RFS Clutch Slave Cylinder Bore Cracked from Broken Chain

I purchased an '06 525 EXC some time ago, and recently pulled the motor out of the frame to address some other issues. When I removed the clutch slave cylinder, I noticed an issue the previous owner neglected to tell me about during the purchase.

It appears that at some point, the chain broke and damaged the engine case near the clutch slave cylinder (see pics, please). I have noticed that the clutch does not fully disengage (bike lurches a bit going into gear, neutral is hard to find... its worse when engine is cold) ... I did not notice any leaks around this area (mineral oil or engine oil) before or during disassembly. 

The previous owner (or someone) repaired it with some sort of epoxy.

Without doing my due diligence (checking clutch fluid level, bleeding) I hesitate to state that this is the cause of my clutch disengagement issue ... but pardon my ignorance here and help me out: How bad is this?  Am I looking at replacing my engine case here or is the previous owner's jerry rig good enough?






Unless the photo is deceiving, that crack doesn't look too bad to me.  It looks to only be affecting the sealing surface and not the structural support of the main shaft bearing.

Since this is a lot of work to split the cases and then replace the case, I would come up with some sealing method that works and run it until you need to get into the bottom end for some other reason.  Maybe anerobic sealant would be a good choice.  I'm not sure if you can replace just a case half or if they are matched sets.

As far as clutch operation, unless the buildup of all that grey crap was super thick, I can't imagine it caused an issue.

These bike are hard to find to find neutral in unless of course you are going up a steep ass hill and try to downshift to first.

Your lurching issue is likely due to a couple warped clutch steel discs.  Cheap and easy to fix.


Just to confirm what I read - I need only be concerned that this seals? Is this to keep dust out of the cylinder or keep oil in? If it does not seal, what are symptoms?

I'd wager that gray crap is sealant from the previous owner. It does look like some of it got into the cylinder bore. However, its hard for me to tell what should and shouldn't be there.

Thanks for the advice. I will replace the clutch pack while I have the motor out of the bike... fingers crossed!

Probably good idea to scrape all that gray silicon out - clean it up & JB weld it

how does the slave cylinder o-ring & all the seals look ?


Agreed - I will clean up the gasket surface before reassembly and add some JB weld if there are any recesses that need help.

The O-ring isn't really O shaped anymore .... there is an obvious "flat spot" or ridge that goes around the whole thing. 

Now that I'm looking - that gray crap is all over the cylinder, and the slave cylinder itself is damaged. I can see porous metal from where a chip broke off (right side of 2nd photo). Ugh. 




Edited by Brannnt

There are three points of sealing in the slave cylinder.  There is an o-ring on the outside of the piston that's under the snap ring in your photo.  This keeps clutch fluid (mineral oil) inside the slave.  Next there is an o-ring that goes around the outside of the slave cylinder as well as a flat gasket that goes between the slave housing and engine case.  These two keep engine oil inside the engine.

Your slave needs to be replaced as the snap ring groove has been damaged.  This damage was likely caused by someone pulling the clutch while the slave was not installed.  Doing this is a big no no as the clutch can easily generate enough force to blow the snap ring groove apart as in your case.  I always write 'do not pull' on a piece of paper and tape it to my left hand guard when my clutch or slave cylinder is not installed as a reminder to me but also to my kids.

After replacing your clutch I would recommend just putting it together with the o-ring and gasket and see if it leaks.  Obviously clean up all that grey crap first.  I would avoid JB Weld at this point.  If it does leak, I would try a small bead of Loctite 518 or Permatex 51813 anerobic sealant around the o-ring since this is where your case is damaged.

As far as your clutch is concerned, there likely is no need to change the whole thing unless you are loaded with cash.  I would just measure the friction plates for wear and inspect the steel plates for warpage.  I would bet dollars to donuts you simply have a couple warped plates.

Let us know what you find.

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