Just Purchased Virgin 340 Short - What to do with Pistons

nm9stheham said
Mmmmm... you deck height is nowhere near to typical for the early high compression pistons; those stick .018" nominal out of the bores. If they are truly .070" down in the bore at TDC, then IDK what they are; they may be the later low compression 340 factory pistons, but I did not think they were down in the hole that much. The Silvolite 1267 mid-compression replacements don't sit low like that.

So is this 'in the bore by .07" ' for real or did you mean .007" or ???? Do the pistons have 2 or 4 eyebrows? What actual heads do you have?

If you were to put in newer Icon or KB or other newer pistons, you would save considerable weight. The Icon's have a light ring pack. But not sure any of that is of value to you for your use. And the crank would need re-balanced as noted.

Of course we know nothing about the condition of the present pistons, bores, rings, ring grooves. So it is a guess as to what it will do.

The measurement was 0.07" and you could visually see it into the bore, clearly, where 0.007" would look almost flush.
So yeah, I will have to tear this down to see exactly what I am working with. Virgin bore does not equate to original pistons, as I believe I have found out.

I am using 906 heads, slightly decked and cc'd at 65. They were on my 318 that I will swap shorts with, and yes, my CR went way down with these heads. The pistons do have 4 eyebrows and the top does look identical to original factory piston tops for 340 that I have seen.

I plan on using the pistons, assuming in good shape, but will probably replace rings. Can't see putting old rings back in, but I will leave that up to my machinist to determine if they are good, as I have no way of knowing.