1990 GSX750F clutch slip following rebuild

[katana88]

Following a total engine rebuild I’ve had clutch slip starting at 4 thousand rpm.  The engine has been rebuilt by a UK specialist – no modifications. I first filled the bike with a motorcycle mineral oil (recommended for running –in) and got clutch slip. I inspected the clutch plates and although within tolerance I decided to renew the plates with a good quality Surflex clutch plate kit including new metal plates. They were well oiled on installation and i've renewed the springs and basket bolts. I adjusted the clutch as per workshop manual etc and renewed oil with a motorcycle 10/40 semi in case the mineral oil was the culprit. I’m still getting clutch slip staring at 4K rpm approx.  I fitted an oil cooler with downward facing oil lines. This means that all the oil drains when the bike turns off – leaving the oil level higher around the clutch plates at rest. I'm scratching my head. Does anyone think that this could be having an effect on the clutch operation?  I would welcome any thoughts.  

[Lachie04]

I would not suspect so, I've done the mineral oil run in change to synth but never had any clutch problems with it.

Don't have any experience with upside down coolers on this motor but by other accounts on here shouldn't be an issue the plates will be oiled at any time anyway.

What oil are you using does it have any additives in it? I only use Penrite oil but that's my preference but would only ever use motorcycle formulated oils.

Are you sure the push rod is fully disengaging and not sticking? 

Don't know that brand of plate, were they replaced before you ran it in? Maybe someone else has experience with them

[Gixer1460]

Mineral oil is not the problem - what was used for decades before semi was widely available? Surflex is not a name familiar to me ie not common - most aftermarket clutches, particularly the fibre plates, are not rated highly compared to OEM. I used Barnett which were ok with a slight power increase but got 'hot & bothered' with turbo power!  There is clearly something happening at 4k that is inducing the slip - probably a torque peak that is overcoming the spring pressure - try adding some washers to the bolts to increase the spring preload?

 Ranting now ! . . . . .  UPSIDE DOWN COOLERS DO NOT DRAIN UNLESS YOU DRAIN THE SUMP ! ! !  It is a physical impossibility - air cannot get in to displace the oil as the ends of the pipes are under the oil level.

[canamant]

4000rpm isn't much to start clutch slip at.  I'd check that the correct number of plates are there.  Then make sure you have the right length springs.  Check that the clutch basket isn't notched as this can stop the plates fully engaging.  If it's a cable clutch make sure that there is a bit of end float on the push rod.try putting an extra steel plate in to pack the clutch out a bit.  Sometimes clutches do slip a bit until they get hot and any deposits burn off.  When I ran the 4 spring clutch in my 750 slabby it always slipped for a few laps in practice until it had cleaned itself up then it was fine for the rest of the meeting. 

 

[wraith]

One thing to try as a experiment is to put a bit more free play in the cable and see if it stops.

Is the cable new? If not ever renew it or five it a good clean out as a old and stiff cable can course all sorts of problems.

Last to look at after the above, is the outer basket, has it got big notches in it where the plates have been rubbing?

[KATANAMANGLER]

The low hanging fruit for curing  clutch slip are usually either that a car oil has been used that has friction inhibitors in it or using non OEM clutch fibre plates. I'm not familiar with the brand you've used but there are very few that can hold a candle to the OEM plates that is why they are expensive. My Katana is knocking out 130 BHP on a standard clutch with OEM plates with zero slip. About 10 years ago I bought a set of EBC ( heavy duty) friction plates and they slipped all over the place.

[wraith]

Never use EBC plates they are sh1 put a new set of EBC friction plates in my Kat (gsx1100f motor) and they did not last 200 miles before I was at the side of the road in first gear, with the clutch leaver out and reving it up to 9000  rom and the back wheel did not move  only thing to do with EBC plates is use them as a paper wait