Does valve clearance increase or decrease when engine warms up?

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02GF74

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It has to depend on the engine, namely the materials used.
It for an aluminium alloy block and head, like on the VMax, I would say clearance increases as the alloy expands more so the camshaft moves a tiny amount from the valve buckets.

But in a cast iron block and cylinder head, it would decrease as the valve train expands more than the cast iron. My Ford crossflow engine (cast iron head/block OHV) ran quieter when hot.

Disclaimer: I'm not entirely sure.
 

DreamV4

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Thanks! It is a good answer, because aluminum head expansion fights steel valve stem expansion. I just need to find data for steel and aluminum.
steel 10 11 17 14 16 (different types)
aluminum 23

Steel Stainless Ferritic (410)
 

mngforce

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Generally, the reason you have valve lash clearance is because the valves grow in length due to heat. And, you don’t want the follower to drag on the heel of the cam. This is also why the exhaust lash is usually more than the intake.

So, under general practice, the clearances tighten up during use (when the engine is up to temp).
Mike Norman
G-Force Engineering Development
www.mngforce.com
 

Parminio

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Generally, the reason you have valve lash clearance is because the valves grow in length due to heat.

That's it in a nutshell.

That's why you have clearances on everything from bearings to valves to ring end gaps. Engineers have already done the math on the metallurgy to determine expansion and contraction of any given engine and its parts.

When you set their specified clearance it's to assure that under operating temperatures the engine will perform as intended.
 

one2dmax

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Clearance decreases as the valve heats up. The head is a great heat sink and passes most of it's temp through the coolant system (provided it's adequate). The valve ways has a hard hot time in there. The exhaust grows more then the intake of course.
 

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