Shattered valve shims

Matt Rain

Matt Rain

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Decided to replace my valve stem seals today. Started by re-checking the valve clearances - I had done them 2 years ago and all the intake shims needed to be replaced with thinner ones. Anyhoo, clearances checked out the same as they did 2 years ago.

So I pull the camshafts and - surprise - 2 of the 4 intake shims (for cylinders 2 & 3) are broken in 3 pieces, almost exactly the same way. All the pieces are still sitting in the bucket, nothing is floating around.

What could have caused that?

Coupla things to note:

1) Clearances on this bike seem to *increase* when the engine is warm.
2) Shims are aftermarket (K&L), not Yamahas. Bought them from Bikebandit.

Cheap shims? Excessive clearance when the engine is hot? Timing issue?

Halp.
 
You can see I2 and I3 here:

0wbH7jv.jpg
 
When in doubt use the original Yamaha parts. I can't speak for K&L but you know the OEMs will not fail for sure.
 
Sheet. Any damage to the cam?
 
TwistedKestrel said:
Sheet. Any damage to the cam?
Click to expand...

Yeah, both I2 & I3 cam lobes have some pitting right on the "tip". All the other cam lobes are perfect, intake and exhaust. Mother****er.

Just found a guy in Quebec who's selling a good pair of cams for 20 bucks plus 10 bucks shipping. Let's do it.
 
I was in at Z1 couple weeks back to ask Zaid if I can get shims from him if needed vs getting myself a 'kit'. He asked what kit I was looking at (was one of the aftermarket ones I was looking at) and commented 'I wouldn't use those kits as the shims shatter, just figure out what you need and let me know'

I ended up not needing any shims since they were all in speck but it sounded like it was not uncommon for the aftermarket shims to shatter like you found

Jeff
 
I do my own valve shim clearances when req'd. Always have used oem from the dealer - used to swap them out one for one from the dealer (they used to do it free). In recent years they have been asking for a trade plus $5 each. Hmm didn't like that much but I coughed up the money, this got me thinking about buying a "shim kit". The info about shattered aftermarket shims is an eye opener for me. Thanks all for sharing the info.
 
Do NOT use a/m shims. Always stick with OEM or else... see post #1.
 
Didn't know this. Was using hot cams on my dirtbikes.
Good to know, will shift back to OEM.
 
Rob said:
Obviously it's not clear to everyone. Just trying to help.

Your comment is of great value...to nobody.
Click to expand...


lmao sorry if i hurt your feelings, but all the previous posts were clear - your post was redundant. but it is nice that you were trying to help
 
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I have had Hot Cams shims in my zx10r for 15,000 km without issue, but these are the 7.48 mm shims that are under the bucket and fully trapped and supported by the bucket. The ones in the engine in question here look like shim over bucket where the shim is also the wear surface against the cam lobe and is also only in line contact with the cam. Very different stress situation. The shim over bucket is a lot more stressful on the shim.
 
Also, OEM shims aren't an option if the camshafts have a smaller base circle than stock... it needs thicker than the thickest OEM shims
 
Brian P said:
Also, OEM shims aren't an option if the camshafts have a smaller base circle than stock... it needs thicker than the thickest OEM shims
Click to expand...

could you elaborate on when / why a bikes camshaft would have a cam with the base circle smaller than stock?

as for aftermarket shim kits, i would imagine some are better quality than others. have any techs noted which brands are failing or not failing?

The shim over bucket design is most often found on the older (80's?) bikes. The shim under bucket design is most often found on newer bikes, and prevents the shims from being spit out at the higher revs typically seen on newer bikes.
 
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... when the camshaft in question isn't stock!

It's common for the base circle to be smaller in order for the bumps on the camshaft to be bigger without either hitting other parts of the head or having the contact point on the cam lobe run too close to the edge of the bucket.
 
Brian P said:
... when the camshaft in question isn't stock!

It's common for the base circle to be smaller in order for the bumps on the camshaft to be bigger without either hitting other parts of the head or having the contact point on the cam lobe run too close to the edge of the bucket.
Click to expand...

thanks, interesting info for me. never gave a thought about clearances for those with big lumpy cams.
 
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