The New And Improved Unofficial R65 Forum V2
Technical Discussion => BMW Technical Q&A, Primarily R65 => Topic started by: AlfromNH on March 10, 2014, 06:46:57 AM
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My Clymer manual list "Clutch Housing Cover Bolts" torque spec at 23nm / 17ft/lbs. I bought 6 new bolts and wave washers.
Just by feel, that torque seems excessive for these relatively small bolts, and somewhere in the back of my mind I seem to recall reading that it was considered too high a value. Am I imaging that? Is that the correct torque?
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17ftlbs does seem a lot but 16 - 17ftlbs is the BMW specified figure for the early models including R65 (I checked my BMW workshop manual) and 15 - 16 ft lbs after 81. They have been known to be wrong though and Snowbum does suggest 7.5 ftlbs.
I would check the size against a standard 8.8 bolts torque chart. If they are 8mm bolts the 15 - 16 would be OK, if the bolts are 6 mm then that would be too much and 7.5 is probably correct.
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Yes it is wrong and you will snap them if you use this torque. This erroneous value has also found its way into the Haynes manual as well.
You were right to ask. Bullet dodged.
If only I had managed to dodge it as well, the first time I change my clutch.
>:(
Rev. light
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That torque is too high. 7.5 ft/lbs (w/ blue loctite) is the figure I have seen specified for the 79-80 R65 clutch bolts
Just out of interest did you get that 7.5ftlbs figure from Snowbum's site or is it available somewhere else ? What ever it seems you remembered correctly.
Is it the case that R65's have smaller bolts than type 247 airheads and that is the explanation for the higher figure being most often quoted. No surprise that Clymers and Haynes have it wrong s they will have copied the BMW manual.
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Thanks guys, I'm glad I asked.
So now that I torqued them to 20+, should I be concerned about them being stretched or otherwise stressed, or just leave them be?
I'm afraid it'll eat at me unless I change 'em... unless someone can convince me otherwise. :-/
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Does anyone know the bolt diameter and thread pitch ?
I've got a table for standard torques in the BMW shop manual that I have .
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The bolts are m6x1.0, Bob
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The chart shows an M6 bolt, 8.8 grade, 6.5 foot pounds .
Doesn't indicate the thread pitch on the chart, just bolt diameter for this size .
To me, that sounds a bit low for this application, threading a steel bolt into a steel flywheel .
But what do I know !!! :D
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Thanks for the info, Bob. That's about 8.8nm. Considering I have them at better than 20nm, I'm very lucky not to have done any damage. I think I'll get some new bolts :o
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So now that I torqued them to 20+, should I be concerned about them being stretched or otherwise stressed, or just leave them be? :-/
Well, and you probably aren't going to want to hear this. Given that whatever torque value you have imparted to the bolts, they are equal and didn't break int he process, I would leave them the hell alone now as to do anything else invites their total replacement.
What I would do is have a long hard look at your torque wrench. If it was expensive and looks to have adjustment points, I'd be taking it to a good tool shop to have it correctly adjusted (or do it myself if I could figure out how).
If it was a cheap one, or is non-adjustable it correct placement is in the nearest bin, or sent anonymously to a BMW owner you do not like.
It is reading way under correct spec, an M6 bolt is broken long before it gets to 20ft/lbs, an M8 would be marginal.
In fact if I recall correctly the general engineering recommendation (and I am at work and therefore operating on memory) is around 7.5ft/lbs for an M6 and 11ft/lbs for an M8, assuming both are 1mm thread pitch, general grade bright mild. You could add 50% more for high tensile steel and double for titanium.
Now there is a thought, a long time ago a dumb mate of mine who worked in aerospace thought it would be really cool to replace all the M4 and M6 Cap screws in in his Yamaha engine covers with titanium cap screws purloined from work. Shame he didn't use any thread lubricant and an even bigger shame that was about 2 years before he had to try to remove any of them.
Given that this was an XS750 and at the time replacement engines were neither hard to find or expensive, he gave the old girl a birthday with a later model XS850 engine as that seemed cheaper than paying to have the 4 bolts he broke trying to undo and their remaining 20 or so cousins electrically eroded in an attempt to save his existing engine covers.
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Indeed, the torque figure for the EARLIER model R65 (79-80) clutch assembly bolts has been incorrectly spec'ed in various places as the same value for the 81-later clutch carrier bolts, and this is often the cause of woe and wailing. As pointed out, the earlier clutch assembly used smaller diameter bolts, and the 7 ft-lbs for the M6 bolts and no more than 15 fts-lbs for the M8 bolts should be used... this info sourced from snowbum and Oak, and Ted Porter.
If you cinched your M6 bolts up to 15 ft-lbs (or M8 bolts to 20_ft lbs) and they didn't snap off already, they might not snap for a very long time, but if you do ever go back in there I'd be sure to replace all those bolts with new ones at the proper torque setting.
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Here's a chart I use with the M6 figures highlighted for black and zinc plated bolts. If the black finished bolts are oiled threads I would reduce torque by 15%.
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Tony: I was talking in nm, not ft/lbs. So 20nm = ~15ft/lbs. I'm still fortunate they didn't break tho!
My torque wrench is a fairly new Craftsman. Certainly not aerospace-spec, but I think it's trustworthy. :-/
The engine is back in the frame, but the tranny isn't installed yet, so I'm going to replace the bolts before I go any further.
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Hello !
as far as I know, on post 81 bikes, the bolts are M7 allen. And they are stretched on torquing so need replacement every time they are removed.
I did not dismantle a clutch in a long time so I may be miss-remembering ...
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But he's got a '79
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Tony: I was talking in nm, not ft/lbs. So 20nm = ~15ft/lbs. I'm still fortunate they didn't break tho!
You surely are, hence my feeling that if you were talking ft/lbs that your torque wrench needed adjustment or discarding :-) I was mislead because all the other posts were talking ft/lbs. I am glad that you are not facing buying a new Torque wrench.
I also think, given the trivial amount of money involved, that replacing the bolts is a fine idea.
May I offer a tip on clutch centering - beg borrow or steel a dial gauge and center that clutch plate as near as perfect as you can. Then when you fit the transmission to a clutch you know is perfectly centered, run the mounting bolts straight up to torque in three stages. I suspect that the manuals still have nonsense in them about leaving the mounting bolts slack, starting the engine and then engaging and disengaging the clutch - in my opinion a perfect way to ensure that your clutch and gearbox input shaft act like an epicyclic gear.
Why BMW didn't accept the 10pfennigs increase in manufacturing cost and allow for and fit a spigot bearing is quite beyond me. I suspect it was a Teutonic extension of the middle finger to convention.
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Can't read anymore ... :'( :'(
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I made a clutch centering tool with a 16mm socket and a bolt I turned down. I've already mated the tranny to the engine on the bench. I thought that confirmed that the clutch was centered adequately?
I've never heard of leaving the tranny bolts loose while starting the engine! I haven't gotten to that point in the Clymer manual, but I'll look for that.
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I just bolt the tranny on , tightening the mounting bolts in stages, but don't leave anything slack. With a centering arbor your clutch will be properly aligned. Now there *were* some Kbikes and oilheads that had slightly misaligned gearbox mounting holes, but I've never heard of such a thing on any airhead.
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They are 6mm bolt in the 1979 and 1980 heavy flywheel clutches.
6 ft-lbs and a little blue Locktite and no more. This is secret information only known to us.
BMW didn't think it important to tell us this information. 20 ft-lbs means stretched bolts liable to break. Remove and replace these now defective bolts. Sorry.