When an engine goes from cold to fully warmed up is there less lash(preload) at full operating temperature or when cold?

I realize there is thermal expansion and this changes everything, but could you explain why lash(preload) is more or less hot?

I`ve heard conflicting stories w\ no explanations as to specifics w\ an LT1.

 

Some thoughts:

Metals expand/contract with temperature prestty much depending on the type of metal. Generally steel and cast iron change about 6 millionths of an inch for each inch of length (or width or height) per degree F. Aluminum is about 2 times that much.

So, for example, an 8 inch long steel pushrod heated from 70 F to 210 F would grow about 6/1,000,000 x (210-70) x 8 or about .007 inch.

Everything else, including the iron block, aluminum heads, etc. are all changing temps and changing lengths, so calculating how much valve lash changes would be a daunting task. It is much easier and more accurate to just heat things up to approximate operating temp and measure (and readjust) the lash. Depending on the specific engine parts, lash could increase, decrease or remain the same when checked hot vs. cold.

Setting hydraulic lifter preload hot vs. cold probably doesn't mean a lot, IMO.

I suppose you could set (solid) lash cold, heat the engine to normal operating temp, shut it down and measure the hot lash. This should tell you how much it changed. You should then be able to set a corrected cold lash that would achieve the desired hot lash.

Thought for the day: What happens to the clearance between iron cylinder bores and aluminum pistons as internal engine temperatures rise from 70 F assembly temps?

My $.02

 

Olds do you know if the preload will be more or less on a LT1 once it has warmed up? Aluminum heads, cast iron block, steel rockers, chrome moly pushrods.


And to answer your thought for thr day question I would imagine that the clearance becomes less, on aluminum pistons w\ iron cylinder bores, sine aluminum expands twice as fast.

 

 

Good points OS.

I can tell you that with an iron block, aluminum head engine, the lash HOT versus COLD on a solid is right at .006 ±.001. Nothing scientific to it on my part, just based on my experiences running solids. I will always set the lash hot then recheck lash cold.... record the change and set them cold every time. Don't like working around hot engines.

-Mindgame