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MG Midget and Sprite Technical - Torquing Heads

I know that there are probably dozens of threads on the archives about this subject. However, I find searching the archive a pain in the A*%@. 3000 miles since the HG was changed and I've been a bit tardy in not re-torquing it, I know don't shout. I will be changing the rocker cover as part of the work I will be doing on my breather set up, so should I re-torque then. if so what is the best way to go about it. Loosen the nuts in reverse order and re-tighten, or loosen and tighten in order one at a time?. Related question. Should I change the rocker shaft while I'm about it?
Pete Ottewell

personally I'd not want to loosen anything. A quick buzz round with the torque wrench to check tightness and that's enough. Others may disagree, but my opinion is that it can upset the gasket to be slackened off and re-tightened.

You don't need to replace the rocker shaft unless it's worn, though you could check the valve clearances while you're in there.
Rob Armstrong

Problem with that , Rob, is that the nuts will stick to some extent so that it will need more torque to get them moving even though they may be under-torqued. Sorry that doesn't explain it well, but I know what I mean!

I slacken just one at a time, and re-torque to the correct setting before moving to the next one. And follow the "spiral sequence" normally used on a head. The gasket won't be disturbed if only one nut is loosened at a time.
Guy Weller

Pete,

Well, to break the tie, I'll second what Guy said, and for the same reason. Unless they are very loose, you have to free it up to be able to torque it again. And, yes, only one at a time.

You should be able to slide some of the rockers to one side so that you can check the underside of the rocker shaft for wear.

Charley
C R Huff

x3, what Guy and Charley said, to properly torque the head you slacken and re-torque them, one at a time.

The amount of slacken is small, like 90 degrees. Just enough so that when you re-torque the nut is slipping against the washer.

If one were to really worry about causing a gasket seal failure, the coolant could be drained first (the only thing really likely to get in there, in the brief moment of slackening), but not really needed.


Norm

Norm Kerr

I've said it many times before on here and on the MGB board, but why re-torque them at all? In over 40 years of messing about with cars I have never re-torqued a head, and there has never been a problem. It might be necessary with certain types of head gaskets, but the common composite ones don't need it in my opinion. I think you are asking for trouble by doing it. But if you must re-torque, it is essential to slacken the nuts off to make it work, and the nuts and studs must be very free in their threads.
Mike Howlett

I must admit that I am a bit puzzled when it come to re-torquing. I have had 4 new cars in the passed 10 years, none of them have had the head re-torqued as part of their first service. I do have this nagging thought in the back of my mind though that it's 3000 miles since it was done. I suppose that I will get responses in both camps. Do I temp fate either way?
Pete Ottewell

Pete,
The explanation on the modern cars may be that they use stretch bolts, whereas the A series engine doesn't (well, not intentionally!. Maybe modern technology of stretch bolts maintains tension rather better?

My guess is that retorquing isn't at all essential, although I do it. But for those of us who like to feel manly or useful, it is something to do which maintains the illusion of great skill and knowledge and the mystique of keeping these "older cars" on the road.
Guy Weller

Hmmm... I retorqed the heads on my cars but I used to just reset the wrench up 2 pounds. I never thought about initial drag once they were tight. The mgb manual states 45 to 50 lbs cylinder head stud torque.
I would tighten to 45 and retorque to 47 maybe later end up at 49. You guys really think it makes that big a deal to backem off? I think that would cause a problem. Im just asking, most old timers I were around would just add a pound or 2 and call it good.
Steven Devine

The risk with going higher on the torque is that leaks are actually more likely to occur when they are overtightened (the crush rings get squashed beyond their working range).


Norm
Norm Kerr

I wonder if doing a hot re-torque... would better to not back off.... just a thought

that said ... ive always backed mine off 1 at a time as per ... the hand book

que FRM

prop
Prop and the Blackhole Midget

Im pretty sure Im still in the spec range 45 to 50
Steven Devine

I'm going to have to do this after replacing a blown head gasket on my 1500. I didn't retorque last time, and I think that it contributed to the failure. However, I think you should retorque very soon... just as soon as the engine is up to temperature - once the engine has gone through a heat cycle, everything will shift around and settle and thats when you want to retorque IMO.

I have a friend who races triumph spitfires, he says he overtorques standard studs to 60 (book says 50) and he does it when hot. I'm not sure I like this at all.

C L Carter

Overtightening head bolts beyond the specified setting, either at first fitting or at a subsequent re-torquing, does no good at all. It distorts the fire rings which are the part of the gasket that contains the explosion. And it actually reduces the clamping effect on the fire rings by spreading the main clamping force over the much larger surface area of the plain part of the gasket. Same force over the larger area = less pressure in lbs/sq inch on the fire rings.

It is counter-intuitive. At the moment one is tightening it all up there is a real temptation to "add a bit" for good luck, just to make sure that the head is clamped down tight. But that is not the way the thing is designed, it won't help and could well increase the possibility of HGF.

If you are in doubt, read this Calver article about it:
http://www.minimania.com/article/1227/CYLINDER_HEAD_-_Torque-down_and_head_gasket_problems

or here:
http://tinyurl.com/bs2cxzx
Guy Weller

I have been playing about with A series engines 850cc to 1275cc for years and when coper asbestos gaskets stopped that's when I stopped re-torquing heads. I don't believe there is any need with the modern gaskets. My last overhaul has now done 14000 miles and never been re-torqued, no doubt it will fail next week just to prove me wrong.
Still passed MOT this morning no advisories.

Mike
Mike J Pearson

I think what Steven describes would be effective as long as the nut is actually moving. But, I think you can torque a head to 50 ft lb for example, then drive a few hundred miles, put a torque wrench to it, pull it to 50 ft lb, and find that the nut does not move.

However, if you then mark the nut with a paint stick, slack it off about a quarter turn, pull it to 50 again, and you will likely see that the nut is tighter than it was before. If the nut ends up exactly where it was, you didn’t need to retorque, but if it is tighter, then you did need to retorque.

I suspect this is due to the difference between the static and kinetic coefficients of friction. That is, you usually have to push something harder to get it to start sliding than to keep it sliding after it starts.

Also, I don’t think the people in the retorque vs non-retorque camps will gain much ground trying to convert each other. I intend to stay in the retorque camp.

Charley
C R Huff

There's a difference between copper/asbestos gaskets and the later coated composite type. The early ones need retorquing after the first heat cycle and then again after a few hundred miles. The later coated gaskets are much more forgiving, and were developed along with better quality nuts and studs to be retorqued once after the first cycle, and then left alone - which was all part of BL's policy to lengthen their service intervals.
F Pollock

I always stayed on the fence on this one too, unless suddenly the damn thing blows a head gasket... Ive got a 1964 mgb 3 main in the A. It wiped one out last year, after 10 good years of service. I never retorqed it...In all that time. Then bamb it was gone. I spent the forth of july doing the head gasket. It went between 2 & 3 like they always do.
I know Ive driven it hard a long time but well why would that go first?

Its been fine since...
Steven Devine

I'm with Charley- our engines are specified with a working torque figure, not an installation torque figure like modern engines.

Studs on modern engines are more elastic, mainly to be able to cope with the expansion of an alloy head, but also simply because they're made of better steel. Conveniently, this means the manufacturer can specify a torque setting that accounts for the gasket's initial crush, but still has enough spring to hold the engine together. Mr Toyota Factory Worker can torque that 4AGE engine to 88ft.lb with confidence, knowing that the engine only needs 75ft.lb to be reliable, and the studs give way at 100ft.lb.

BL's figures are closer to what the engine needs to run reliably, based on the idea that you'll be re-torquing the head studs like it says in the workshop manual. Because the studs aren't very springy there's less leeway there, so it's important to run the torque specified even after the gasket has crushed.

Which brings up Charley's point: Install a new head gasket. Heat cycle it a couple of times. Note the position of a head nut. Slacken it 1/4 turn and then re-torque. If you end up exactly where you started, then your studs are at the correct torque and a retorque wasn't needed. Well done you, I'm wrong, let me buy you a beer. But if you end up 1/8th turn tighter, then your studs were looser than the factory specified, and you should retorque the rest.

How loose is too loose? I don't know, there's obviously some leeway there. But for the sake of 5 minutes with a torque wrench I'm going to continue to make sure my torques are spot on.

(Oh, and too tight is as bad as too loose- the stud may cease to act like a big spring (elastic deformation) and start behaving like a big stick of plasticine (plastic deformation). Re-torque when the head is cold and stick to the workshop manual's recommendations.

Growler

hi, your topic is torquing heads,,....wern't they a pop group back in the 70s????
rgds tony
a boyle

" ---- torquing heads,,....wern't they a pop group back in the 70s????"

No, you're thinking of "max headroom", from the eighties. :)
Lawrence Slater

Tony, only 21 posts before someone was on my wave length. We're on a road to nowhere.
Pete Ottewell

Excellent, These last three Posts were the only ones worth reading! As self proclaimed judge of this one thread, you last three get a 9 out of 10. Please buy yourselves a beer, and drink it. For a Job well done! From Massachusetts! I solute you!
Steven Devine

Thanks Steven, nothing wrong with injecting a little humour eh :).
Pete Ottewell

hi all ..i have drunk my beer....
Remember our old mate booker t and his mg ????
where will this thread end ? on the road to nowhere in an mg
rgds tony
a boyle

I intend to solute myself in beer tonight.
Pete Ottewell

I replaced a gasket on the head of my old VW Golf diesel and the instructions were to torque all up to 20 or 30 ft lbs, then give another 1/2 turn each bolt. I was sweating buckets waiting for them to strip, but they held! No idea what the final torque was but I was scared.
Art Pearse

This thread was discussed between 11/03/2013 and 16/03/2013

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