Head Re-torgueing - Hot or Cold?

[ford3]

ok i will put my 2 cents worth in, when torquing head hot your torquing an engine that has expanded metal, metal gets hot it expands, so when it cools it contracts so when that happens you lose torque value, if you torqued the head to 55# hot, and the the heads contracts when cold you will no longer have 55# torque

[Russ/40]

Originally Posted by ford3

ok i will put my 2 cents worth in, when torquing head hot your torquing an engine that has expanded metal, metal gets hot it expands, so when it cools it contracts so when that happens you lose torque value, if you torqued the head to 55# hot, and the the heads contracts when cold you will no longer have 55# torque

That may be, but how do you know that? Lets just limit it to iron heads for discussion. Who's to say the stud length doesn't shorten when cooled, increasing torque.

[Joe K]

Originally Posted by ford3

ok i will put my 2 cents worth in, when torquing head hot your torquing an engine that has expanded metal, metal gets hot it expands, so when it cools it contracts so when that happens you lose torque value, if you torqued the head to 55# hot, and the the heads contracts when cold you will no longer have 55# torque

The values of expansion for cast iron are 6.0 and for steel 7.3. (units are the same but don't matter) Thus when cast iron and steel are heated, the steel expands more by about 21 percent than the cast iron.

Ditto in reverse for contraction. Steel contracts more by 21 percent.

Thus if you torque while hot, as the assembly cools, the stud tension actually INCREASES as the cast iron shrinks less than the steel.

The difficulty herein is if you torque (tension) the stud hot to near it's yield point - which is a point of permanent deformation - as it cools that yield point will be exceeded and the stud will take on a permanent stretch - and doing as you say, relieving the tension. (releasing the torque)

So the lesson to be learned from this is you don't tension your studs up to near the yield point - you size their diameter to maintain a certain compression on the gasket without going that close to potential failure regardless of your temperature range.

Joe K

[tbirdtbird]

Re-read this again and again....

"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."

[Mike V. Florida]

Originally Posted by tbirdtbird

Re-read this again and again....

"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."

How about the company that produced millions of the engines and put the tightening instructions in writing to each and every dealer?

Whose foot is shot!

[hardtimes]

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Originally Posted by Mike V. Florida

How about the company that produced millions of the engines and put the tightening instructions in writing to each and every dealer?

Whose foot is shot!

'how about' ...that one is easy ? Well, that company , back 80 some years ago ...was writing (simple) instructions for MILLIONS of people , for the most part with rudimentary education and in lots of cases with no/ zero education/experience with cars/engineering ! Think about that. How would YOU have written such for such ? Hmm, explained the yield point etc,etc...yeah ?

WE are very lucky these days to have association with engineers/hands on experienced race car members on this forum. They know what Henry's engineers knew , back when, and more now...IMO. AND, they take the time/effort to try and share their knowledge with US in our hobby.
Like any other thread...don't like or agree with subject...go on by,eh !
But, in this case , at least, you can not say that it is not germain.

[Mike V. Florida]

Originally Posted by hardtimes

'how about' ...that one is easy ? Well, that company , back 80 some years ago ...was writing (simple) instructions for MILLIONS of people , for the most part with rudimentary education and in lots of cases with no/ zero education/experience with cars/engineering ! Think about that. How would YOU have written such for such ? Hmm, explained the yield point etc,etc...yeah ?

.

We are talking about tightening a bolt not designing an engine. I don't think years of training, schooling and race experience is necessary for twisting a wrench on a nut. Maybe some posters here like to think that, I don't.

The bottom line is it makes not a pile of dog droppings if it is done hot or cold as long it is done with all the nuts at the same amount and kept that way.

[1931 flamingo]

DITTO, all the same and no seepage. FWIW The car didn't come with a torque wrench in the tool kit either.
Paul in CT

[Ron/IA]

Mike V. Florida hit the nail on the head when he stated - "all the nuts at the same amount and kept that way".

I recently had a reply from Larry Brumfield; he stated the following: "Always torque and retorque cold on a flat head. You want the most accurate torque possible which would be harder to achieve with the unwanted friction created by heated or hot threads."

That certainly makes sense to me, and that is what I am going to do.

Thanks everyone for the very interesting thoughts.

[Gary WA]

Originally Posted by Ron/IA

Mike V. Florida hit the nail on the head when he stated - "all the nuts at the same amount and kept that way".

I recently had a reply from Larry Brumfield; he stated the following: "Always torque and retorque cold on a flat head. You want the most accurate torque possible which would be harder to achieve with the unwanted friction created by heated or hot threads."

That certainly makes sense to me, and that is what I am going to do.

Thanks everyone for the very interesting thoughts.

I 100% agree with Larry as I stated above spent 45 minutes discussing it with him a few days ago,on Ahooga site. Its all there to read under Chat. Thanks Ron,