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MG MGB Technical - Cylinder head nuts torque wet or dry

The torque for the cylinder head nuts is 45-50 ftlbs according to the manual but it does not say if it's wet (threads oiled) or dry (threads dry). I've also read from a reliable source that Payen recommends torquing the nuts to 54/55 ftlbs and not retorquing them after 500 miles.

I'm about to reinstall my cylinder head after replacing a seeping head gasket so any comments would be appreciated.

Andy

74 MGB GT.
Andy Preston

Andy,

FWIW

Mine is an 18GG in a 69 build car. Street use with mild spirited driving.

I used a Payen as well. I torqued in 3 steps and set my torque wrench at max to 53lb (working on the theory that at +/- 4% accuracy I would be somewhere between 50-55, ie between upper manual and the Payen figures). I followed the Payen recommendation and did not disturb anything by attempting a re-torque.

I lubricated the stud threads with a little engine oil on advice, from several still practicing mechanics, that that was the convention in engine shops through the era of these engines.

Some 7 years later all is well.

Regards

Roger
R Taylor

Unless otherwise stated, the threads should be lubricated with engine oil. If you are using the APT studs, they give two torque specs, one with engine oil and one with their special lubricant. Cheers - Dave
Daved DuBois

Thanks Roger and Dave; engine oil it is then on the studs prior to torquing. I'll torque to 53 and pray the studs don't snap.

Andy
Andy Preston

Andy I dont like going over 50lb because there is nothing to gain and I feel it can add to the block distortion at the base of the studs. I use a Payen gasket and ARP studs at 50lb on my supercharged engine on nine pound of boost and no problems in many years.. Make sure you counter sink the stud thread holes about .030".
Denis
Denis4

The threads on the studs in the block, and the threads on the nuts must be clean and free running. If you can't screw them in with your fingers they aren't good enough. All threads must be oiled. It is a good idea to countersink the stud holes in the block face a tiny amount, as Denis mentioned. There is no point going above the recommended torque, and personally in over 40 years of engine work I have never re-torqued a cylinder head and have never had a problem as a result.
Mike Howlett

Thanks for your advice guys. When I removed the head due to minor coolant seepage into #1 and #4 I found 3 long head studs were loose in the block and I could remove them by hand. So this time I used some blue loctite thread locker (medium strength) on the stud end in the block. Perhaps I shouldn't have done this. When I rebuilt the engine 20K miles ago I oiled both ends of the studs and as I said 3 of them were loose.

Thanks Andy
Andy Preston

The studs would have been loosened by you removing the nuts on the top of the studs. That's absolutely fine and shows the threads are nice and free. They couldn't be loose before you started undoing the nuts - that's impossible. When you torque the head down you are tightening both the top thread with the nut on it and also the bottom thread that screws into the block. You can't do one without the other. That's why it doesn't matter if the studs are just put into the block finger tight. I don't suppose using thread lock will do any harm, but it simply isn't necessary.
Mike Howlett

And don't torque the studs into the block, you can crack it. They *should* only be finger-tight.
PaulH Solihull

Thanks guys I put the head back on today and torqued the nuts wet to 50 ftlbs and didn't snap any studs. So far so good. I'll see if I can finish tomorrow and be back on the road. Paul it was good to hear from you again.

Andy
Andy Preston

Blocks are very vulnerable to cracking between the stud and pushrod hole on that side of the engine. I have also seen the long studs rip up through the hole. Most of the affected engines had been torqued past 50 at some stage previously, usually by people trying to get a better clamp on a competition engine.
Paul Walbran

Hi guys I've got over 200 miles on the car since I replaced the cylinder head gasket and all is going well. The car drives strong and there's no coolant leaking.

Funny thing though is that the running temperature has dropped around 10 F and the oil pressure has incresed by around 5 psi. I can't think why that would be. The engine used to run fairly hot before and I even added an electric fan to assist in cooling and now is doesn't come on.

Andy
Andy Preston

Andy, it's winter!
Art Pearse

Hi Andy.

Lower temp will give higher oil pressure, with the V8 idling I can see the latter going down as the former goes up before the fan cuts in! There can be all sorts of reasons why an engine runs a bit hot, but way short of actual overheating. Again on the V8 I started losing coolant because of air bubbles (not combustion gases), and eventually I had the heads off but it seemed to be changing the water pump that stopped it. After that it ran cooler on the gauge, and differently while it was warming up, compared to before I had the coolant loss.
PaulH Solihull

This thread was discussed between 29/01/2013 and 07/02/2013

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