Head Bolts retensioning/torquing

A friend of mine, who is ex Landrover, has said that if he suspected a HGF he would tweak the headbolts ie tighten them a bit more - say 20 degrees. I have also read of people doing the same.

So, out of interest, are the headbolts at maximum tension when the engine is hot or cold ?

it has been suggested this used to happen in rover workshops, they used to drain coolant as well, run engine and then tighten bolts

hot

Not always going to give you an answer though. If a gasket has failed between a cylinder and a water gallery (for example) and had been 'blown open' all a tightening of the head will do is compress it down in that state, it won't always close an open gap..... if that makes sense.

jamesmartin said:

hot

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Presumably the head/block expand more than the bolts.

So, as an experiment, I tried giving the head bolts a tweak. I was amazed that it was pretty easy to give them about 20 degrees with a cold engine. The effort required felt less than when I originally torqued them. I am now wondering if I should of backed them off to just below the initial torque setting & then followed the normal procedure. With the various components it does suggest that the MLS gasket compresses a lot.

and you will run it and let it cool and you will get another 20 degrees, and all you are achieving is stretching the bolts

freelance said:

and you will run it and let it cool and you will get another 20 degrees, and all you are achieving is stretching the bolts

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If the bolts stretch that easily then it may be a cause of some of the problems. There are a number of manufacturers of these bolts & it makes me wonder if they are all to the same spec.

It's not that I got another 20 degrees. It's the fact that it required surprisingly little effort compared to the original torquing.

no point at all in re tourqueing head gasket bolts. some bolts are stretch bolts and require a torque and a degree tighten

i you tighten them down again all you will do is at best stretch the bolt or worse strip block threads

head gaskets have been made for about the last 15 years that require no re tightening once fitted. some older ones did require a re tourque after 30 minutes or so but that was it

I fully understand the principle of stretch bolts. I was just very surprised that the bolts turned quite easily.

Perhaps you had an extra weetabix this morning