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MG MGB Technical - Re-torqueing the head gasket.

I have just had some cylinder head porting work done on my 1950 cc 5-bearing engine and, as part of the process of re-fitting it, I replaced the cylinder head gasket.

I have ARP head studs and I used a Payen head gasket and torqued it down to 54 ft-lbs ( recommended by Peter Burgess).
Peter has told me before, that the Payen gasket shouldn't need re-torqueing, but I decided to check them yesterday after the engine had done over 100 miles.

Most of the head nuts were fine but I found that the nuts at each end (10 and 11), rotated by 1/8th turn before the torque wrench clicked.

When I removed the cylinder head a few months ago, I had noticed at the time that these same two nuts were a little looser than the rest.

Has anyone else ever come across this before?
Should I be worrying about it?

Cheers
Colyn
Colyn Firth

Did you back off before tightening?

When was your torque wrench last certificated, is it kept in a velvet lined padded wooden box?

I don't really know but thought you need to back off to check torque which always seemed a bit risky to me as upsetting the seal you already had.

Nigel Atkins

Hi Nigel
my torque wrench is pretty much brand new, I bought it new a couple of years ago to replace my old beam type wrench that was the more basic kind that had the long pointer and a vernier scale alongside the handle.

I didn't back-off the head nuts when I re-torqued them, all of the nuts were fully torqued up when I re-checked them apart from the two end ones, which, as I mentioned, turned approx 1/8th of a turn before the new torque wrench clicked.

Maybe it is something specific to this one particular cylinder head. I will re-check those two end nuts again in another 100 miles or so,

Cheers
Colyn

Colyn Firth

Head nuts should be backed off 1/4 turn before retightening - otherwise stiction will give a false reading. For all you know the other nuts may be exactly the same and will retighten + 1/8th turn.

The backing off and retightening is done one nut at a time in the correct order.

But Peter is correct, Payen composite gaskets do not need to be retightened unlike steel or copper ones.
Chris at Octarine Services

With alloy heads like the Derrington or MSX it is usually recommended to re-torque after a couple of full heat cycles? Opinions?
Mike
Mike Ellsmore

I do Mike, on either cast or alloy, usually as you say after a heat cycle or two and again after a few hundred Klm's, Important to back off first then retension ,one stud at a time and in normal order.I only just loosen them enough so that I know they're going to move, just a slight crack off is enough then pull up to tension very slowly.
The only time I don't retension is if it has a MLS gasket, they don't usually move at all
cheers
willy
William Revit

This thread was discussed between 10/06/2020 and 12/06/2020

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