The New And Improved Unofficial R65 Forum V2
Technical Discussion => BMW Technical Q&A, Primarily R65 => Topic started by: Breezerider on March 11, 2009, 09:46:35 PM
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My 78 R65 clutch wants to surge when the motor is running hot.
I just rebuilt the tranny plus new clutch and pressure plates, got the shims sorted out with the correct truing plate and depth gauge, being very careful all the way, triple checking all the depth gauge readings, shim thickness and my figures, greased the drive shaft spline, and it ran great until I got the motor a bit hotter than normal doing some very slow riding on steep twisty dirt roads & trails on a hot day. I'd let the clutch out normally and it would suddenly grab and the bike would lurch forward. I had to go very gentle on the clutch, keeping the torque transfer and revs as low as possible.
Once back on the highway with the motor cooled off, it was fine. But I'm worried that if I work the bike in hot weather, I'll face the same problem.
As I said, the drive splines are properly greased and when used in normal temperatures, it shifts and clutches nicely. The new clutch fit over the drive splines with very little play but slid freely. Is it possible that engine heat is expanding the drive shaft causing the splines to stick slightly to the clutch plate? If so, will normal wear on the clutch plate splines provide enough play over time?
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Mine does that in the town. Look forward to any useful responses as well.
My clutch is relatively new, but my gearbox is not. 110,000 miles. I notice mine in the town, in heavy traffic - i.e. when things get hot.
Always assumed it was a gearbox issue or the driveshaft spring. Not so sure now.
Never had the inclination to strip it down again....
Steve h
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When you replaced your clutch, did you evenly torque the bolts around the circle in a criss-cross pattern? Did you remove or loosen/tighten the flywheel? I am wondering if your flywheel or pressure plate surface is a little bit uneven - such that the plate surfaces aren't all perfectly parallel to each other. This could make the engagement point seem to be different if you got the clutch plates hot from having to do more clutch slipping in slow speed maneuvers. If the clutch had alot of miles on it or was heavily abused before it might have this issue, though these dry clutches in general do not like alot of the clutch slipping , slow speed training maneuvers that the wet clutch bikes will handle with relative ease.
If I do alot of these sorts of thing it will tend to get a bit "grabby" on me, but the difference isn't huge, but is noticeable.
The 78-80 clutches are significantly different than the 81-on clutch
assemblies. When you replaced your clutch, what parts did you replace?
You really do not want wear to occur on the splines - all they have to do is to slip 1 "tooth" on the spline and you'll find yourself going nowhere in a hurry - been there - done that.. :D
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>>When you replaced your clutch, did you evenly torque the bolts around the circle in a criss-cross pattern?
Yes, I went slow and deliberate on all the steps.
>>Did you remove or loosen/tighten the flywheel?
No, the Flywheel didn't need to come off.
>>I am wondering if your flywheel or pressure plate surface is a little bit uneven - such that the plate surfaces aren't all perfectly parallel to each other.
New pressure plates and clutch. The old ones were galled and the old clutch splines were badly worn.
>>This could make the engagement point seem to be different if you got the clutch plates hot from having to do more clutch slipping in slow speed maneuvers. If the clutch had alot of miles on it or was heavily abused before it might have this issue, though these dry clutches in general do not like alot of the clutch slipping , slow speed training maneuvers that the wet clutch bikes will handle with relative ease.
It's not the slipping that's an issue, it seems to be the amount of torque that the clutch feels. If I let the clutch out slowly and keep the revs low, the problem is not there, but If I need to start out quickly or am starting on an uphill street with the engine hot, it's a problem.
>>The 78-80 clutches are significantly different than the 81-on clutch
assemblies. When you replaced your clutch, what parts did you replace?
Clutch and both pressure plates, brand new from Germany.
>>You really do not want wear to occur on the splines - all they have to do is to slip 1 "tooth" on the spline and you'll find yourself going nowhere in a hurry - been there - done that.. :D[/quote]
The splines on the output shaft were in good shape and the new clutch was a good fit, maybe too good, there was almost no play in the mated splines, tho the clutch slid freely when I checked it prior to reassembly of the gearbox.
Maybe the clutch spring isn't doing it's job or that pie pan sheet tin pressure plate carrier thingy is not flexing enough. Dunno.
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I suppose that you could have a worn lobe on the mainshaft in the transmission, or something worn down in the final drive/ring gear or in the spring-loaded "cush" mechanism in the driveshaft, though none of those things would be affected by how hot the engine was that I can tell.
One thing to check is to see how much "free play" you have in the rear wheel - put the bike on the centerstand, engine off, and transmission in 1st gear. rotate the rear wheel by hand until you feel it bump, or stop when your then trying to push/turn the transmission and engine. Do it in both directions. When you go out and ride and think that the problem is occurring again, get off and repeat the process and see if there is any difference in the amount of wheel travel before it meets up with the resistance in both forward and backward rotations. If you note any difference, the problem is somewhere in the transmission to final drive area and we can rule out the clutch.
If the clutch parts all fit well on the lubed, splined input shaft of the transmission and you got them all lined up properly with your tool when you replaced them that sounds good - sliding back and forth easily is a good thing - but having loose fit to the spline teeth is not.
When you took the actuating lever and pushrod assembly off the back of the transmission for this operation, I assume that you gave it a good examination, cleaning, and relubed it with gear oil? If the amount of slack in the clutch cable is adjusted correctly, I am wondering if the locknut on the bolt that pushes on the end of the pushrod piston might be loose ? This might give the appearance of a clutch engagement that changes from one moment to another?
Just making a wild guess at the moment..
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The final drive and input shafts and gears and shifter mechanism were all in A+ condition when I inspected everything during the rebuild. The bike only has 20k miles on it. I have a feeling this has been a problem starting early in the bike's life. The gearbox had been worked on before and the shims were not correct. It was surging badly when I got it, with a loud clunk sound.
I did the final drive free play test and it's all very tight and within specs.
All the clutch activating gear is in good shape and lubed. This is why we have a mystery here. New clutch & pressure plates, good shim adjustment, all components in good shape...I have to conclude that there is a design flaw in the tranny. I seem to read a lot about Boxer trannies. I had two BMW mechanics tell me that the clutch tends to characteristically be grabby.
I'm concluding that the clutch spring (also new) is not doing its job. I'm thinking that I'll see about kludging in a short coil spring under the leaves of the torsion spring, something that will just fit outside the flywheel center bolt which will hold it in position, maybe a shortened large diesel valve spring.http://www.bmwr65.org/htdocs/yabbfiles/Templates/Forum/default/undecided.gif
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So how do you get the freaking smilies to work?
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So how do you get the freaking smilies to work?
Just click on the one/s you like while you're composing text. My fav [smiley=beerchug.gif]
Monte
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Or, click the "view all smilies" and a little window will launch that contains all of them...