Odd clutch problem -cbr900rr

[Ian Geary]

Evening all, I have an odd clutch situation, and thought I'd sense check it on here before giving the bike to a shop to look at.

(Apologies in advance for length)

Its a 1999 fireblade with some 46k, probably original clutch, that didn't seem to slip before hand and generally rode well.

Two weeks back, was riding home and after some uncharacteristic revving and heavy use of clutch (i normally commute quite gentally) the bike had a mini breakdown.

Basically the biting point was right at the end of the lever and the bike didn't seem to make the progress it should - i think the clutch was not fully releasing.

Had 2 weeks on holiday, so whilst away j ordered
- new clutch cable
- new friction plates, steel plates and springs
- new gasket

And set out changing the clutch this weekend, which I've done before (soak in oil, restack in correct order etc)

The new clutch cable had a shorter outer cable for some reason, so i left on the original. Though fitting the cable was really tight, and I had to max out the locknut adjuster, remove all free play at the lever, and partially rotate the clutch lever arm with mole grips to connect up the cable.

(The manual recommends setting these at halfway)

Did it all up, with back wheel on a stand, it span nicely. No oil leaks, so all good.


This morning, all geared up and bike on the drive, put it in gear, let out the clutch ...and...the bike barely crept forward.

So basically the same problem - releasing the lever in full is not releasing the clutch fully in the engine.


Had a poke around this evening: tried the other clutch cable, but as I feared, it was even shorter and with the lever fully released the bike didn't even move.

With no clutch cable attached, the clutch arm rotates back around a little further, and with the back wheel up on a stand, the clutch seems to grip well in gear.


I assume I put the clutch together properly (ithard to get wrong - the same number of plates went in as came out)

So i am wondering what else could cause the clutch cable to have become too tight? (Including a replacement one)

If anyone else ever experienced this, I would be grateful to hear about it.


Ian

[OutInTheShed]

I don't know the specific model. but generally there should be no great preload on the clutch cable.
The release bearing and all the bits that disengage the clutch should be unloaded until you pull the lever.
Otherwise wear will be rapid somewhere.

I would suggest checking everything end to end., from the lever pivot at the handlebar, through the lever at the other end of the cable, the pushrod through the gearbox or whatever, to make sure everything is moving freely, with no excessive lost motion due to slack pivots etc.

Some bikes have an adjustment where the lever at the gearbox end bears on the pushrod.
Maybe that can be eased to give some slack in the cable?
Some bikes have a spring here which puts a small preload in the cable while keeping the gubbins inside the gearbox unloaded until you pull the handle.

With the cover off, you want to see movement of the handle bar lever translate into movement of the cover plate.
If the cover plate doesn't go back, something is wrong!

It can be lots of things, like corrosion on the pushrod binding it, a dead release bearing, bent pushrod.

[Omegasteve92]

Ian Geary said:

partially rotate the clutch lever arm with mole grips to connect up the cable.

I really feel like this is your issue and its staring you in the face. If you have already had to preload the clutch arm and cable to get it to fit, then something isnt right. It should be completely unloaded in its resting state. Either something is bent or its routed incorrectly somewhere. A clutch is "on" until its "off" through lever action.

[Ian Geary]

Thanks both for your replies.

Yes, i was a bit puzzled as to why I had to manipulate the lever forward in order to fit the cable...with other bikes ivr done, just loosing everything off gave enough slack to remove the cable.


I will open up the case again then and see what's what - though you cant really judge how well the lever is moving the clutch with the case off, given the arm is built into the case itself.

[Ian Geary]

Busy week

Anyway, got round to opening up the clutch again, and having a look. The answer was quite simple really.

Clutch cables don't generally shrink, and from what I can see online, the clutch arm is in the "right" place when attached to the cable- it's just that that place is pulling open the clutch.

It was as if the clutch stack is too thin, and the "rest" position of the clutch actuator was still pulling on the clutch end plate (and opening the clutch).

So I dug out my service manual, which specifies the thickness of clutch plates.

Bottom line: there are 2 thicknesses of clutch friction plate for the SC33 - the one I bought off ebay are 0.3mm too thin compared to the version I need. Multiplied by 9 plates it was leaving my clutch stack 2.7mm to thin, which was enough for the clutch end plate to remain tensioned by the clutch arm, even when released.

Quite annoyed with myself as it now means another wait for parts, but at least there is an explanation that fits the problem.

Ian