Weird thunking from a 2000 fireblade

Mark says...

Get the rear wheel in the air and spin the back wheel, look and listen
for tight links in the chain and check the condition of the cush drive
rubbers in the rear wheel. It might also be a chipped tooth on one of
the sprockets.

 

I suggested this as the probable cause when he first asked a few weeks
back.

http://groups.google.co.uk/group/uk.rec.motorcycles/msg/d70146db54e8bbfe
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_______
..'_/_|_\_'. Ace (brucedotrogers a.t rochedotcom)
\`\ | /`/ GSX-R1000K3
`\\ | //' BOTAFOT#3, SbS#2, UKRMMA#13, DFV#8, SKA#2
`\|/`
`

 

I know you did but as I said in the original post that the cush
drive rubbers were more or less brand new and I've had them out
and they were all in the right place, not damaged and none of
them were spongy. I replaced them because the gearchange was
getting very harsh and new rubbers sorted this out completely
and the improved gearchange is still there iykwim. As far as I
can be certain I can't believe that it's the cush rubbers. The
bearings are all new as are the dust seals and the o-ring that
sits between the wheel and the sprocket carrier.

I've checked the condition of the rear sprocket when I had the
back wheel off at the weekend and there's no wear marks on it
at all and no chunks missing.

Could the chain have worn such that when load is increased on it
that the chain somehow suddenly 'gives' or maybe the clutch is
worn so that it gives the same kind of lash?

Thanks,

 

Could be a tight link in the chain.

 

The only other thing I've done recently is change from using castrol
chain wax to using a scottoiler. I fitted this about 3 months ago and
have done about 3000 miles on it since. It's really cleaned the chain
up apart from anything else... could the wear on the chain with the
wax be highlighted (for want of a better word) by the gradual cleaning
action of the scottoiler lube and now that wear has manifested itself
as this lash?

I'm not entirely happy with the chain to be perfectly honest. It looks
ok but when I had the rear sprocket off the bike I found that the
people who fitted the chain/sprockets had partially stripped the thread
on one of the 6 bolts and hadn't told me. I only found out when I put
the sprocket back on after cleaning it and the carrier and while the
others torqued up ok this would only tighten to about half the torque
and then just carry on spinning. I had no problems undoing it and
didn't put excessive force (torque wrench) while refitting it so really
don't believe I have stripped it... although admitedly I can't prove
that
but I do enough work on cars and my bike to be pretty confident of
my abilities. However, if they are prepared to just stick it back on
the
bike and not tell me then it doesn't give me much confidence in the
quality of the chain. I've ordered a new bolt/washer/nut (getting on
for a fiver!) and have marked all the bolts with paint for now to make
sure none slip.

Regards,

 

Furry muff. Must have missed that.

OTOH it seems that your problems started at about this time, so maybe
it's till in some way connected to this.

Could be a tight spot on the chain, certainly, or more likely a
stretched area. Not sure if this matches your symptoms though.

Doubtful. If nothing else, the clutch wouldn't be operating a rear
wheel revs, so the thunking frequency would be much faster.


--
_______
..'_/_|_\_'. Ace (brucedotrogers a.t rochedotcom)
\`\ | /`/ GSX-R1000K3
`\\ | //' BOTAFOT#3, SbS#2, UKRMMA#13, DFV#8, SKA#2
`\|/`
`

 

I completely agree but it just doesn't feel like a cush issue. In
my experience if you have a worn cush then you will always get a
lash when you apply any throttle and when you apply a lot of
throttle then you'll get a big bang... this isn't like that. I'll
apply some light throttle and a short period later (after the bike
has started to drive forward) I'll get a thunk. As the bike has
started to drive forward I have to assume that all of the play
has been taken up by the cush drive and the thunk is something
else.

Does that sound reasonable, I'm starting to doubt myself... you
can't go wrong when something falls off or breaks but this sort
of thing really gets on my tits

That's what I figure too and because of the frequency it has to be
something that works at wheel speed which is the cush, bearings
and the chain... I'm counting on this as I don't want to take my
gearbox apart and have to take the <shudder> train.

Regards,