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MG MGB GT V8 Factory Originals Technical - Cylinder head torque
|My 3.9 Rover manual suggests 90 Nm - This is a compo gasket - any ideas ?|
|What was the old gasket? My factory V8 are tin shim, as was a pal's Rangie. He fitted a compo and performance was noticeably compromised, so took them off again and fitted a tin shim and it was fine. AFAIK the torque is the same, but the process for compo is a lot more involved. My Scimitar GTE used compo and I was advised to scrupulously clean both surfaces, and apply no sealant such as Wellseal which I use with tin shim. If the old gasket was a compo it should have bonded to the head and block which will mean careful scraping first. Torque down in the usual manner i.e. correct order and tightening slooowly until the studs finish stretching/gasket compresses. If you tighten too quickly i.e. straight up to the figure and stop it will detorque itself slightly. *Don't* add any coolant, and run the engine until quite warm but not hot. Leave to cool overnight. Next day retorque by backing off to get the nuts started then tightening to torque as before. Fill with coolant but don't fit the cap, run up to near normal temperature, switch off and again leave to cool overnight. Next day retorque again, top up coolant and fit radiator cap, and away you go. That worked fine on the Scimitar, and I used the same process when changing the compo head gasket on a midget 1500, the previous compo only having been on a few weeks after just having been slapped on, and had gone again.|
|Paul - thanks - the old one was compo too - I am sure this is good advice but I cant imagine the factory was so fastidious - it was impossibly tight to remove 'though so I suspect it was much tighter than 90Nm.|
|Don't torque down the outer 4 bolts beyond 15 ft/lbs.|
|I left the outer four bolts out completely. Seven thousand miles later there is no sign of trouble. I also did not re-tighten the bolts once the engine had been run for a while. In fact in over 40 years of amateur engine work I have never re-tightened cylinder head bolts on several types of engine, and it has never been an issue for me.|
|Indeed, only a low torque on those odd four as they are likely to *cause* distortion. Didn't retorque my tin-shim gaskets either.|
|All good advice, for which I am grateful. Mine seems to be one of the last of the pre-serpentine but without the outer row of bolts. I fear that despite following Paul's advice reasonably closely, it is blowing. Will check tomorrow.|
|OK; tightened down very carefully - and running well. Thanks for the help.|
This thread was discussed between 10/10/2010 and 19/10/2010
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