924Board.org

[MikeJinCO]

I am thinking about going up to a 88mm bore piston on my rebuild to both increase displacement and lower any potential valve shrouding if I should go to 44mm intake valves. My research shows that the standard head gasket has a bore of 88mm so that 87mm would be about the largest overbore one would want with a standard gasket.

What is the availability of oversize head gaskets?
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Mike


'67 MG Midget Dp
'71 Ocelot Dsr Kawasaki 1000(under rebuild)

[ideola]

I can get Cometic MLS or copper gaskets in any bore size you want.
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erstwhile owner of just about every 924 variant ever made

[Rasta Monsta]

Boom.
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Toofah King Bad

• WeiBe (1987 924S 2.5t) - 931 S3

[MikeJinCO]

Thanks for the info, I think I stay at 87mm so that I can use a standard head gasket.
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Mike


'67 MG Midget Dp
'71 Ocelot Dsr Kawasaki 1000(under rebuild)

[WEASEL149]

Both Goetze and Reinz OEM gaskets that I have are 88.5mm bore.

You'll be ok up to 87.5mm with standard gaskets.
The problem with boring out to 88mm with standard gaskets is the fact that when the standard gasket crushes the gasket bores can crush slightly oval. This can push the fire ring into the combustion area and cause premature failure.

Using a Cometic, copper or bi-metal gasket and making sure the block and head surfaces are prepared properly, you could bore out much further than 88mm and the gasket will seal fine. There's a huge amount of meat in these blocks and there will still be plenty of material left between bores.

Boring out to 90mm with 44mm inlet valves would have been my preferred route but I found 87.5mm old stock forged pistons for a good price.
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1979 UK 932

[leadfoot]

you can use stock gasket with 88mm bore no problems...
I keep tabs on the guy who bought my original car and it's still going strong after 5 years since the rebuild,
Stu
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1981 ROW 924 Turbo -
carbon fiber GT mish mash
LS1 conversion in progress...