Ray (and all the listers):
As I understand it so far, shifting the bores is to maximize the wall
thickness. If I were to do this, instead of the thinnest spot being
.145", I could probably keep it at .155" or so. But it may all be a
moot point. When I ordered the pistons from DBE and asked about minimum
wall thicknesses, the parts guy on the phone asked Dave Bean himself,
who said that .075" - .080" is adequate. So, even if I don't shift the
bores, I am still almost double that in the worst spots, and nearly
triple it in the best places.
But here is a question for you. If you think of the any shifting along
the line of the crank as fore/aft, and the other directions as side to
side, it would make sense that shifting a bore side to side .015" would
not affect anything with regard to the crank/rod relationship, since any
shifting is in the direction of normal movement of the parts anyway,
correct? But if you shift the bore fore/aft .015", there needs to be
some play somewhere to absorb the shift. The crank/con rod tolerances
are much to tight for that, I think. But isn't there a fair amount of
room for the piston to float fore/aft on the wrist pin? The engine
builder who did the sonic test said that it was no problem, and showed
me an example of some big bore American piston for his sprint car.
Indeed, there was tons of slop. But what about our delicate little
Lotus flowers? Does the same apply?
To answer your question about the overbore to .060", the block was
already bored to .030" by the PO. The wear and corrosion is more than
can be corrected with .040". So, I am not doing it for added
displacement, but to avoid sleeving. But I won't mind the extra CC's,
as long as I am doing it ;-) Let's hear it for a 1615cc Twink!
One last question for your Carroll Smith engineering books. Does he
provide a definition of tufftriding? And even more importantly, is
there a method for determining if it has been done to a part (crank,
specifically)? And what is the wisdom if the crank journals need to be
reground rather than just polished? Rod Bean and Ken Claiborne both
provided definitions, but I think all of us would be interested in a
"textbook" description.
That's all for now.
Thanks,
Dave
Seattle
|