Head Re-torgueing - Hot or Cold?

R

Ron/IA

Well-known member
I have been reading with interest the discussion on torqueing the Model A head in the post titled - "hmmm...wet head stud".

The majority consensus is that re-torqueing the A head should be done after the engine is thoroughly warmed up. My limited engineering brain agrees with this. But, I began thinking about what I have read in various publications, and began wondering.

The Service Bulletins state the engine should be hot. The book titled "The Model A Engine" by William H. & Paul H. McRee states hot also. So, I began to wonder how the "cold" re-torqueing method came about, and I discovered one such item (there are probably others).

The "modern silicon gasket" instructions state the engine must be cold before re-torqueing. In fact, it is recommended the engine set over-night before re-torqueing.

I am not trying to cause a big discussion on "hot vs. cold", but why is this statement being made, and are there other manufacturers or publications that state re-torqueing cold also?

Sorry, I just have a curious mind.
 
Ron, your interest is very much justified. I think the clamping force of the cold engine is higher if the head was torqued hot. This calls into question the torque specification. There should be a spec for cold and another for hot.
 
There should be a spec for cold and another for hot.
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The only thing that separates a "cold" torquing number and a "hot" torquing (different) number is the torque value. That given a stud that does not go to yield during cool-down.

If a stud does not go past the yield point in stretch at either thermal condition then there is no difference.

I have not done the mechanics of materials examination to determine if 50 ft-lbs (or whatever amount) will bring a head stud into that "yield" territory as it cools. But if it does not (likely) then there likely does exist a cold torque (tension) value that would work equally as well.

One imagines that the company that sells the silly-cone gaskets would also be one that might sell replacement studs? That way they could be sure of not having the studs go into yield. And you're buying an "engineered" sealing system. (As the VW aftermarket head stud providers are wont to advertise.)

Or maybe the design is that they DO go into yield during cold torquing and any relaxation during heat up (probable given cast iron/steel thermal interplay) is accomodated into the design? Think the VW example I cited in the other thread.

One use only studs for this latter case though.

Joe K
 
The model a engine being 80+ years of age has been fitted with many different cyl. heads and gaskets. When torqueing head nuts the very best advice is to follow the manufacturers instructions.

Chet
 
Cold!!!!! Just had a long discussion with the man-Larry Brumfield on proper head torque method. all heads! on Ahooga Chat! check it out.
 
Growley bear said:
The model a engine being 80+ years of age has been fitted with many different cyl. heads and gaskets. When torqueing head nuts the very best advice is to follow the manufacturers instructions.

Chet
Click to expand...

The model A torque "specs"

Oil pan etc-----snug
Head nuts-------tight
Axle nuts--------good and tight

Snug: as tight as you can get a Tee handle wrench with 1 hand

Tight: as tight as you can get it with the wrench

Good and tight : use a pipe on the wrench
 
Very interesting! We are now seeing comments that call for torqueing cold as well as hot.

However, I agree with JoeK that values used for torqueing when engine is cold would be different than values when hot.

I need to do a little checking; a member in our club had to torque the silicone gasket many times before things settled down, but I don't know if he was re-torqueing cold or hot.

I am also going to research some gasket manufacturing data. I'll let everyone know what I find.

Edit Note - I just read a FelPro paper that stated re-torqueing the head bolts with the engine hot. Does anyone have other manufacturer's data?
 
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I know that if you overheat the engine you better recheck the torque. Last summer my lower steel pipe developed a pinhole after the vinegar treatment and I didn't realize my coolant was low until I heard it steaming. When I got home I found several head nuts were quite loose.
 
Either way, new gaskets settle or compress, it maybe heat but it could easy be use too or it's both. Best to follow up with whatever you choose, I've done it both ways, both work. It's good to check them after storage too.
 
"Edit Note - I just read a FelPro paper that stated re-torqueing the head bolts with the engine hot."

Care to post that link for all to see?
 
 
Heh. I see the "warm" recommendation for cast iron head and the opposite ("cold") for aluminum heads.

This corresponds to the GREATER thermal expansion of aluminum (12.0) compared to steel (7.3) as opposed to the LESSER thermal expansion of cast iron (6.0) compared to steel.

So based on my recommendation earlier to torque heads "warm" to achieve a stud tension that will not have possibility of relaxation under thermal cycling, one should torque aluminum heads "cold" to eliminate the possibility of relaxation on thermal effects.

Well, it seems I'm in agreement with Fel-pro on both accounts.

Joe K
 
I always torque the head cold . Start the car up with no water and run it until engine is warm [does not take long] .I let it cool and re-torque. This i do with the old repro. copper clad head gasket.Works for me.
 
SIMPLE ANSWER...Please follow the instruction of you engine rebuilder to adhere to your warranty....If off warranty follow the instructions of the gasket manufacturer
 
msmaron said:
SIMPLE ANSWER...Please follow the instruction of you engine rebuilder to adhere to your warranty....If off warranty follow the instructions of the gasket manufacturer
Click to expand...

Right on Mark!

If we want the support of the suppliers/manufacturers we best follow their installation instructions.

Good Day!
 
msmaron said:
SIMPLE ANSWER...Please follow the instruction of you engine rebuilder to adhere to your warranty....If off warranty follow the instructions of the gasket manufacturer
Click to expand...

That could also be said as, "follow the instructions of the HEAD MANUFACTURER".

And the best answer to that is, dream on.

That's why 2 of the best head manufacturer's that ever hit the scene no longer make heads.

Who is to blame??
The simple minded person that thinks he knows more than the design engineers who not only spent 5 to 7 years in engineering school but also had actual on track racing experience to add to the development of the product.

You guys shot yourselves in the foot.
 
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