Re: 392 block was 345 block

[jlandry@domain.elided (John A. Landry)]

In a brilliant stroke of genius, "Tom Harais" <tjhemh@domain.elided> blurted
out:

>He tells me the "to the nearest ten thousandth" is for gun barrels. "To the
>nearest thousandth" is for cylinder bores. He also says honing is too fine
>a work to do what John L. said. It just doesn't remove enough metal to
>allow for it's application. He says there is little to gain in going to
>such fine tolerances in automotive work.

OK... I called Norm Lewis at Performance Engine Development in Tacoma, WA
(the place I intend to have my machine work done in the future) and he
tells me this...

If a customer were to ask for a particular bore size, they could hold the
tolerance to the nearest 0.0005" or less without trouble.  But in the
typical case where a customer wants the cylinders bored to fit new pistons,
they prefer to have the full set of pistons available to them when
beginning a bore/hone job so they can mic each piston individually and
match them one by one to each bore (they are happy to mark the block and
piston as such).  However, they said Federal-Mogul Sterling pistons come
from the factory with such tight production tolerances that this is really
not necessary for rpms up to about 7000 to 8000.  He says this is why they
use Federal-Mogul pistons exclusively in all their rebuild work when a
customer doesn't specify otherwise.

As to how they actually arrive at the desired bore size, he said they
typically start out by boring out from 0.003" to 0.005" undersize.  Then
they finish hone in steps until reaching the exact desired size.  He says
they use decreasing grit size on the stones and stop between each one to
let the block completely cool and normalize in temperature so measurements
will be accurate.  The final grit brings them carefully into the final
dimension.  He says they take a lot of time and trouble to do it this way
as it produces superior accuracy and assures the engine will last much
longer.

So there you have it from just one shop in particular.

John L.
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