It’s my understanding that with aluminum heads you should adjust the valves .005-.006 tighter when the engine is cold than when it is hot because of the way aluminum expands. Looking for confirmation.  

Good Morning
Hope this works.
http://forums.y-blocksforever.com/Topic68227.aspx?Keywords=valve%20lash%20aluminium%20heads 
stuey

For the cold valve lash on aluminum heads, I will tighten the valves an additional 0.005”-0.006” to compensate for the aluminum expanding as they get hot.

Lorena, Texas (South of Waco)

Thanks for confirming that. 

I'm confused. It's been said that the cold lash on iron heads should be .001-,002 looser to allow for expansion. If aluminum heads expand more, shouldn't the cold lash be looser rather than tighter?

I thought the same thing as Black tie. I have a set of aluminum heads and Dove aluminum rockers; what lash should I use.
thanks

It may be similar to an aircraft engine: The heads grow but the block and pushrods don't. 

64F100 57FAIRLANE500

Set the valve lash for iron heads cold at .019" and forget them.  For Mummert aluminum heads cold that lash should be set at .014" and when hot they will have ~.019" depending on your camshaft requirements.  Iron heads grow with the block and pushrods the same so they don't change clearances.  Aluminum expands more than the iron heads when hot.  If you were working with an aluminum block, the clearances would be set even tighter cold.  Joe-JDC.

JDC

It seems to me that the valve-lash (spec) should be ascertained @ engine assembly, whether iron or alum heads before street/track operation.

The lash is set to spec (whether OEM or cam manufacturer) and run at curb idle until the engine warms fully (all of this after proper cam break-in).

You would then check one bank and make any correction(s) (and record any changes over initial adj). At this point, the engine has most likely cooled somewhat so re-start the engine, bring it up to temp and adjust the other bank to proper spec(s). 

Listen for noise and drive the engine (or dyno - $$$) for a period (break-in) and re-check adj. recording any lash change. This should give you an idea of how lash may change with whatever setup you are running.

An alum cyl head will have different a different expansion rate than say an iron head. Same for an alum block/heads.

Another factor with alum cyl head expansion is the push-rods not expanding with the alum heads and becoming shorter (or rocker arms height raising) at temp upsetting proper valve-train geometry. Another consideration is the differing expansion rates of iron and alum and the alum cyl head moving/walking on the iron block.

KULTULZ - CDO (OCD in correct alphabetical order).

____________________________