Valve clearances settings ?


I know this may have been done to death but I get too many hits searching the archive and I'd be grateful for an answer from you guys.

Am I right in thinking that my valve clearances will only get tighter and not looser ? If so when I set them, is there any reason not to set them at the top end of the tolerance ?

Cheers Shane.


Your clearances will only get tighter over time. However, setting the clearances to the tight, middle, or loose end of the range does have some marginal performance gains/losses in various directions.

I personally always set my valves to the middle to loose end. A loose valve is not bad. A tight valve is bad. My bike is brand new. When I do the first check at about 100-500 miles I will set them to the loose end of the range if any need adjusting.

Another factor is cost. Most shims for bikes cost $5-9 each. You only have 5 total so it's not a big deal but some bikes have 16-20 so it is a

much bigger deal. And of course once you replace a shim it will always be thinner so you will never use the old ones.

My .02.


Shims don't wear. Reusing an old shim is not a problem. A valve *can* loosen as things wear, like cam lobes. The other day, I did the first valve adjustment on a '00 426 and had 3 tight and one loose.


How many miles on the WR you adjusted? I'm interested to know how long owners wait to do the first check. On a new bike I'll probably do it with less than 500 miles.

Yes, you can re-use shims. You can trade them with others. Or, they MAY be used when another valve gets tighter and you can re-use the old shim. I'm in the process of doing a valve adjustment on my old 92 TDM850 (2 cylinders x 5 valves). At 24K I needed to adjust 3 shims. I could re-use one by moving it to another spot and had to get 2 new ones.

I personally have never had a valve that uses shims for adjustment get looser over time. But I'm 99% a street bike guy. Perhaps dirt bike engines wear differently.

The best way, IMHO, to learn how to do a valve adjustment is to find someone relatively local to you who can show you it once. And, it's best to have a 1/4" torque wrench with inch pounds to put things back together with.



It was a YZ and it was almost two years old. The guy knew it was past due for an adjustment.

I've adjusted shim type valves on a lot of different cars and bikes. Cars frequently loosen up over time. It may be the higher rpms road race bikes tend to beat the valve seats down moreso than other mtors run at lower rpms.

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