re-torquing a head gasket

[450 Farmall Hooker]

On a 450 farmall, how many times should you re-torque the head? Is there any reason or benefit to do it more than once? How hot should you get things before a re-torque?

 

[BushogPapa]

Run it until it is FULLY "Heat-Soaked"...

You want the block, Head AND the Head Bolts to be up to Full operating temp while you re-torque..

Ron..

 

[buickanddeere]

How do all the brand new machines run thousands of hours and 100,000's of thousands of miles without a re-torque.

 

[Anonymous-0]

(quoted from post at 11:32:26 08/05/12) How do all the brand new machines run thousands of hours and 100,000's of thousands of miles without a re-torque.

cause the manufactures know everything grows with heat i have found some here that think one grows more than the rest of the items that complete the build

 

[CoopertownBob]

(quoted from post at 14:32:26 08/05/12) How do all the brand new machines run thousands of hours and 100,000's of thousands of miles without a re-torque.

That's a good question and one I've often wondered myself, though I don't really know anything about how it is done. I know there are such things as so-called "no re-torque" gaskets made, but I wonder how they work.

Only things I can come up with on my own is either the manufacturers over torque stuff on purpose, knowing exactly how much over to go so after the first run in it levels out where it belongs, doesn't sound very likely to me though. Another idea is that the engine assembly is farmed out to another plant that runs in the engines and then re-torques them, a very likely and easy to do possibility. The last thing I thought of is maybe they heat and pre-compress their gaskets before installation. Like I said, I don't know but have wondered, I do know that if I don't re-torque the head gasket on a brand new install it will be loose, and sometimes loose enough to cause problems.

How about it, anyone on here work for a tractor or auto manufacturer that knows how this works?

 

[Rwolfejr]

At install I go through the torque sequence a bunch of times adding a little torque each time until reaching the recommended torque. I do two re-torques on my diesel Deere and haven't ever had a head gasket go. I assemble and torque. Run a little bit and let cool. Run a little again and let cool. Then run it up to hot and let it cool... then do a re-torque. Usually that first re-torque I'll get maybe 2 or 3 of the nuts that'll move a wee bit. Then run it through a few more heat and cool cycles and re-torque. One time in the last three head installations I had one nut that moved a breath on the second re-torque.

I don't buy into the re-torque them hot theory. The coefficient of expansion of all the ingredients is so close to the same that any difference is negligible... especially at a temperature difference of only about 200 degrees. Linear expansion of cast iron is .00000655 inches per inch of length per degree. Linear expansion of carbon steel is .00000633 per degree. If anything... with the cast expanding slightly more than the studs you'd be "less tight" torquing hot than cold. Technically the cast iron would be a breath from a gnat bigger than the stud and therefore you'd be tightening on something that will shrink that breath of a gnat more when it cools.

Not enough of a difference in expansion to matter. Too many other variables of much greater significance. Thread condition... head and block surface... possible gasket thickness variation? It would be more probable to have issues from those things than temperature at the time of the torque.

In my opinion the factory doesn't need to re-torque for a few reasons. I'm sure they step the torque sequence which is very important to ensure all studs are stretched equally. All of the threads are sparkly clean so you don't get errant torque readings because of some rust or poor surface finish causing extra drag and giving a false torque. And... The bolts are brand spankin' new and have never been stretched before.