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MG MGB GT V8 Factory Originals Technical - Cylinder Head Bolt Torque.

Hi, About to remove heads and remember seeing an article somewhere regarding not tightening side bolts to same torque as main ones when refitting heads. Something to do with causing warping and leakage?? Can anyone help? Danny.
D R Smith

Depends on your engine:

OE Factory 3.5 All at 68 ft.lbs.
OE MGRV8 3.9 Outer 60 Nm
Centre 90 Nm
Inner 90 Nm

If you are not sure which engine/ bolts you are using - best to seek advice of supplier.

Roger
RMW

If you look at the arrangement of the bolts you will see that each cylinder has one bolt at each corner, so to speak, plus another four along the bottom of the row, and as such probably completely superfluous. Originally they were tightened to the same torque as all the others, 68 lb ft, and are the last four in the sequence rather than being interspersed amongst the 'main' bolts. There have been some fears expressed that the additional torque on one side could cause warpage but whether there is anything in that I don't know. There must have been tens of thousands of engines coming out of the factory with them all tightened to the same figure, so if that caused a problem I think we would have heard about it. Some take the middle line and put them in but only torque them up to about 20 lb ft or so just to block up the holes and stop the bolts coming loose. Roger Parker advised this so that is what I did, but they were as tight as all the others when I removed them.
Paul Hunt

Excerpt:
"The heads are held on by 14 bolts. The problem lies in the bolts 11-14. When they get tightened they put an load on the upper bolts, raising the heads by a slight amount. New engines are tight but as the engine gets older the heads allow hot gasses to enter the engine,oil and water galleys. This normally occurs only when high pressures= high load is applied on the engine. Those hot gasses do all sort of mess inside"

Excerpt:
"All pre 96 V8's with the 14 bolt heads (yes that's all of them) have this problem to some degree, Its
not maybe causing a big problem (or so you think) but it is steadily killing of the detergent's in your oil".

Excerpt:
"All post 96 Rover V8 engine's no longer have the outer 4 head bolts on each bank, this is what the
engine has always needed, but took Rover 25 years to realize this. Here is what you can do...

1. Do Nothing, Well Rover got away with it for 25 years. Its a far off long term problem on new
engines and an immediate problem on all pre 96 used medium to high mileage engines, of all assumed
conditions.

2. Use conventional Tin (Shim Steel ) Gaskets "To retain compression ratio," This is actually better than it may seem, you can (we would ) refit the outer 4 offending bolts as Rover but torque them to only 20-25ft/lb. so they fill the hole but have no detrimental effect, this is generally the best option if your "Head and Block" faces are new or near perfect order

3.Fit Composite Gaskets, This is the surest way of getting the best Head gasket seal,. but unlike the above option, will lower the compression ratio by a factor of about 0.6-1. (Important to some but not
to most). Composite gaskets should also be considered when ultimate reliability is far more important then the slightly reduced reliability factor shim steel gaskets and when power is less important.


http://www.gomog.com/headgaskets.html



I personally prefer #2, but I would use good composite gaskets in place of steel shim..you must adjust your CR to compensate.
jegawatt

Another excerpt is: "A good indication of this blow-by is that the tin seal plate in the V makes a bulge as it's pushed up by the pressure."

I find this highly unlikely as the back of the crankcase, on factory V8s anyway, is open to the atmosphere. If the leakage pressure were so great as to overcome the ability of the vent to relieve it (which is what another excerpt claims causes oil leaks) I'm sure we would be well aware from other symptoms.
Paul Hunt

Thanks Paul and co. for replies to my query. Its a Vitesse high comp engine using composite gaskets and i'd been experiencing gas pressure in coolant system, not a lot but enough to make it blow off through overflow and run rough if i gave it any throttle to speak of. About to remove heads and wanted to sound people out re outer bolt torque figures. Will torque outers to about 24ft lbs and see how that goes. Regards, Danny.
D R Smith

Danny,
I've a Vitesse engine with composite gaskets, our local SD1 expert, who has done a lot of work with these engines, certainly tightened the outer bolts to a much lower torque than the rest.....that was over 20k ago.......and no problems as yet.

Mike
Michael barnfather

http://membres.lycos.fr/mgcontact/fileupload/uploads/headstuds.JPG
I have used ARP studs for holding the cylinders heads. I have used tin steel gaskets, block desk and cylinders heads re-skimmed, the engine as 500 kilometers, re-tightening the nuts, is it necessary ? What torque ?
Regards.
michel

AFAIK retightening is not performed as this destroys the threadlock seal, which should be used when initially tightening the bolts. It's not called for in the workshop manual, my V8 specialist said it wasn't necessary, and I didn't do it.
Paul Hunt

This thread was discussed between 19/10/2004 and 29/10/2004

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