Shimming Valves

[Toddy34]

So given that the spec range for clearances on both intake and exhaust is 0.04mm and shims come in increments of 0.05mm I have an issue getting my bike within the recommended range. All my valves are just under spec on the tight side. Ideally I'd set them in the middle of the spec range however there is no way to achieve that with the available shims.

Looking at the available info it would seem I'm much better to set them loose even if they are slightly out of spec (say 13mm on the intakes and 18mm on the exhausts) than button it back up with the valves on the tight side. I'm going to race the bike so want to set it up on the conservative side since it'll be getting a beating.

 

[ReidMcT]

Definitely go loose. But also consider that the spec range is 0.05mm if you round your measurements to the nearest .01mm, which is reasonable. You can get it in spec with the available shims.

 

[Toddy34]

Thanks, that's what I thought.

I have to round anyway as the feeler gauge only has .01 increments. The problem I had is that I have the factory shims so for example the inlets pass a .07 gauge but not a .08. the factory shim is a 2.46mm. So I could go for a 2.45 which would theoretically put it just in spec but on the tight side (and who knows how long for) or go for a 2.40 which would be just out of spec on the loose side.

Given that valves general tighten over time goes for the 2.40 made sense but I just wanted to run it by the forum.

 

[ReidMcT]

Gotcha. I think in your situation I would go for the loose out-of-spec. Otherwise, I'd keep feeling a need to check them again much sooner than the schedule says.