such that it can be moved up and down. Adjust so when you clamp the square drive the tubular section and handle is near perfectly horizontal or slighty above horizontal.
(2) Hang a known weight from the point-of-pressure at the handle (midpoint of handle), and calculate the foot pounds, from distance and weight. Carefully done, and measuring the distance from the center of the square drive to the string point, this is accurate.
(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.
Distance times weight is how you use the vise method as a double check.
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
That is a good article, and with the sketches, you will get ideas/concepts fast.
NOTE: BMW AIRHEADS 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.
NOTES:#1: There have been instances in which someone has questioned just what BMW meant by its torque figures... often in a specific place, such as the driveshaft bolts on the Airheads. 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 almost always is 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 15ftlbs, 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 to NOT 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 half 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).
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.
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Last check/edit: Wednesday, January 31, 2018