Clutch slave size?

[Mr Gazza]

Please could anyone tell me the diameter of a standard clutch slave piston?
I'm after the size of the external type that bolts on the left side alternator cover.

I'm asking for a very good friend who is looking to make his wife's M600 clutch lever a lot lighter to help with her arthritis.
The 600 is an early one with the internal clutch side slave.
So being a very competent engineer, he is looking into boring the cylinder out and making another piston.
He did a series of experimental slaves for my Commando and they all worked well on a test rig, so he knows what he's doing.

If I knew what the standard size for the other side is I could compare that to the aftermarket ones to give him a guide size to aim for. Standard on the internal slaves is 26mm. I've got a feeling the external ones are too?

So far I have 29mm for Oberon and 27-27.5-28.5 and 30.5 for Elovuzione slaves.
If anyone knows what Factory Racing and others are it could be useful.

Thanks in advance.

[Darren69]

There's a chart in this thread:
https://www.ducatiforum.co.uk/thread...iameter.75486/

[Mr Gazza]

Thank you Darren, that's absolutely perfect.

I found it on our very own forum a few minutes earlier and have already sent it to my mate.
It was originally compiled for Avanti Race Parts by Larry Shazaam Kelly apparently.
Name sounds familiar, but...

[stopintime]

Wet clutch on my 800 (maybe on that 600 too?) is the very standard 26 mm. I replaced it with a Yoyodyne 29 mm and that's just about what it can handle. Maybe 30 is ok too. I need the whole range of the lever to go from fully engaged to fully released (no drag).

Just a small real life observation.

[Mr Gazza]

Thanks for the real life observation Lars, those are the most valuable and valid.

I'm also on a 29mm slave with 13mm master.
Interesting that you say your standard slave was 26mm.
The Avanti chart claims they are 25mm.
Unfortunately I no longer have a standard one to measure. Could anyone confirm the standard size of a bolt on left side slave please?

The internal one is definitely 26mm and it makes perfect sense that the two types would be the same to work with common masters.

Has anyone had any experience of boring out the clutch cover slaves?

[stopintime]

Maybe it's easier to solve the challenge at the master? If there are even smaller masters to buy.....

The APTC clutches are quite a lot lighter than the simpler 600/750. I have no idea if the APTC will fit in this 600, but I know that a simple 750 clutch fits in my S2R800 (normally with an APTC clutch), so maybe...

[Mr Gazza]

I think I've now established that the standard slave is 26mm and that the table is wrongly stating 25mm.
Maybe "Shazaam" measured a piston and not the bore, which is what the calculations should be based on.
I knew the name was familiar, he crops up a lot on Ducati forums.

Not so easy to change the master Lars, as it's a fairly stock early bike. (And nice too.)
The standard coffin master for that is 13mm. or more likely actually 12.7mm to be pedantic.
The later Goldline masters are 12mm on the clutch side, but would just not suit the bike.

Besides, my mate is a very accomplished professional engineer and it's probably easier for him to bore his spare cover and make a piston. It will only cost him a a few pence for a seal.

[stopintime]

... and the pleasure of having done it himself.

[Dukedesmo]

Late to the party but, I have an original Ducati clutch slave of the era, albeit from a 916 but I'd be very surprised if Monster, SS etc. used anything different?

Measures 26mm, both bore and piston - OK, piston is marginally smaller but not by 1mm.

[Mr Gazza]

Thanks for confirming that Tim.

Hutch reckons he allows no more than 0.2mm between piston and bore, so we've concluded that Shaazam most likely didn't measure a piston, but where he got 25mm from is not clear. We've assumed a repeated typo!

I'm looking forward to him doing this mod and hope he takes some picture along the way.
When it's all worked out, which it will be, he'll be up for doing these if anyone wants a lighter, or just a non leaking internal clutch slave. Watch this space.

[Mr Gazza]

Things are moving.
The clutch springs have been changed for new standard ones as it was assumed that heavier ones were fitted by a previous owner.
Unfortunately no difference!

He has reported that the seals look a bit swollen possibly and causing too much drag.
Having found that a seal kit is rather pricey and comes with an unwanted piston, we're wondering if anyone knows of a generic alternative to the standard seals or if the kit is available somewhere without the piston?

Any help gratefully received as the seals may well only be tried as an exercise before diving in with the cutters!

Thanks in advance as always..

Note; this is for the early wet clutch 600 engine with internal right side clutch slave.

[Dukedesmo]

Is this the part? https://www.ebay.co.uk/itm/125895925...Bk9SR8aJmoziZA

[Mr Gazza]

It could well be what we're looking for.
Thanks again Tim.