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airhead clutch throw-out rod run-out tolerances

K

kmcbmw

Guest
Hi MOA,

a fellow member and I are working on his 1980 R65 which
has a nasty clutch problem where the clutch disengages
at different places and too quickly. We are trying to determine
if the problem is his throw-out rod having a 0.002 inch
runout.

example: You are stopped at a light and try and slowly
easy out the clutch handle to engage the 'friction zone'
and ease out into traffic. Usually it is nothing, nothing
nothing, nothing, --BAM the bike jumps forward (and
often stalls). Then from 1st to 2nd the problem isn't
as bad since you are going. Then other times at a
light it lets off more smoothly (though still too quickly
for taste) and all is well.

The clutch never slips and always engages properly,
problem is limited to releasing. So we adjusted
everything from the handle to the cable to the
arm in the back of the transmission with no relief.

Became suspicious of the throw-out rod.

Last weekend we removed the transmission and
took out the rod for inspection. It does look a
little worn (flattened) at the tip. We also noted
in the Clymer manual that they say to check
for runout with a glass plate and a feeler gauge.
Well, his has about a 2 thousandth of an inch
bulge in the middle. Is this within spec ? We
thought we had found the source of the problem
and ordered a new one through maxbmw -- but
it just arrived and has about the same runout.

Hoping someone can provide first hand experience
on how straight this rod needs to be, and/or
if you think the problem might be something else.

thank you !

-kai
 
This problem is more than likely excessive end play in the gearbox input shaft. This was common on 79-80s, especially in the R65.
 
This problem is more than likely excessive end play in the gearbox input shaft. This was common on 79-80s, especially in the R65.

interesting. Are you talking about the splined input shaft ? I'll have a look
at that.

Someone else suggested that the piston and bearings were a likely culprit.

-kai
 
Yes, the splined input shaft. If you'd rather not disassemble the 'box to check this, you can put a dial gauge on the cover end of the shaft and warm the cover, then push up and down on the shaft. Spec is .05mm or .002") If it's more than that, you've found the problem.
 
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