Testing Slipper Clutch

magg · Post by **magg** » Sun Mar 20, 2011 7:32 am

Have been contemplating a slipper clutch for my NC30 to improve low speed & low gear running. After some investigation, have to my surprise discovered that the NC30 has a slipper clutch. If so, I seem to have lost mine, no free-wheel of any description on over-run into corners or during breaking when riding, quite the opposite, lots of engine breaking.

Info I have also indicates that when bench testing the clutch assembly, the clutch basket should free wheel in the over-run direction & lock in the drive direction. If the one way clutch action is so clear-cut, then surely the rear wheel should free-wheel in over-run when the bike is on a stand, in gear and the rear wheel is rotated by hand.

Anyone able to describe what a working slipper clutch feels like when riding and wether you can free-wheel the rear wheel by hand on a stand.

Also, have a loud gearbox wine, most noticeable in first gear and less so in second, any suggestions as to the cause. Is there a specific bearing etc. that could be responsible for noises in only first and second gears . All the other gears seem ok.

Post by **royster81** » Sun Mar 20, 2011 8:20 am

Ok they have a slipper clutch but it's called a sprag clutch and although it does other an element of free running it's not going to be as clean cut as if you'd just pulled the clutch in, so you'll still have engine braking but not as bad as it could be. I think it's the same as modern ramp slipper clutches.

As for the gearbox whine, it's been a while since I was on mine last but I think they all whine a bit due to straight cut gears.

Could this but what your hearing ?

Post by **CMSMJ1** » Sun Mar 20, 2011 8:36 am

The sprag clutch allows for half the clutch pack to function as a slipper clutch.

In no way would you make any slipper clutch freewheel the wrong way - they don't work like that.

The NC clutch is spot on - it does work but it is not going to allow you to run it like a 2T with no engine braking.

magg · Post by **magg** » Mon Mar 21, 2011 12:26 am

So you could call it a "semi slipper" clutch that works to stop rear wheel lockup with extreme engine rpm to road speed mismatch. Was hoping for something more one way to give 2 stroke type engine breaking. Would make first gear roundabouts & stop start riding a lot easier.

Another clutch related question, have noticed that there is significant clutch drag when stopped, can make selecting neutral difficult. Also, when on the stand, in gear, clutch pulled in, rotating rear wheel by hand requires considerable effort. Would expect some drag due to oil drag between plates but how much is too much?

Post by **Cru Jones** » Mon Mar 21, 2011 3:20 am

magg wrote:Was hoping for something more one way to give 2 stroke type engine breaking.

You need a full-on slipper for that. I miss the slipper I had in my old 600rr. You could still get the back end to slide around a little, but only when you shifted down 4x w/out letting the clutch out in between shifts. Now, on my RS I can do that all day and get no engine braking. I do however have to watch the RPMs. One high-side due to a seized piston is one more than necessary IMO.

Post by **spanky** » Mon Mar 21, 2011 7:36 pm

Do all VFRs have a Sprag clutch?
My K model nc30 locks up something rotten under heavy braking/downshifts like the Mallory hairpin or Edwina's - back end skips around all over the place. My nc35 doesn't though so does that mean the nc35 has an improved clutch setup or is there something wrong with my nc30?

Post by **CMSMJ1** » Mon Mar 21, 2011 8:02 pm

I reckon they do - my road bike is a K and it does, my race bike is an N and it also does...

magg · Post by **magg** » Mon Mar 21, 2011 8:45 pm

The problem is they are not a true slipper. As others have said, only half the clutch pack can "slip", actually free-wheel, the other half is locked to the gear box input shaft untill the clutch lever is pulled. It appears to be a last resort slipper system, that will slip only at extremes as the overload has to be sufficient to make half the clutch pack slip while full spring pressure is applied. I am considering mods to lock all the clutch pack to the sprag clutch & then it would be a full slipper, actually would free-wheel on over-run.

venom51 · Post by **venom51** » Tue Mar 22, 2011 2:49 am

It's not actually half the clutch pack either. We did come up with a restack that reduces the number of fiber plates in the section of the sprag. It's really smooth running into the corner. Requires an additional steel over the stock set up.

magg · Post by **magg** » Tue Mar 22, 2011 4:37 am

True, believe standard is 6 fibre plates in the sprag section & the remaining 4 fibre plates are in the "normal" section. Also, did you mean more fibre plates in the sprag section & less in the "normal" section. Less plates in the normal section would give easier slip.

My only concurn with some plates in the "normal" section & some in the sprag section, is the stress/wear that the fibre plates in the "normal" section suffer whenever they slip, particularly if restacking the plates increases the opportunity for them to slip. The "normal" plates are still subject to the full clutch diaphragm spring tension when forced to slip.

Is there a problem with all the clutch plates being in the sprag section, would need some re-engineering to achieve I know but not impossible.

Testing Slipper Clutch

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