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Owen: I can't answer your question right now. I will try and do some research over the next couple of days. Right now my main interest lays in Hudson as I am reading the history of that company at the moment.

John F. Shireman

Well, here's what I found on the aluminum vs cast iron history:

""Pistons [on the '23 model] were slotted aluminum alloy but reversion to cast iron (as in the Single Six) was made in December when aluminum was found to suffer from warpage, piston slap and wear."

Packard, A History of the Motor Car and the Company, Beverly Rae Kimes, ed., copyright 1978, Automobile Quarterly, Inc. p. 238.

I was kind of wondering about piston slap, with that 5" stroke and high piston travel speed and resulting heat, that maybe aluminum was a bit too touchy. To compensate for expansion, they would have had to undersize them a fraction, and startup may have been quite noisy, especially after some wear set in. Not in keeping with Packard standards!

Don't know when they resumed aluminum, or what changes allowed them to, but someone will be sure to get that, too.

There was a episode of Modern Marvels recently on the subject of Aluminum and its uses. It was fascinating. Aluminum was considered precious in the 1800's and before due to how expensive it was to mine and process. Aluminum is not extracted in ore form like other metals, but from a special type of clay. Alcoa biggest production site is in Australia.

Aluminum was so previous it demanded prices higher that gold and platinum. It was said that Napoleon used an solid aluminum goblet to drink from, while his guests had to use lowly solid gold ones.

But the show did get into it's uses in automotive applications.

Quote: Probably when someone figured out the autothermic piston or else casting & foundry techniques advanced to the point that the other metal could be reliably & cheaply incorporated.

1932 Eight, Super Eight and Twelve pistons were aluminum, cam-ground and controlled expansion autothermic strut design and believe the use of these dates back at least to the 1st Series Eight in 1924, perhaps much earlier.

If they were autothermic back then and still suffered from warpage, piston slap and wear, then if not casting & foundry it would almost have to be a different design or better alloy.

Any references that they suffered from piston slip or warpage? I've heard plenty of original, unrebuilt Packard engines from the mid-20s that are silent, and I've seen original OEM pistons removed that looked good enough to use again, and can't recall ever reading about piston problems. There was a service letter about 1934 suggesting that the "T" slot could be installed either way, though earlier recommendation was that it face the camshaft side of the engine.

EDIT - assuming the cite in the Kimes book about reverting to cast iron is in fact correct, I'd guess it was a very temporary measure. Packard's aluminum pistons were of a very sophisticated design, not much different than those used in all the L-8s right thru 1954.

EDIT - the pictures in the 7th series and up service letters show the aluminum 4-ring piston of the controlled expansion autothermic strut design, and states they were used from (at least) the 6th series. Perhaps Packard tried a cast or forged slug design aluminum piston, got poor results, and changed to cast iron while they quickly sourced an improved design?

The only reference I was going by was posted above and speculating as to the reasons.
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Quote: That would make sense. I imagine aluminum metallurgy was still considered in it's infancy then and maybe an early version of all aluminum pistons (which still have issues for some today despite all the advances) would have had much bigger issues then.

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Oh yes, the fabled Chevy piston slap on startup. Almost standard equipment.