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MG Midget and Sprite Technical - re-torque cylinderhead hot or cold?

I have a cast iron head with arp studs and oem head gasket. any input with a breif explanation why you would torque hot or cold would be great.
thanks mates.
Shannon
Shannon moore skm

Cold. The torque figures are calculated based on the stretch of the bolt a room temperatures.
Trevor Jessie

Or with the right gasket you don't.......
Onno K

Shannon-
Send me an email ask for "Boltbabble".

Trevor - What's "room temperature"? What's "hot" or "cold" or "warm'? Why do you think the supposed expansion coefficients of the head and bolts are the only factors?

Onno - And then sooner or later you replace it. I don't on mine, but I do on a lot of other people's installations.

FRM
FR Millmore

FRM

I am now 2 years on since fitting my most recent HG.
No retorque no problems.
And it is on a 1380 that gets used hard.
Onno K

LOL. 'ere we go again. There was a quite lengthy discussion late last year.

See the archives, "Oil in coolant; recent valve job"
Last post, 18 August 2011. FR gives a great long explanation there of torquing and re-torquing.

Anyway, the upshot was, 6 of 1 for, and half dozen against, if I remember correctly.

Wasn't a sort of conclusion, that because of newer head gasket technology, with some head gaskets, re-torquing isn't needed anymore -- supposedly --? And with some gaskets, you even use a sealant?

But for the Payen black, you torque cold after hot as normal.

I'll stick to a standard head gasket and re-torque cold after hot, as I've always done, as it's served me well for 35 plus years.

Some say re-torquing after x number of K miles, is also a good idea. And, as it happens, since I noticed a slight water leak from my head a few days ago, that might just have been a good idea. Too late now though, so I'll be doing mine soon too. :( Although, as it's not affecting temp or running, and there's no water/oil mixing going on, I'm going for a re-torque first to see if it solves the problem. Not too bad though, 12 years at least since the head was bolted on.



Lawrence Slater

I'd say it doesn't matter, because the expansion coefficients of the head / block and studs are all the same (iron) and their temperatures will be more or less equal.
Art Pearse

Thanks guys for your comments. I am currently running a payen black gasket. I decieded to re-torque the head cold and notice that every stud nut turned about 1/8 of a turn more. also reset the valve clearances being that a .012 feeler guage was a no go. lookes like after re-torquing the head i was about .001 off on my valve clearances. thanks again guys.
Shannon
Shannon moore skm

If you don't re torque, you're very likely to have leaks. Fit the gasket, torque up and run the engine up to temperature, when you torque again and you'll find the nuts have become quite loose. This way, it'll seal correctly.
Robin Cohen

"Fit the gasket, torque up and run the engine up to temperature, when you torque again --- "

Hi Robin. Are you saying you torque cold, then again when it's hot? Don't you allow it to go cold again before re-torquing?
Lawrence Slater

I thought all good engineers would know that room temperature = 22C (72F). You'll find that Rabone Chesterman rules are calibrated at 22C. Although I don't think any of our garages will be temperature controlled.
P Ottewell

The thermal coefficient of expansion is NOT the same. The heads and block are CI, the studs are steel.

Grey Cast Iron = 10.8 x10^-6 m/m K

Steel = 13 x 10^-6 m/m K

Since the temperature matters, torque cold.
However, the head gasket matters too. The black Payen has been a godsend to those of us who experienced frustrating series of failures before, with the grey ones we used to get from the suppliers, back in the early '90s.

Norm
Norm Kerr

Norm, it's insignificant is what I meant.
The diff is 2.2x10-6 x say 80 deg C x say 2.5" = .00044"
This is about one hundredth of a turn of the head nut!
But if you are concerned, then it should be bolted hot as the studs would be longer when hot, than the head.
Art Pearse

You are correct, the amount a bolt actually stretches when it is torqued. It is a very small amount.

Norm
Norm Kerr

Lawrence

I had my first payen gasket leak as I torqued it cold, ran the car and never touched the bolts again. When I took the head off because of oil in the coolant, the bolts very loose enough to undo easily with a spanner! So, torqued it up cold then up to temperature, I actually ran the car through several cycles, ie used it for a few days then re-torqued when it was hot, around half a turn for each nut to bring it back to torque and it's been fine since. Torquing hot like this is no danger, as long as you follow the sequence correctly, you're not going to over stretch the studs at the relatively low torque figures that we are talking about.
Robin Cohen

Hi Robin, well that's confusing then, but if it works on yours, that's proof in the pudding so to speak.

Does anyone know what Payen actually say? Hot or cold torque?
Lawrence Slater

Used the same method as Robin many times on various engines and never had an issue. The only time I did have a HG blow was because I forgot to retorque this was when I was much younger and more stupid !!
Ed
Ed H

The reason for retorquing is head gasket compression. On some engines (eg VW Jetta) they use very long bolts and really stretch them - 50 ft lb then a half turn more. And no more torquing. Of course with OHC you dont need to adjust the valves as the HG compresses.
Art Pearse

"The reason for retorquing is head gasket compression."

But if you go on torquing, don't you risk over compressing the gasket?
Lawrence Slater

That is correct Lawrence, which is why you don't over-torque, when you re-torque, instead you loosen the nut slightly and then re-tighten it to the original torque value.

If you go above that value you risk over-compressing the gasket, ruining it.


Norm
Norm Kerr

When the cars were new, was there a requirement to take them back at 1000 miles to have the head re-torqued?
P Ottewell

Good question that Pete, and as far as I know, none of the cars from this era had that requirement.
Lawrence Slater

It does not seem to be in any published info I've found, however:
The guy I worked for c1965-70 had been the service manager for the Pittsburgh BMC dealer, and was a favourite of the traveling BMC tech bus crew - they always scheduled service on the bus for his shop. The head Tech man said that heads were to be retorqued on pre delivery and first service, without fail or exception, and the dealers were paid to do so. After he quit the dealer and started his own shop, we made a great living replacing leaking head gaskets on new cars where the paint on the head nuts was unmarked, indicating that this had not been done. The typical failure was in the 3-5000 mile range. After the introduction of the fibre composite gaskets, the failure range expanded and went up, typically 5-10,000 miles, but it still happened. This is in accord with what the old time mechanics told me as a kid, and is my procedure on all heads, including when I am replacing "No retorque" gaskets that have blown. Includes diesels, motorcycles, American V8s, lawnmowers, all sorts of British cars, and I lately saved a couple of my Mazdas which started leaking in the 140,000 mile range - without replacing the gaskets. Further, I have measured the amount of nut movement on many of these after repeated retorques, and they DO move,even after 15 or 20 retorques over years, albeit less as time goes by.

I have retorqued as I've often stated here since about 1960, and we/I have NEVER had a gasket failure. That is thousands of gaskets over more than 50 years, some on engines that have been in my possesion since I put them together over 35 years ago, undisturbed since.
You are entitled to your opinions, I stand by my experience.

FRM
FR Millmore

Just a question FRM and well answered. Nice of you to allow us our opinions though.
P Ottewell

I usually check the head stud torques while the rocker cover is off for valve lash adjustment, about every 10,000km. Two satisfying minutes with a torque wrench is a nice break from all that farting around with feeler gauges and tiny spanners.

I learned my lesson with the diesel van- it's amazing what 30psi of boost will do to a gasket when the head bolts get loose!
Growler

"But if you go on torquing, don't you risk over compressing the gasket?"

Not just the gasket at risk if you over-torque. the studs themselves are fairly close to their limit, so there's the risk of breaking one. Or, in the case of the B series, cracking the blockbetween the pushrod holes. Or even pulling the stud out of the block. I've seen people do all these.
Paul Walbran

So it would appear that good advice is frequent retorquing, hot or cold and don't over do the torque setting.
Art Pearse

Why was "warm" not an option? ;)

FWIW, I always retorque ... and I have had a head gasket failure, but I do not think it was caused by decision to retorque when cold.
Trevor Jessie

Well it's as clear as mud now then. :)

Lawrence Slater

This thread was discussed between 03/11/2012 and 07/11/2012

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