Issue with gearbox or clutch seems to be slipping

[nicholas]

Hi all, I am not an expert with motorcycles so although it is a bad thing affecting my bike, it is a good opportunity for me to resolve a mechanical issue with my BMW R80.

I think it is the gearbox, but I am not sure if what I am seeing is slipping or something else.... again I'm new to getting my hands dirty.

Some history:
Had the engine and gearbox rebuilt about 4,200 miles ago (this June) I fitted a Harley clutch purch to the bike so have been messing about with adjusting the clutch...it kept creeping out of adjustment where I could not get the input shaft to engage the gears...it would stick in a gear and I found it difficult to find neutral.... just recently I spent a whole day getting the slack sorted out and the clutch has seemed fine.... not sure if this has caused some damage that is appearing now.

This past weekend I had a great ride with the boys (approx 220 miles) but I rode the bike hard and took it to a ton a few times so not sure if it is a lash back

The issue:
Just started last night, when I ride the bike in 1st and 2nd (I think all the gears) the bike accelerates but you can hear the engine revving but it is not going as fast as it should, seems like it is slipping?

Its like a lag (I think slipping?), the bike moves things pickup a bit but then it backs off and lags some again, it is not popping out of gear, just not its usual torque take off etc... Maybe my clutch is not fully engaging with the gearbox?

The bike moves, but the takeoff does not match the sound/revs of the engine if that makes any sense.

Is that classic slipping, is that a gearbox issue? I think if it were an ignition issue the bike wouldn't rev...just feels like something is slipping.

Anyone had this before?

[nicholas]

I just let the clutch out a bit and the slipping reduced...it still did it when I was at about 25/30 miles so I let it out more and it appears better...but I now have a sticky clutch, not engaging easily etc... So this is a new issue I have found, in the past I've had trouble getting the clutch right, I followed the 201-203mm gap between the lever on the gearbox and engine casing, but found that I needed to bring it in a bit more. I have do doubt that I was running it incorrectly for a while... so I am assuming something is cooked.

The trouble is I am running a Harley Davidson clutch purch and the adjustment is done via the cable...so it has been a bit tricky for me to get right. It is only in these last few weeks that I have had time to re-do all the adjustments according to the recommended slack in the lever and distance on arm...

Anyway... wondering if anyone can help diagnose my symptoms, thinking I might need to take out the gearbox and take a look.

[daz]

Sometimes shifting can be difficult if the input shaft spline needs lubed. Has yours been serviced?

[Kurt in S.A.]

There is a specific dimension used if you have the stock setup...since you don't you have to figure things out for your setup. The basic rule of thumb is that when the hand lever is about halfway out, the arm at the back of the transmission should be parallel to the back of the transmission case.

Kurt in S.A.

[bbelk]

What you are getting is most definitely clutch related rather than gear box. I don't have a large number of experiences, but I bought a low millage, 1979 R65 awhile back that had a very funky clutch. It was very grabby. After about a year, climbing a hill in third gear, the engine broke away in an unmistakable way. The slippage was very easy to reproduce.

I changed everything in the clutch, plates springs, and disk, thinking the labor to get there was too much for experimenting. It turns out the labor is really no big deal, and I am sure I spent too much money on parts. Everything in there was within specs except for the diaphragm spring. The old one was noticeably flatter than the new one.

The bike is a joy to ride with its smooth clutch. If I had to do that again, I would disassemble, inspect, and then order parts.

Back to the job itself. It was slow, but straight forward. No big surprises or complications. The scariest part for me is the drive shaft bolts, but its not that bad. The most frustrating part is resetting the boot over the drive shaft. Also, straight forward, but its a knuckle buster.

[nicholas]

Thanks for the tips. Yeah the engine and gearbox have been rebuilt, not by me so I am not sure how much was done. I am just about to rebuild another BMW engine and gearbox tomorrow for another bike of mine so I'll be able to appreciate how they work.

On this bike I did readjust the lock pin on the gearbox to create slack on the lever and then get the distance of the arm to be roughly 201 to 203mm and about 2mm of play on the control... it is just that the clutch didn't work very well, so I needed to bring it in some...however this is now causing it to slip at high RPM.... I'm pretty sure I've done the right thing here so wondering if my use of it incorrectly set has damaged something...

I am not 100% sure if the clutch plate and springs were replaced so I'll ask my friend tomorrow as we are doing the engine and gearbox together.

Thanks again for your thoughts.

[nicholas]

OK, my cause is the Harley Davidson clutch perch... it doesn't pull the cable a far enough which explains why it was difficult to select gears when the adjustments were according to the Haynes manual spec... I could only get smooth gear changes when the arm on the gearbox was closer to the crank case...so I think I may have worn my clutch plates now as my bike continues to slip even when things are backed right off... morel of the story, don't put Harley Davidson parts on a BMW. I measured the travel on a normal BMW perch and it was about an inch and my HD one is about 1/3...so it was not engaged enough...so my adjustments must have been riding the now worn clutch plate! oh well, this is how one learns!