hey my uncle got aluminum heads for his corvette. \ \. i was wondering why does he have to re-torque them after a couple hundred miles. he has to take everything apart again to do this.... ???

 

Aluminum does not react to heat the same as cast iron does. It is a much better conductor of heat so your new heads will heat up faster than the block, and cool down faster too. Not necessarily a bad thing, but until they are properly seated, this *can* sometimes work some of the bolts loose. They will not be real loose, as in noe of them are gonna fall out or anything, but they do need to be re-torqued. The same goes for aluminum wheels, you always wanna retorque them after a hundred miles or so.

 

Not sure of the exact answer for the Corvette but speaking generally, aluminium heads have a higher coefficient of expansion than cast iron. In other words they will expand and contract more then CI as they heat and cool. This in turn causes some 'seating' on a new gasket to take place. As the heads 'seat' they could cause the head bolts to lose some torque and that is why they need to be re-torqued.
If I am wrong, hopefully someone with more knowledge then me will straighten me out.

 

Correct! Torqued many a small block chevy head...still love the old camaros

John

 

also, there is a specific pattern you have to follow when doing this...very important.

 

As JKE said, this pattern is critical. Generally speaking it is starting from the center bolts (or studs) and working in a crisscross fashion in an equal manner to each end of the head. Do it according to the specs for that specific engine. Also don't do the intiial torquing in one go. Take it in two or three equal steps. Second torquing after the head has 'seated' can be done in one go.

 

[quote author=cumminsho2500 link=board=10;threadid=19443;start=0#msg182497 date=1063122861]
hey my uncle got aluminum heads for his corvette. they are aluminum.[/quote]

Are they aluminum?? :

If so, aluminium heads have a higher coefficient of expansion than cast iron. In other words they will expand and contract more then CI as they heat and cool. This in turn causes some 'seating' on a new gasket to take place. As the heads 'seat' they could cause the head bolts to lose some torque and that is why they need to be re-torqued. ;D

As JKE and Mexstan said, the pattern of tightening is critical. Generally speaking it is starting from the center bolts (or studs) and working in a crisscross fashion in an equal manner to each end of the head. Also don't do the intiial torquing in one go. Take it is two or three equal steps. Second torquing after the head has 'seated' can be done in one go.

 

[quote author=Hoss link=board=10;threadid=19443;start=0#msg182598 date=1063133383]
[quote author=cumminsho2500 link=board=10;threadid=19443;start=0#msg182497 date=1063122861]
hey my uncle got aluminum heads for his corvette. they are aluminum.[/quote]

Are they aluminum?? :

If so, aluminium heads have a higher coefficient of expansion than cast iron. In other words they will expand and contract more then CI as they heat and cool. This in turn causes some 'seating' on a new gasket to take place. As the heads 'seat' they could cause the head bolts to lose some torque and that is why they need to be re-torqued. ;D

As JKE and Mexstan said, the pattern of tightening is critical. Generally speaking it is starting from the center bolts (or studs) and working in a crisscross fashion in an equal manner to each end of the head. Also don't do the intiial torquing in one go. Take it is two or three equal steps. Second torquing after the head has 'seated' can be done in one go.
[/quote]


lol