> 1) What gasket do I buy? 83mm or 86mm? I'm assuming you go with
> the 86mm to
> match the head?
83mm gaskets are more or less unobtanium, so use the 86mm version even if
you switch back to an early head.
> The copper gasket currently on the block seems to cover about
> half the area
> of some of the passage holes, they don't line up quite right.
That's normal.
> 2) Does this combination lower the compression ratio below the
> normal 8.5:1?
Maybe a little, but IMO not enough to worry about. I ran through the
calculations quickly, assuming the old head gave 8.5:1 with 83mm pistons and
the new head gave 9:1 with 86mm pistons (as documented); the new head with
83mm pistons would give 8.45:1.
> 3)Anything else I need to be aware of that might be a problem, am
> overlooking?
The exhaust valves, guides & springs changed; if you're ordering new
components you'll need to check which ones you want. There are special
guides available that allow late exhaust valves to be fitted to early heads.
The triple springs take a pedestal under the springs, as I recall the dual
springs don't.
> "This head style was used on late TR3A & B cars that came from the factory
> with with 86mm pistons. It is recognizable by the chamfer on the
> side of the
> combustion chamber
With respect to TeriAnn, I'm not convinced the change points given are
correct. I've owned or dismantled several TR3As with engine numbers later
than 21470E, and never found a head with the chamfer in the combustion
chamber, except for one that had a late TR4/A motor. Even the TR4 I
dismantled had no chamfer. Plus no change in combustion chamber volume is
necessary to "keep compression down" ... the change from 83 mm liners to 86
mm liners is just enough to raise compression from 8.5 to 9.0. (If it was
8.500 before, it would be 9.050 afterwards.)
Randall
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