Packard Forum Index » V-8 (1955-56)

Dave, I called and left a message for Dan that I would buy a set.

JV wrote: "Not even a remote possibility of using a diesel piston interchange. A diesel piston of the same bore diameter has a piston pin 50% larger in diameter and the piston weighs 2X as much."

Ultimately true, yes. But if a close piston can be found that just so happens to have a larger than Packard pin then what about eliminating the pin bushing in the rod and simply pressing the larger pin of the donor piston into the Packard rod. This is way most modern engines are assembled. The pin floats in the piston and is pressed into the rod. SBC, F 2.0 4cyl, among others.

We've been over this many times. Let's try to explain it one more time. Diesel pistons, rods and crankshafts have to be built hell-for-stout to withstand the 20-1 compression:

1. The International Harvester truck diesels are the closest in the book, offered in a 4.00" and 4.110" bore sizes. These pistons w/pins are TWICEas heavy as a Packard piston w/pin. This doubling of the reciprocating weight would make it practically impossible to balance the crankshaft. If it could be balanced by milling out the counterweights and filling them with Mallory metal, the combined reciprocating/rotating weight would then overstress the crankpins and break the light Packard crankshaft.
2. The IH piston pins are 1.1101" in diameter. This is .1297" larger than the Packard pin. The machine work cost to bore and hone eight rods to size is considerable. The rod small end could possibly be bored out to that oversize, but strength would be unknown.
3. Diesels don't turn fast, so the inertia of heavy pistons isn't a problem at 2250 RPMS. Inertia goes up by the square of the RPM, so the doubled weight of the diesel piston would literally pull the spindly Packard rod apart at anything above 3,500 RPMs.

Bottom line, a diesel would be the worst possible place to look for a piston interchange.

thnx, jack vines

Thanks Jack for your patience in going over this yet again. I guess some folks just keep thinking that some simple solution has been overlooked. I hope those interested in the possibility of autothermic strut OEM-type pistons have contacted Dan. I know of several who have, myself included, let's hope it's enough.

Yes. I'd like to thank Jack for being patient with 'some folks' too. We're all in this together for the long haul. :o

I agree with Jack on this. And besides, has anyone ever seen a diesel piston? I don't think you'd want to use one, unless you want an ultra-low compression ratio.

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hey jack and eric, i also work in an automotive machine shop. just fyi there is a pontiac aftermarket rod now available that is the same size on the big end as a pack, a little long, so it can be use with a shorter deck piston, and a lot stronger! I also agree with the custom piston idea. but then again i'm building a 374 with an isky cam oversized valves, headers,mallory ignition system, higer ratio adjustable rockers and dual afb's. humm guess i want my Packard to PREFORME!!!!!

p.s. yes it's fully balanced!

Green Dragon.

Are u using the Pontiac rods in your 374 Packard V8???