Valve Shimming - Look Like My Luck Has Run Out

[Fred W]

Taking this theory a little further, would tighter (still within spec) valve clearences improve your top end?

Canadian FJR

Roadrunner has answered that with some real first hand experience. Can't ask for more than that!

I'd just like to add: only up to a point when the valves no longer close fully, which is when you immediately begin eo lose a lot of power and risk burning valves or bending them on the piston crown on high compression interference engines.

Also, remember that the clearance we are measuring are with all of the parts stone cold. I would imagine that gap narrows considerably as the engine comes up to temp, hence the reason for the much hotter running exhaust valves needing a wider clearance gap.

To really change the valve timing significantly would require a different cam grind. If you look at the sides of the lobes of any cam, the ramps to the peak are intentionally made pretty steep. Which means you won't get many degrees of timing variation with changes in clearance.

 

[MCRIDER007]

Also, remember that the clearance we are measuring are with all of the parts stone cold. I would imagine that gap narrows considerably as the engine comes up to temp, hence the reason for the much hotter running exhaust valves needing a wider clearance gap.

There was a pretty good post on one of the C14 forums a while back and it was explained that when you are mixing a aluminum head with steel valve stems the result is going to be different valve clearances at different combustion temperatures. Aluminum expands at twice the rate of steel but the steel parts may get 3-4 times as hot when running under a heavy load for sustained periods. If you are just cruising at moderate speeds the valve clearances may actually increase, however if you take it to the track or do a high speed run then the valve clearances are going to close. How much? Not that much, if your valves are in spec you probably could run at max load all day long and not use more than half the valve clearance.