Boxerworks.com

I am a new owner of a 1979 R65 and it is a wonderful bike. Only 14k original miles so this bike has sat around most it's life (indoor storage, no rust minimal dry rot).

I was up shifting while cruising up a large hill and, *bang* the bike no longer will stay in gear. The bike shifts fine through all gears, but after applying light throttle the clutch slips causing a pretty bad grinding/clicking, without accelerating, until RPMs drop and it reengages.

So, my initial thoughts are obviously clutch related. I can't tear it apart for a few days to look for the problem, but, have any of you experienced this?
Any advice to save me some headache?

First make sure that the clutch cable is adjusted properly. At the back of the transmission, the lever should move maybe 5-6mm before engaging or becoming stiff. Also that arm should be parallel to the back surface of the transmission when you have pulled the hand lever half way. At the hand lever, you should have also 5-6mm of free play.

Kurt

Clutches don't wear out in 14K. I wonder if it's possible the clutch splines have stripped although that would be a rare occurrence.

Thanks for some feedback, unfortunately (fortunately), it broke down on my way to work but close to my house so when I return Tuesday I'll let you know what I find.

First check will be clutch cable, after that I guess I get to remove the transmission for the first time.

From what it feels like I would guess the diaphragm spring is not holding proper tension when enough power is being introduced to the clutch. Anything more than maybe 10-15% power will cause full slippage.

Could be that the input shaft seal has deteriorated and allowed transmission fluid to work forward and soil the clutch disk. If the condition is really bad, you might see some gear oil on the shelf below the transmission. You'll see things once you get the transmission out.

Kurt

It would be nice to think it is only clutch slip but "bang" and "a pretty bad grinding/clicking" doesn't sound like clutch slip and that's what led me to think about the cause being mechanical at some point in the transmission.

I surely hope not, but I mean I believe it's possible that there is transmission failure. However, a few things point me to clutch still.

After the incident on the highway I was able to continue to ride for apx 4 miles to get it home. 1st gear feels absolutely normal until about 5-6k, second grabs fine and slips sooner maybe 4.5-5.5k, 3rd grabs fine and slips even sooner and so on. Each shift felt smooth and engaged and disengaged like butter. But once I rolled on the throttle those RPMs would fly up as the slippage started. Only during those moments of slippage did I hear, hard to describe in message, clack clack clack clack bahaha

Maybe there was a failure of the bolts holding the pressure plate on the flywheel, sometime in the past in believe they were upgraded. Clutch contamination wouldn't involve much noise unless there was a delamination of the friction disk, most clutch problems I have experienced usually involved the pressure plate. In your case it isn't a release issue but a lack of pressure or surface contamination.

Ok, finally got it all apart and here is my update

First, the clutch cable is adjusted and working fine. The splines on the transmission and the clutch are in perfect condition.
No obvious trans/engine oil seepage or leaking, also the clutch friction plate itself looks totally appropriate for mileage.

The 6 bolts holding the clutch plate were what I would call "hand tight at best". I know these don't have a high torque spec but I do not think it was accurate while loosening, also there is for sure no loc tite holding them in place.

Think these bolts could cause the issue I am experiencing?

I have a new clutch spring on the way to compare the old one but it won't be here for another week.

The clutch bolts being loose would definitely cause the clutch to slip, but the slipping you described should have left some obvious signs (blueing or glazing) on the disc and friction surfaces. I'm surprised neither is apparent. Your spring is probably OK, they last almost forever.

I've had one case in the past where the driveshaft flange on the transmission output shaft was slipping on it's taper and it felt pretty much like a slipping clutch under load. While it's apart is a good time to check that the big nut is properly torqued.