Cold valve lash settings - tighter or looser?

General engine tech -- Drag Racing to Circle Track

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dannobee
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Re: Cold valve lash settings - tighter or looser?

Post by dannobee »

Cam King had the best reply.

But it's not *just* iron vs aluminum. The expansion coefficients of the valves themselves matters, too. Titanium vs the various grades of stainless vs inconel vs steel. And then there's the seat material. Iron vs steel vs beryllium copper/bronze. All have varying expansion coefficients that will alter the valve lash.

If you want to do it right, get it as hot as you normally would (ie, just after racing), then as quick as possible, check the valve lash on a few cylinders. Then let it get stone cold and recheck. The difference between hot and cold lash is specific to that particular engine.

Years ago when nascar lowered our compression rules, we found that Ti exhaust valves were failing and switched to inconel. Our cold lash changed to reflect the differing expansion coefficients of the two valves.

Here's a chart of various thermal expansion coefficients for those interested. FWIW

https://www.americanelements.com/therma ... n-coe.html
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CamKing
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Re: Cold valve lash settings - tighter or looser?

Post by CamKing »

Here's the most important thing to remember.
Every cam lobe profile is designed for a given lash when running(Hot Lash).
There is an opening lash ramp coming off the base circle, and a closing lash ramp going back down to the base circle.
Both of these ramps are a given height from the base circle.
You take the lash ramp height and multiply it by the rocker ratio, and that's the Hot Lash you see on the cam card.
If you run a Hot Lash that is not what the cam lobe profiles are designed for, the cam will not run the way it was designed to run.
Performance and/or Reliability will suffer.
Mike Jones
Jones Cam Designs

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jonescams@bellsouth.net
http://www.jonescams.com
Jones Cam Designs' HotPass Vendors Forum: viewforum.php?f=44
(704)489-2449
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