Aluminium Head Gaskets

[Taliesin]

I'm on half of rebuilding a Husky 4 stroke engine which I have fitted a 100mm piston.The head gasket supplied was aluminium.Any advise on torque setting, should it be more or less than the standard steel issue??
Should the head be retorqued after 1st run of engine?
I figure as Aluminium has a modulus of elasticity 1/3 of steel the torqued figure would be less than the standard 37Nm + 90 Degrees any usefull advise appreciated.

 

[Taliesin]

Come on someone must have come across some.Anybody use any gasket sealer on their headgaskets?
I shall retorque down tommorrow failing that I'll try the standard gasket.

 

[Rich Rohrich]

Is the Husky supplied torque specification based on the aluminum head gasket or a steel head gasket?

 

[Taliesin]

The 37Nm + 90degrees is the standard steel Husky gasket.No torque spec was supplied with the Aluminium gasket.I checked with my supplier who could only say he thought it should be to the the same.It is a bit thicker than standard steel issue.

 

[jmics19067]

this is just a guess but wouldn't the torque settings be the same since you are tightening the same bolts?

I once made a thinner copper head gasket in place of the composite gasket and had no ill effects using the original torque values. Although completely opposite of what your situation is; thinner with less crush.

 

[Rich Rohrich]

If the AL gasket is thicker does it crush down to the same installed thickness as the steel gasket under the same applied torque?

 

[Taliesin]

Well I retorqued down the head this morning ran the bike same problem a slight leak all around the head.Wasted a whole day with this problem.
Decided to go back to a new Genuine gasket.Problem solved!! Thank god!! The ally gasket didn't show any sign of squashing I measured it was about 1.4mm after coming off the standard is just over a mm.Also fitted a new Keihen FCR 41 what a difference the front end comes up a treat!! Night & day difference the bike carburates smoothly at constant throttle & accelerates much better than the non pumper standard Dellorto.

 

[jmics19067]

Let me rephrase what I posted earlier, I had no apparent ill effects of the head gasket sealing and or head bolts coming loose /stretching or anything like that. Now my back yard engineering of a high compression combustion chamber had a little bit to desire.


I tend to believe that since the head bolts are used strictly in a clamping tight situation, the torque value for the bolt to remain tight would be appropiate. How much the gasket will crush is really not much of a factor to the bolt as long as it crushes enough to seal . Now the expansion rate of the aluminum gasket may play a bigger role, but I would think that the percentage of the gasket thickness compared to the thickness of the head is relatively minimal. Possibley even smaller than the accuracy rate of your torque wrench at which case the point is moot. This is of course if my assumption is correct.

I have changed a few head gaskets ; old steel oem auto to new aftermarket composite, different oem composites for service updates and have seen no service update for a different head bolt torque , plus had decent luck on the one I made as stated earlier.Nothing concerning aluminum though, I can only assume and would hope that the tuner/ designer of the kit you purchased would give you an update if a change was needed.

As a mechanic I only have to figure out what is out of spec and then basicly follow directions putting it back together. If there is no change in directions there is no change assembly procedure. It does interest me greatly at the possible problems associated with any change. I don't mind jumping into a conversation sounding like a numbskull as long as I walk away with more knowledge than I started with ;)