Packard Forum Index » V-8 (1955-56)

FWIW, the latest shipment of Egge pistons have the steel autothermic expansion strut cast in to them.

Their fitment specification is still .0025"-.003"; considerably more than the .0005"-.0015" called for with OEM Packard pistons.

jack vines

.003" clearence wouldn't worry me in the least. I'd much rather have the .003 than the .0005 in any engine. Worse case mite shorten ring life from 100K miles to maybe 80K miles.

I'd much rather have the .003 than the .0005 in any engine

It all depends on the specific expansion characteristics of the piston in question which is why the recommendation for clearance should come from the piston manufacturer; never use the factory clearance specifications for non-factory pistons, even those that might look physically similar.

The Packard V8 OEM pistons were "Bohnalite autothermic aluminum alloy with a cast-in strut of Invar low expansion steel alloy of 36% nickel and 64% iron, which assists in keeping the piston from expanding", is all I've ever seen.

FWIW, the Bohn Aluminum and Brass Corporation was located on 2512 E. Grand Blvd., just down the road from the Packard plant. Bohn was a major piston supplier to GM and other OEMs up into the 1980s. Beyond that, I have no more info.

Probably the cost to fit pistons tight by hand contributed to Packard's demise? Each piston was measured, marked with a one or two letter code and put in box of similar sizes. Each finished cylinder bore was measured and stamped with a one or two letter code on the bottom edge of the block. The assembler had to look at the rod number, look at the block letter code and hang a matching piston.

jack vines

Jack, I believe I'd fit them at .0035"-.004", but that's just me. I had heard a couple of years ago about the steel strutted Kanter/EGGE available now, but have not tried a set. It will be interesting to hear how the ones you just bought turn out.

Even the earlier gen EGGEs will cool down eventually, even if fitted at .002"-.0025. But it takes a good 20,000 miles or so, at least the two motors I used them in took that long. Probably would cool down a lot quicker if fitted at .0035"-.004".

Hope you'll keep us posted on how yours turn out.

Anyone with a variety of oem,nos, nors or repop pistons might try an oven test at 200 to 300 degrees F TO measure expansion.

Could even use scrap or used pistons for the test.