I've read a lot of articles on the internet and called the head companies when I started using aluminum heads. I was finding such a big difference between hot and cold lashI thought my engine was falling apart. One techline, Edelbrock, told me their aluminum heads don't expand. I don't consult the techline Edelbrock very often anymore unless it is to beg them to make some improvements in their heads.
In all my tests on aluminum heads I found they expand and lift the rocker shafts away from the camshaft what I figure about .003" and I end up with .005"-.006" more valve lash. So I just run all aluminum heads about .006" tight when cold. I don't like doing hot lash, because, well, IT'S HOT. So now I try to do checks and changes after the engine cools down or in the mornings. Sometimes you just have to do it when it is hot.
Since I was a kid in the 1950's my Dad always told me to open the cold lash on our heads (iron) .002" when cold. I've found so little difference between hot and cold on iron I use the same hot and cold settings. Then I adjust the cold/hot settings to get the best performance from the camshaft.
I don't really care if I have the valve lash exactly where the cam maker says, as long as I know where it is set. I'm going to move the settings around to suit my engine anyway. I personally never open the lash over .004" more than the suggested hot setting. But I've been know to crank 'er down tighter than .004" under suggested hot.[/QUOTE
IQ, it appears you have verified my understanding, with aluminum heads on an iron block the lash will grow a bit from the cold setting to the hot. Sounds like my .003 - .004 experience was in the ballpark. In the old days with iron heads I did tend toward setting lash to be .003 - .004 tighter than recommended when hot with both my roller cams & flat tappet. New motor will be .003 tighter than recommended when cold, maybe even go a couple thousandths tighter than that when cold.
