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rmz250 / dirtbike valve specs and clearance - help!

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if your valve bucket/shim is bottomed out at 0 ( when at top dead center ) do you shim it a size up or a size down??

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if your valve bucket/shim is bottomed out at 0 ( when at top dead center ) do you shim it a size up or a size down??

so that we understand each other: underneath the bucket is the shim which needs to be replaced if your valves are out of spec. shims need to be replaced as the valves seat surface wears down. the consequence of this wear is that the valve will sit higher as the material gradually wears away thus you need to replace the shimms for a thinner one (down). So if you have zero clearance between the bucket and cam, then you need to replace the shim under the bucket with a THINNER one, which will increase the gap between the bucket and cam to be within tolerance. Typically, specs require a 0.09-0.16mm gap between the bucket and cam for the intake valves and 0.17-0.24mm for the exhaust. take the existing shimm out of your bike and measure its thickness with a caliper. then replace it with a shim that is 0.15mm thinner. Example: if you have measured the existing shim to be 1.65mm and replace it with a 1.50mm shim, the bucket will sit 0.15mm lower on thevalve stem allowing you to be within the proper clearance (1.65-1.5=0.15mm) stated above.

P.S: the smallest valve shim is a 1.20mm, if you need a replacment shimm that is close to this in order to achieve the proper valve clearance, expect to replace the valves in the near future. furthermore, zeroed valves tend to be over constrained, making it dificult to gaurantee a proper clearance by going 0.15mm down on the shim size. so dont be surprised if youve gone down 0.15mm on the shim and only achieve a 0.10mm clearance between the bucket and cam.

Edited by funkinalive

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