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Resurrected my 850 and it immediately shatters a shim.

  • Thread starter Thread starter isaac
  • Start date Start date
I

isaac

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I have no idea how this happened.

I just got done reassembling the 850 yesterday and after much spraying of gas into the intake got it to fire and rode it around the block and back to my house. Woohoo! It was cool stuff, even if it was only hitting on 2-3 cylinders, the carbs seem to need cleaning, and there is a very noisy valve.

I shut it down (or rather it did that for me) and rolled it back into the garage.

I pulled the valve cover off today, start checking clearances (most are below .051mm - my smallest guage, and two are at .076mm). Then I get my eyes on #3 intake. The shim is missing from the lifter. This is after riding the bike for a mile. I pulled the cam out, and lo and behold the shim is sitting in pieces next to the lifter. The cam nose is a bit chewed on the sides from this.

I used the same set of lifters and shims that were on the bike when it was disassembled by the PO 6 months ago. I have no idea how this could happen. Needless to say, I need a shim and possibly a cam.

Anybody ever have this happen to them before?

Anybody got a shim I could have?

Thanks preemptively for the help.
 
If you lost a shim ? either you went to some ungodly rpm or it was installed incorrectly- too loose. Do you know what size shim you need??
 
I don't know if it was installed correctly. All I really know is it was in the lifter when I installed it, and looked just like all the others.

It measures out to about 2.4 millimeters.
 
The shims are basically only held in by the surface tension of the oil. Of course, the valve clearances in a healthy engine are so small that there's not much chance that the shim will have a chance to pop out as you describe.

However, if the lifter is sticking in the bore or if you revved the engine hard enough to cause valve float, the shim could get spit out. I'd suspect a combination of sticky lifter and loss of oil film under the shim in your case.

I would put in another shim of the same size and re-measure the valve clearance. See if you can spot any buildup or stickiness in the lifter, or maybe a weak valve spring.
 
if that cam shows damage then replace it. you will save yourself alot of grief in the long run. basically a cam is very soft, with a very hard outer layer. if it chips through the hard stuff, it will cause problems.
 
Just be glad you did not pop those valve keepers loose or you would have eaten a valve.

Make sure the valve is not hanging up in the open position. This will increase the gap distance and allow the shim to work it's way out of the bucket. Carbon on the valve stem could conceivably hold up the valve. A broken or weak valve spring will definately cause a problem since the valve will drop. You only need 3/64ths of an inch for that shim to work it's way out.

If there is any damage to the bucket on top of the spring ( that holds the shim) replace it, the slightest nick or damage and it's outta there. The bucket and shim rotates when running, they must be able to do so.

The shims are hardened and that makes them brittle. They can take a serious beating but not when caught betwen something, then they shatter.

You could be seriously injured if anything breaks in there at speed. A great deal of violence takes place at 80 mph in the valve cover.
 
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