Hot tightening cylinder head nuts?

[Graham Barker]

I have just given my Ruby a short run in the garage after replacing the cylinder head.  I seem to recall some people mentioning to retighten the nuts while the engine is hot.  is that right?

[Greig Smith]

No cold is best, things expand when they are hot and shrink when they are cold, so a hot torque will always yield a lower figure when the motor has cooled

Aye
Greig

[Andy Bennett]

And as has also been said, following advice and with new gasket I reset overnight without a run, then after a run, then reset again. I did mine 3 times over about 300 miles (I did 20 miles, 100 miles, 300miles) and each time they took more tightening.

Andy

[John Mason]

I seem to differ from everybody else. I was always taught to relighted when hot and can remember being told some 60 years ago that the head studs expand more then the head when hot so re tightening hot makes them correct for a normal heat for a running engine. I have never had any problems with 7s or any other engines. No torque wrench use in those days.

John Mason.

[Terrytuned]

Graham cast iron heads hot alloy heads cold 20ft lbs.
Terry.

[Chris Garner]

Didn't I read somewhere that when installing an alloy head, wrap it in newspaper and put in the freezer, telling the wife it was a block of ice cream?
Once frozen, assemble it on the block and tighten down, starting the engine fairly soon afterwards to counteract the condensation. ( remove newspaper first!! )

[Graham Barker]

Thanks for the advice albeit conflicting.
In an attempt to resolve the conflict for my cast iron head, I tightened the bolts to 20 ft - lb while hot after a 2 mile run. When cold I checked to see what torque was required to budget the nuts. When cold, I needed just over 20 ft-lb to make the nuts move.
My conclusion is that hot tightening gives about the same result as cold tightening on a cast iron head.

[Andy Bennett]

Do check again after a few hundred miles. With the gasket settling and everything 'relaxing' a couple of my nuts were down to 16 after 300 miles. When I checked again after about 700 miles it hadn't changed again.

[John Mason]

Yes I agree with Terrytuned cast iron heads hot alloy heads cold 20ft lbs.

John Mason

[Chris KC]

Cylinder head nuts should be tightened cold. Then run the engine up to temperature, let it cool down again, and re-tighten, cold.