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scratched/marred aftermarket valve shim?

eil

eil

Forum Sage
So there I am minding my own business, taking apart my 850's head in order to give it a good go-through and to change the valve stem steals. (They weren't leaking to my knowledge but I had the head off and already had the seals as part of a package deal.) I remove the exhaust cam and am greeted by this:

800px-Scratched_valve_shim_2.jpg


Fascinating.

I replaced six of the eight shims two years ago with aftermarket jobbies from the forum's favorite aftermarket supplier. I didn't ride the bike much this last year--this is only after about a season of mild riding. So this is not a high-mileage shim in the least.

800px-Scratched_valve_shim_1.jpg


This is the only one out of the eight that this happened to. All of the others look perfectly fine. The marred shim doesn't feel rough at all, but it's not quite as smooth as all the others either. The matching cam lobe seems to be perfectly fine, but I'll measure it anyway to be sure.

800px-Valve_shim_out_of_bucket.jpg


I am tempted to flip it over, stick it back in and hope for the best. But if this was a shim from a dodgy lot, then the same thing is likely to happen again on this side as well and I'd rather not run the risk of fscking up the cam shaft (or worse, shattering the shim).

The damage pattern is funny. It doesn't look like a foreign object got in there, how would it have made such a precise central pattern? And affect no other shims? There were some teeny tiny metal bits sitting in the pockets of the head where the oil collects, but I can't be certain how they got there because the top end has been sitting torn down in my garage all winter. (Bad Charles! No biscuit.)

The only rational theory I have at this point is that when I adjusted the valve clearances, I might have rotated the cams without a shim in the bucket which caused the edges of the cam lobe to burr which scratched the hell out of the shim during the first few seconds of running until the lobe deburred itself. I don't remember doing that, but it sounds plausible.

Mostly I'm just curious if anyone has seen this before. Thoughts?
 
I've never seen it before but I'd ditch that shim.
 
Oh and while I'm at it, how the heck does one remove the shim buckets? The service manual shows a guy pulling one out with his bare fingers. That was worth a good hearty laugh but not much else... mine seem to be in there pretty good and are slick with oil to boot. Not sure which tool to use that won't scratch the sides.
 
I'd suspect the case hardening on that and use it as slingshot ammo.
The valve buckets do just pull out - try a rubber valve sucker. If they come out so far and stick, there's nothing mechanical holding them in, so it's just a question of giving them a good pull - pliers on the raised lip will do it. They're not made of fine china, and if you have the finesse of a normal human being, you won't damage them.
 
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I did get the bucket out, it was just the first one I tried that was stuck in there pretty good. Poured some more oil into the pocket, worked it up and down a bit and used pliers to gently wriggle it out. The other seven came out with ease.

After rummaging through my spare shims and consulting my last adjustment numbers, I have a 2.60mm which should work fine as a replacement since the clearance measured 0.03mm. Not having to pay $10+ on a shim and wait another week or two for it to get here == priceless.
 
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