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Head bolt torque value

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Hello to all here,

I have read through a lot of posts in the search fields and there are many thoughts and posts on this subject about "torque values and bolt categories" for the 

early 20"s cars.

Can anyone please recommend a suitable torque value for the Big 6  7/16" head bolts/studs ?

I don't want to pull through and destroy a good thread in the block with too high a "listed torque value", for a modern Grade 8 stud, that this old machine didn't have.

What is an acceptable lower value I can use ?

Thanks in advance for any help here.

Roger 

Brisbane, Australia

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Roger

was told to use contemporary bolts on my 1927 Chevy I am thinking it was like 65lbs will verify, they do stretch so probably would be afraid to use modern grade 8 but in a pinch might.

Ken

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On my 1925 Pierce 80 with 7/16" studs and iron head I use 55 ft/lbs.  Be careful of modern replacement nuts:  I bought some from Fastenal which were made in China and they are too loose on the threads.

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I also check them every season at least once to make sure they have not loosened or stretched.  also the spark plugs.

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Agree that checking torque is important, ESPECIALLY if your head gasket is a repro with a plastic vs. asbestos center. Re-torque only when cold, to minimize stretching, after some heating/cooling cycles.  With repro sandwich gaskets, it usually takes at least four re-torquings in the first 200 miles before it's finally snug.

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Remember you are dealing with old metals, probably not very strong. The bolts can pull out of the block same as the nut can strip the bolt. They did not have torque wrenches back then either.

 

The internet will give you plethora of values. Don't go above grade 5, e.g. http://www.repairengineering.com/bolt-torque-chart.html

Edited by Spinneyhill (see edit history)

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In a technical post on the SDC forum Gary Ash posted a detailed analysis of differences in expansion properties of aluminum and cast iron.  It is one of the most interesting threads I have read on any of the forums that I follow.

 

One of the things that caught my eye was Gary's mention of using grade 2 bolts as head bolts.  Are such things still available?  I'm about to install a replacement head on the 250 cubic inch straight 8 in my '35 Commander.  Any comments on re-using the original head bolts? Thanks.  Tom

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I reused the head bolts on my 1930 Pontiac four times with no problem (usually torqueing them to 60 pounds).  The next time I broke three of them at less than 40 pounds.  I replaced them all with standard grade five bolts and have had no trouble since.

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Clearly, 60 ft-lbs is too much for the original head studs and their fatigue life has been exceeded with a small number of cycles. If you use torques recommended for Grade 2 (or perhaps Grade 5) in the tables such as the one I pointed you too, you should be able to re-use them many times. I think they also used soft compressible gaskets originally?

Edited by Spinneyhill (see edit history)

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