Slipping drive, not clutch/gbox/shaft or bevelbox

could anyone help with the following please

I have a 1987 K100RS 8v which has just completed 100K miles.

At about 90mph the drive failed, & the max speed I could achieve was about 20mph, even down hill.

I suspected a clutch failure, although I could not build up speed significantly down hill, which suggested it was not this.

Replaced clutch with one from "Spare" bike, no difference in performance, replaced again with new clutch plate, spring plate, no difference.

Replaced drive shaft, splines were worn, no difference, replaced bevel box, no difference, replaced gearbox, no difference.

I can turn the engine over against compression by rotating rear wheel & by rotating the flywheel with gearbox removed.

The engine starts instantly, no noises.

I can only think that the splines on the output shaft to the fly wheel are slipping. I assume if the cush drive was breakign up I would still have drive & a loud metal to metal clonk as drive was taken up.

I have not stripped the top, or is it the side! Of the engine to investigate as I am now losing the will to live.

Any helpful suggestions would be, well really helpful.

Thank you in advance.

maybe!
have a look at those pictures...

you have to use special grease ("Staburags") every 30.000km for monolever!

Hi thanks for the link to the pictures, this appears to be the drive shaft bevel box spline.

My original unit was showing signs of wear, but I have replaced the drive shaft & bevel box with another pair of units. The lack of forward moton was not cured.

Or are these pictures of the shaft running internally to drive the flywheel via the Rubber cushion drive.

REgards Mark

Do you get any drive at all?

If you put the bike in gear when on the centre stand and let the clutch out does the back wheel rotate and rise in speed with rpm? If you now apply the back brake does the engine slow down?

If it's not the output shaft, the clutch, the gear box or the the bevel box, then there's not a lot left ... only the big gear that transfers the crankshaft power to the output shaft, and you'd definitely know if that had gone!!

If the splines on the bevel box / drive shaft had failed, then you would be able to rotate the rear wheel freely even with the bike in gear, but this can't be the case as you say that you can turn the engine over by using the rear wheel?

Is the clutch push rod moving freely?

When he says that he can "turn the engine over against compression with the rear wheel" makes me wonder how good his compression really is.
I'd suggest a compression test personally. If for nothing else but to rule it out.
Loose plugs can give you grief as well.
As one who has lost valves at only 60mph it deffinately cuts the output power.

Hi,

All,

I can do a compression test, but up to the time of the failure the bike would still redline in 5th with an indicated 135mph, so it is still performing as an almost new bike.

The engine runs sweetly, instant start even if left for a couple of weeks, just normal oil burn if left on side stand on start.

With the bike on the centre stand the back wheel revolves & at low rev's applying the brake can stall the engine.

With the bike off the stand, you can pull away but if you apply the front brake you can raise the rev;s with no forward motion.

If this had all happened after I had replaced the clutch I would have assumed I can't fit clutch plates, but the symptom has been the same from , loss of drive, throu fitting 2 different clutch plates 2nd hand & new, 2nd hand bevel box. drive shaft & gearbox. (these items from a bike I have owned for number of years & were workign before I scrapped the bike)

The push rod is the older type with the aliminuim piston & appears free, 2 of these have now been used from original & replacement gearbox. I have tried adjusting this to the minimum posible dis engagement so gears can only just be selected, still only minimal forward motion.

There is mention of the main transfer gears failing, these drive the shaft to the fly wheel, has anyone experienced the splines on this shaft failing?