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MG MGB GT V8 Factory Originals Technical - piston clearance

Hi all, can anyone give me the min. piston to deck clearance on a 3.9 rover, with std. pistons. Would like to square up top of deck, wondering how much I could remove.
Paul

All you should take off the top of the block is .040. If you take more off you will have trouble getting the manifold bolts to line up & then you run into lifter push rod length. .)40 will raise the C.R. 3/4 of a point. Use the steel shim head gasket the other gaskets are twice as thick & this lowers the comp. raito. MAKE SURE the pictons sits below the deck.010 with the steel gasket, or the piston & head will hit.
Glenn Towery

Thanks Glen, just to clarify, if I have a Zero deck and I use .018 a steel shim head gasket I will be OK ?

or I need to have .010 below deck in addition which would give me .028 from top of outer edge of piston to bottom of head.

Thanks Paul
P Harrington

Im not a fan of the tin gaskets. Mine failed on my 4.0L GT and the result was I needed a new block. I thought the exhaust gasket was blowing but it turned out to be the head gasket. The hot gasses burnt away material from behind the liner with damage also to the head. Ended up costing me £1000.
My compression ratio is now 10.8:1 on a 4.6. My opinion is the tin gaskets arent up to it.
If you raise the compression ratio by skimming the block or heads its best to have the inlet manifold skimmed as well. I needed 30 thou off each face for it all to line up.

Mark
Mark

Paul, yes the piston has to be .010 BELOW the deck with the steel head gasket or the piston will hit! We have used the steel gasket with all the motors we rebuilt for 23 years & with my 4.9 with buick 300 heads I have 220 lbs comp. & have NEVER had a problem with any of the motors. I tork the buick,early rover 3500 heads to 55lbs The newer 3.9,40,42,46 to 65 lbs, NOT 95lbs that rover says to use. I retork the heads after 30 min. of running & after 500 miles & every 10.k & yes the motoe retork is done cold. Mark, were your heads ever retorked? Did you do 95 lbs of tork that rover said to use to start with?
Glenn

Glen,

Do you coat the steel gaskets with anything prior to installation? Do you
torque the Buick 300 heads to 55 lbs or 65 lbs on the later 4.0L/4.6L blocks?
What sort of maximum static compression do you recommend? I'm putting
together a stroker with Rover 4.0L block, Buick 300 crank and ported Buick 300
heads.

> if I have a Zero deck and I use .018 a steel shim

On my Ford 5.0L, the pistons actually are slightly above deck from the
factory. The thickness of the compressed headgasket is sufficient to keep
the pistons from contacting the head. If you're already flush, you may
need to use the thicker composite head gaskets.

Dan Jones
Dan Jones

This thread was discussed between 20/03/2006 and 23/03/2006

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