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MG MGB GT V8 Factory Originals Technical - CYLINDER HEAD TORQUE

I am installing felpro composit head gaskets in my 3.9. I need the torque values for the head bolts. Are they torqued normally or is it better to torque to yield?
Jim

Jim The cylinder head torque is 65-70 ft-lb for the center and inner row which is all the newer heads have. The 3.5 and early 3.9 have an outer row with 4 bolts. They are torqued to 25-40 although RPI and others suggest 20-25 ft lb. These figures are from the 92 Range Rover manual
Keith

Jim, what I have done with these motors 3500, 3900, 4200, 4900 with rover or Buick heads is tork the heads to 55lbs on ALL the bolts! I run from 9 to 1 comp. to 12 to 1 with the 4.9 & I will ONLY use the steel shim gasket, for it will give you a 1/2 a point more comp. After it runs for 30 min I let it cool over night & re tork the next day then again after 2,000 miles & then after every 10,000 miles or once every year. I have over 500,000 miles on MY M.G.B.s with the V-8 & have NEVER had a head gasket problem one, OR bwith the ones that I have built for others. I know the new rover says to tork to 95 ft.lbs. but not my motors!
Glenn Towery

There is a good deal of variance in what these motors will tolerate. Those high torque values may be fine with a brand new unused Rover engine, but otherwise you can very easily find yourself pulling the threads right out of the block. The old rule of thumb is that for threads in aluminum and a plain steel fastener there should be no less than 1-1/2 times the diameter in thread length, but after factoring in the high strength bolts and the cast rather than rolled aluminum it is easy to see that the first thing to go is not going to be the head bolts, but the threads in the block itself. If you torque to yeild then, the thing that is yeilding is the aluminum threads in the shear plane along the root of the thread. Any movement here at all will substantially compromise the system and require eventual repair.

The goal of any fastener torqueing proceedure is twofold. First to give even clamping force, and second to stretch the fastener so that the clamping force will be maintained over a long period of time. Clearly we have a slight problem in that the clamping force required to stretch the head bolts can damage the block so Glen's recommendation to use a lower figure and retorque regularly is a good one. However, if you feel you can justify slightly damaging one thread and are competent to tell by feel just exactly when the yeild point is reached, you can determine what max torque -could- be and back off from that figure, resulting in longer intervals between re-torque. Personally, I use the figures published by Chilton's for the 215, probably the lowest recommended figures, and then stay at the low end of the range.

As far as the uneven bolt pattern is concerned, That's one reason I like the Olds engine for forced induction systems as it has the 6 bolt pattern and equal clamping. On the 5 bolt pattern the safest thing to do would be to leave out the lower row of bolts because they cause uneven clamping pressure (Dan Lagrou will tell you this has been proven by testing) but few will do this. The second best alternative is to torque these bolts lightly, however I don't think the factory made any distinction so use your own best judgement.

Jim
Jim Blackwood

The factory V8 manual says 68 for all three rows. As I'm shortly to put my heads back on I would be very interested to see confirmation of the lower figure for the third row.
Paul Hunt

Paul,

RPI recommends 20-25 ft/lbs on the lower row.

http://www.rpiv8.com/engine-4.htm#gaskets
Carl Floyd

Can anyone supply the part numbers for these and/or similar gasket sets. I'm running a 3.9 litre with Buick heads.

Thanks

rick
rick ingram

Paul,

I'm pretty sure Dan LaGrou uses the lower figures for the third row, You might want to ask him what references he has for it.

Jim
Jim Blackwood

Clive Wheatley always uses the factory figures for all three rows, Roger Parker says that the third row was deleted when the composite gasket was introduced but now torques it to the lower figure even when using a metal gasket (with Wellseal).
Paul Hunt

When I torqued my heads (with composite gaskets) I had not heard of this recommendation for lower torque on the third row.

Should I leave well alone or retorque this row to the lower setting??
Ian G Buckley

I'd leave it alone. If you loosen it now it could allow a leak.
Jim Blackwood

This thread was discussed between 08/03/2003 and 15/03/2003

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