Baffling Shims - '77 GS750

[Anonymous]

I am having problems achieving the proper valve shim clearance. To spare you all the churning, here's an example to ponder - my 1977 GS750 calls for shim clearance between .03 and .08 mm. When I put in a 2.55, for example, I get less than .03. When I put in a 2.50, I get more than .08. The mathematics on this baffle me...

But here's the question. I can go too tight, or I can go too loose. (Believe me, I've tried every gyration possible to meet the clearance...) Which is best, which is worse? What problems might I run into if the clearances are too small, or too big?

Kevin

[Anonymous]

shims

go for the slightly looser, especically on the exhaust, be sure the #'s side is faceing down

[Joe Nardy]

Definitely go loose. You might get a little noise but you won't burn any valves or lose performance. I've seen the same thing on several 8 valve GS motors. The only thing I can think of is that the shims are worn and are not exactly what the markings say. Have you tried to measure the shims with a micrometer? I didn't try that on the bikes I was working on but I'd be interested to hear the results.

Joe

[SqDancerLynn1]

Their can be some small varation between shims & wear Just make sure the engine is overnight cold before checking

[gspaul]

Rotate the motor a few times, by hand.
To make sure you have got the oil pushed out from under the shim!

[Anonymous]

Thanks for the input, guys. For a little more info - I did use a micrometer to check shim thickness, and have them clearly marked. True, there is some variance on the old ones, but the new ones are pretty much on target for size. The engine is indeed cold--rebuild underway, hasn't been running for a couple of years at least--and I've rotated the crank seven ways to Sunday and a few more.

I'll go with a looser fit and see how it all works out.

Again, many thanks!