yamaha xj750 (1982) very bad knocking?

M

Marc H

New member
this is a shaft drive bike. I dont require any pointless opinions only genuine info. the knocking ( which is so bad it is unridable, almost like a bucking bronco) seems to be coming from the drive shaft, the bikes only got about 30,000, so it should be good for at least another 30,000-50,000. Is there anything else i should check first? this problem did NOT progress, i was riding along then all of a sudden it happened. the 'knock' jolts the bike as if youd ran over a cow!
 
The knock from the shaft drive is probably due to gear backlash (or play in the gears) being used due to a fault with the motor itself rather than a fault with the shaft drive.
I would check that the engine is running right under load first. Could be plugs, ignition coil leads or components, fuel and carburation etc
 
30k on a motorbike which is 27 yrs old is quite high.Motorcycle
engines can run at very high RPM`s and do wear out quickly.
I believe there was a problem with this particular model a few years
after it was launched concerning the shaft drive not being strong
enough to cope with the power output of the bike consequently causing
failure of the shaft.The knocking could be a broken tooth somewhere
near where the drive shaft joins the rear wheel.You will have to strip it
down and see if any of the teeth are missing from the crown wheel
on the rear wheel or the drive shaft.
 
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