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MG MGB GT V8 Factory Originals Technical - Head gasket question.

Hi

If your motor is rebored (say) +10 thou. do you have to get different head gaskets?

I assume not, as I've never seen "+10" head gaskets for sale. (But I thought I'd better ask.)

Thanks,

Nick
Nick Wilson

Your right Nick ! - just use the standard Gasket - the Gasket Fire Ring is usually well clear of the bore anyhow.

Pete
Pete Greenwood

Head gaskets are desinged to cater for all the available standard oversize bores. Therefore my plus 040" bore 3.5 runs perfectly with the standard fit 3.5 head gaskets. Only where you go beyond the standard range of overbores do you need to check whether the fire ring overlaps the edge of the bore and if so then a different gasket is needed, or a frequent change of the standard ones follow!!

Rog
Roger Parker

Thanks Guys,

Another question, then.

If, when I take it apart, I find the head gasket has been leaking and I decide to replace it with a composite gasket (it's a P6B motor, so reducing the CR is probably a good thing) this will move the heads up a little.

Is the purpose of the composite valley gasket to compensate for this? I.e. do you have to use a composite valley gasket with composite head gaskets?

Also, the pushrod clearance will be increased. There is a lot of chat about setting the preload, but having the rocker pedestals machined seems a bit excessive, just to use a different head gasket!

Thanks again,

Nick
Nick Wilson

Yes it will affect lifter preload, and your right that the composite Valley gasket will help towards improving the alignment of the inlet manifold. By the way I'd always go for the composite Valley Gasket rather than the origninal sort.

I think from memory that lifter pre-load should be about 30thou.. Yes, getting the pedestals machined is excessive for a regular 'budget' rebuild ! - so get a shim kit from Real Steel for £16. These kits usually contain all the necessary sizes to get things right. I think RPI do a kit too.

PG.
Pete Greenwood

Hey, it's just occured to me that your'e going the other way - ie. thicker gasket will reduce pre-load and obviously a shim kit won't help you ! (sorry). I recently used the composite gaskets on an ex SD1 3.5 and didn't even bother to check pre-load. It seemed to run fine but even being a re-build with new followers & cam did have one maybe two slightly noisey tappets - so I wouldnt do anything again without checking pre-load to see if its at least in the 'book' range (which is something like 20 to 50 thou).If your the fussy sort, it may well be better to do it properly - again Real Steel offer the necessary machining services.

PG.
Pete Greenwood

You can also get adjustable pushrods. I would try to assemble the engine and test the preload first. It turns out on my engine, after all the new parts and machine work (including composite head gaskets) I had to shim up my rockers. I had way too much preload.

Mike
Michael Hartwig

This thread was discussed between 12/12/2000 and 13/12/2000

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