how to.....slipper clutch

[Dj]

Ive been told by the shop that im going to get a new clutch through, that the early model zxr750's, dont have slipper clutches, and if they did, it would only be the "R" models that did.

I was under the impression, i could be wrong (and probably am lol) but doesnt installing thinner steel plates , in effect, somehow or other, bring into operation, the slipper clutch?...or something along these lines?

I know its not a must have for the street, but Im keen to explore the idea....

Any input from someone in the know, would be greatly appreciated

Thanks in advance,

Dj

[Strika]

Thinner plates will only make the surfaces of the clutch plates bind with less force causing once again clutch slip, but not as you intended.

There are aftermarket Slipper clutches available that I am sure will suit your ZXR. Have a hunt or ask the shop, they should know. Not sure on cost, but it can't be that dear as a lot of slub level racers have them. HTH

[Tack]

I got this from a web site:

Slipper Clutch A little known fact about ZXRs and ZX7Rs is that all models from 1989 to 2003 are equipped with Slipper Clutches. The reason most people don't know is that Kawasaki set them with minimal slip at the factory. Here are the Racekit tips that allow you to activate them: Tuning the Slipper Clutch. http://homepage.ntlworld.com/webzxr/zxr750r/

go to tech tips section.

[Strika]

I got this from a web site:

Slipper Clutch A little known fact about ZXRs and ZX7Rs is that all models from 1989 to 2003 are equipped with Slipper Clutches. The reason most people don't know is that Kawasaki set them with minimal slip at the factory. Here are the Racekit tips that allow you to activate them: Tuning the Slipper Clutch. http://homepage.ntlworld.com/webzxr/zxr750r/

go to tech tips section.

Wow, alla these years and I never knew! Mint. Top tip thanks Tack!

[Strika]

Below is an excerpt from that site. Now that he mentions it. They called it a back torque limiting clutch back then, but it was never set up like the slipper clutches of today.


If you want to delve deeper in how the Slipper Clutch works, here's a technical write up from Sigvart.

I was out this morning taking apart my clutch assembly to see how it worked.

The primary spring pressure we're dealing with when it comes to the torque-limiter, is the limiter springs (the two star shaped leaf springs - only one spring on pre '94 bikes). This is the spring pressure that keeps the Sub-Clutch-Hub (SCH from now on) in place when you slow down in-gear for a stop sign, because it's the SCH that will transfer pressure onto the pressure plate and make it release the clutch.

Under normal conditions the SCH is engaged to the Clutch Hub by three damper cams, which locks them tight together when the engine is pulling the back wheel.
At this point the SCH is clearing the pressure plate by ca 2.6mm, and is not affecting normal clutch operation.
This distance, 2.6mm, is what we actually are reducing or increasing, and is a measure on how far the SCH have to extend to get to the pressure plate. And once there, it`ll overcome the six-spring pressure and release the clutch.

Under moderate engine braking where the revs aren't that high, the back wheel will transfer its higher speed to the clutch hub and make it go faster.
When the clutch hub is going faster, each damper cam will work against its ramp and will make the SCH work itself away from the clutch hub, and closer to the pressure plate.
But the limiter springs will stop it before it reaches the pressure plate, because the speed difference between the wheel and the engine isn`t high enough.

Under high load engine brakings; where you storm over the race track straight, pulls the clutch at 12.000 rpms, shuts the throttle, hammer down one gear....and dumps the clutch whithout giving any throttle.... then you`ll activate the torque-limiter, if it`s proper calibrated that is.
Once again the back wheel will transfer its speed trough the gear clusters and into the clutch hub, which will force the SCH away and against the pressure plate.
This time the force is so great that it`ll overcome the pressure from the limiter-springs and the six-springs, and release the clutch!
This will prevent the engine from locking up the back wheel, which would make it skip and slide. It will instead partially de-couple the wheel from the engine, and let it run at it`s own pace.

I don`t think the six-spring pressure has anything to do in the limiter operation.
When the SCH is forced away from the Clutch Hub, it`s limited how far it can go before it`s mechanically stopped by solid materials in the clutch hub.
If we take my numbers from when the engine was new to me, six steel plates by 2.3mm would give me a me play of 0.35mm, which is 0.35mm from totally disabled torque limiter.
So if I installed five 2.3mm plates and one 2.6, then I wouldn't have any limiter effect....Because the pressure plate is spaced SO far from the SCH, by the thick stacks, that it can`t extend enough to even reach the pressure plate.

Using my current numbers I`m calculating that the SCH is reaching the pressure plate, and then some...actually 1.05mm passed the reaching point, which will release the clutch in a moderate way. (A good friend of mine just mailed me today after trying my figures, 5x2.3mm + 2x2.0 with 0.6mm spacers under the six-springs. And he Could feel the difference! In his own words: "Well I did the clutch mod and it did make a difference. Not a free wheeling difference but it doesn't hit as hard now, very very nice. Thanks for the info and help.")

I`m all for trying out the limits of the torque-limiter settings, as I have a high-compression, big-cubed engine on a narrow and twisty track, and I need all the help I can get into corners. So I`m gonna reduce the stacks one by one, and note the difference as I go.

As to why I think it`s important to shim the six-springs:
The service manual states that the service-limit-lenght of the clutch springs should be no less than 2mm shorter of the standard length....
Say you have springs who are just 1mm longer than the service limit, and that`s all fine, until you reduce your stack height (and spring pre-load) by 1.5mm.
Then you are 0.5mm under the service limit of the spring pre-load, and that can`t be good for a stock engine, let alone a tuned one.
That is why, I think, the race manual tells you to use different springs when you reduce the spring-preload, so as to keep up the normal spring load, and normal clutch operation.
Which is why I`m shimming up as I`m reducing down stack height, as I don`t have the kit springs, and my friend (and myself) knows that it works with shims.

As for my stacks and shims. With "not new" friction plates, and 7x2.3mm stacks I had an initial free play of 0.35mm. If I had new plates I probably would have been around 0.25-0.15mm. From there on it`s just to reduce the steel plates to your liking, 0.05-0.75 for road, and 0.8-1.6mm for track.

Broadly speaking you can configure three different degrees of slip in the clutch:
Virtually no slip, with 7 x 2.3mm plates.
Medium slip, 4 x 2.3mm and 3 x 2.0mm
And the full one, 2 x 2.3mm and 5 x 2.0
Me and my friend are close to the medium one. Before I made this change I had problems with my rear wheel skidding and drifting out under heavy braking, but that is all gone now. And another thing that tells me this works, and that it can`t be a product of feel and psychology, I can actually hear the back-torque limiter working....
I can hear the engine being revved by the force of the faster spinning rear wheel, then I can hear drop in rev as the clutch is slipping. And if the mismatch between speed and revs are big enough, then it`ll repeat this operation several times under one braking operation.

You will wear them out a little faster with a more active back-torque limiter, but nothing serious I think:-)
Time will tell.

Sigvart

[Smitty]

I got this from a web site:

Slipper Clutch A little known fact about ZXRs and ZX7Rs is that all models from 1989 to 2003 are equipped with Slipper Clutches. The reason most people don't know is that Kawasaki set them with minimal slip at the factory. Here are the Racekit tips that allow you to activate them: Tuning the Slipper Clutch. http://homepage.ntlworld.com/webzxr/zxr750r/

go to tech tips section.

Brad
good post
its an oldie ...but a goodie for those with 7s

cheers

[Dj]

*prints off that article to take n stick under my mechanics nose~


classic, thats more than i was hoping for....thanks a million everyone....lets see what he's got to say now


*snicker*