Maybe the whole thing/rumor is just bollocks? Here's a message I found over at Delphi "Hinckley "Hot Rod" Bonnies" forums. It obviously had to do with how to measure stuff and calculating the compression. Maybe someone native in the English language could clarify? Judging from the last sentence we're good...

Quote:

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MESSAGE FROM DAVE FUSSNER
Guys,
I received the OEM Triumph head and base gaskets this morning. Here are my measurements of the gaskets:



OEM base gasket (90mm bore) .011" Embossed single layer steel, coated
OEM base gasket (86mm bore) .011" Same as above, same part #
OEM head gasket (90mm bore) .037" Embossed 4 layer steel, coated
OEM head gasket (86mm bore) .026" Embossed 3 layer steel, coated


Note: The multi layer head gaskets are comprised of sections of .011" and .004" steel. The .011" sections
carry the embossments and are coated, the .004" section is flat and uncoated.

The 90mm head gasket has three .011" steel sections and a .004" section. The 86mm head gasket is comprised of two .011" sections and a .004" section.

The cylinder head gasket thickness below from Eastside Performance Motorcycles is in error. This was likely measuredover the stack of sections near the edge of the gasket. Using this method, I get .046", same as he indicates, for the 90 mm gasket. This is not the correct way to measure the thickness a multi-layered gasket as the embossments will skew the measurements even though the measurement is not taken directly over them. The correct way is to measure each section (away from the embossment) and add them together, since the embossments are pushed flat when the cylinder head is torqued. Since a dial caliper or micrometer cannot (and was never intended to) apply enough force to flatten the gasket (even at the edge) the only accurate way to determine the installed thickness is to measure each section and add them together.

Note that the 86 mm gasket is thinner than the 90 mm gasket.


These are the cylinder length measurements from Bill Gately:

Cylinder length (90 mm bore) 2.826"
Cylinder length (86 mm bore) 2.833"


Hope this helps.

DF

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and here is the previous email, sent from TJ at Eastside performance:


The dimension from base gasket to head gasket surface on the cylinder is 2.826".

I am curious as to why you wish to use a stock Triumph base gasket. If the piston is being made, then the cometic .020 gasket can be factored in ( you can sell the gasket kits that way). Since you are going from a .046" head gasket to a thinner one, keeping the base gasket thicker will keep the overall position of the head closer to it's stock position, thus keeping camshaft timing closer to its original location.
The stock gasket puts the head height in relation to the crankshaft at .013" plus 2.826" plus .046". Please make certain the engineers use a calculation that keeps at least .035 piston to head clearance and a stack of gaskets and cylinders that most closely mimics stock numbers.
Please feel free to have Dave contact me regarding this matter.


TJ Jackson

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so it sounds like the Wiseco 904cc kit is good. Mine certainly runs good.


"Wise men speak because they have something to say, fools because they have to say something."