Much as I'd like to be able to, I can't add any information other than what's in the SC, except that I'm relatively certain they did not change compression ratio of the 320 engine when going from machined to cast chambers; otherwise there would certainly have been a TSB or SC about it.

As to the forged crankshaft, friend Randy Berger found one in the 374 engine he bought for parts. He ended up using it in his rebuilt engine. It did have some numbers on it, though I didn't make note of them, though the differences in the two crankshafts are obvious just by visual inspection. I also asked Randy about the last digit on the 374 head casting number; he's pretty confident it's a 6, not an 8.

There are several notations about crankshafts in the SCs as well. Those relating to the 55th series notes that cranks balanced for the 4 inch bore have a "4" stamped onto a milled surface on the end of the front counterweight, the other has a "3". Then there is a subsequent notation relating to the first that says the crankshaft with the #4 stamped may be used for either the 4 or 3-13/16 engine, but those with the #3 can only be used on the 3-13/16 engine. I've never seen similar notations concerning the 56th series crankshafts.

OK, I've got a half-dozen 374"s so I should be able to find one on which the head casting number is readable. I'll be going up to my shop where they are stored later this week.

Let's start over on the 320" heads:

1. Were the machined 320" heads a different casting number than that of the 352"? It would have been relatively easy operation to make the machined combustion chamber 8cc larger. The as-cast chamber is what it is.
2. Has anyone seen any info to indicate when the 320" change was made to as-cast, did the valve size and/or compression ratio also change? That it was necessary to change the carburetor and distributor may have been necessary due to a higher compression ratio. Why else change those components?
3. Does anyone have a set of as-cast 320" heads. It would be interesting to check the CCs to determine if they are different from the machined heads.

As to why the change from machined to as-cast combustion chambers:
1. I doubt it was for cost savings. Machining was a simple one-pass with an end mill. It was more costly to change the pattern, pour the test castings and make the checks and remove the machining operation from the line than to leave it in place.
2. My opinion is it was the easiest way to raise the compression ratio. They just made the chamber smaller by changing the pattern to add more iron.
3. The smaller chamber also slightly shrouded the valves. This is probably why the change to 2" intakes.

Now that we're getting some traction on head casting and part numbers, how about crankshafts? In theory, with three different bore diameters and piston weights, there should be three different part numbers. Then there's the Unobtanium forged crankshafts, so six part numbers. I've never seen a casting number, forging number or part number visible on any Packard V8 crankshaft. How do we know what we should have, much less what we've got?

thnx, jack vines

So they date and vol. info was DELIBERATLY ommitted

Yes, that's what I said.

Thank you all for your compliments. I'm glad that my work has been so well-received and is of use to so many. I hope visitors look a little further to see that there is also a chart for 55th Series.

Be advised that I have received copies of factory documentation from Dwight Heinmuller that will require me to submit a revison to the 56th Series charts for a couple of points on Executive (5670) equipment. Though I don't yet have a copy of the Trade Letter (#56-1001, Dealer 1, Supplement 2) regarding the change in underseat heater availability, I'll clarify the footnote.

Before I can do that, however, I have to finish cleaing up the wreck that remnants of Hurricane Ike made of my folks' yard last Sunday. While we lost power for only a few hours, many homes in the region are still without it.

More on build codes later...

The use of volume and issue numbering for this newsletter dates all the way back to 1927, when it was launched as the Packard Service Letter. While the name changed in the mid-40s to the Packard Service Counselor, volume numbering remained contiguous through 1956.

Not only was did the publishers eliminate dates and volume/issue numbers in this new edition of the reprint, but they renumbered the pages and reindexed the whole thing. That makes for a real PIA when two people are trying to communicate and one has original issues but the other has the new reprint. Yet, previous (comb-bound) editions of the reprints were as originally published by Packard. Stuff like that really makes you wonder what they were thinking.

No matter - a solution is on the way.

A couple of years ago, I wrote a comprehensive index to all the Service Counselor articles and Service Technical Bulletins, PLUS Studebaker Service Bulletin articles for the V8s, and I am now working with BigKev to take that to a whole new level and extend its functionality to earlier Series.

Please stand by by for the premiere of this new feature (hopefully within a week or so). I think you'll find help for a lot of questions that have been asked recently - not just in this thread.

Great job Brian, many thanks! On the subject of underseat heaters, I owned an early 56 Caribbean hardtop, 1009, and it had the underseat heater. Someone suggested that only the convertibles had a problem fitting the underseat heater.

"Unfortunately my Service Counselors are the compendium published by PAC, and they (thoughtlessly) omitted the dates and numbers"

The Vol and No. along with Month and year appears DIRECTLY under the SC letterhead on the 56 SC's. I don't know about the 55 Sc's.

So they date and vol. info was DELIBERATLY ommitted.

Packard53, to try and answer your initial inquiry. I'm not a V-12 expert, but much has been written about the later twelve cylinder engines and the cars they powered. The second generation (1932-1939) V-12s had a unique and interesting valve design. The camshaft and roller tappet/lifter design had the valves sitting relatively high between cylinder banks. The valves intersected the cylinders at an angle that resulted in them being more perpendicular to the cylinders rather than parallel as is typical with a valve-in-block (L-head) design. This coupled with a pent roof piston and flat cylinder head (I believe) resulted in a combustion formed formed by the piston, valves, and a relief in the block and not by a formed chamber in the cylinder head. This design provided for fully machine finished combustion chambers. As far as I know there was no forced induction with these engines. All of this is from my recall, and I may be mistaken in some parts of this description. I also believe that the Auburn V-12 had a unique, but different valve design where the valves were not horizontal with the cylinders. There are many V-12 experts on this site that can quickly correct what I have said.

Unfortunately my Service Counselors are the compendium published by PAC, and they (thoughtlessly) omitted the dates and numbers. But it specifically says its related only to the 320 5540 model engines. I've always assumed, perhaps incorrectly, that it was a manufacturing-driven economy as the machining of the dome couldn't have been an inexpensive operation. The change also corresponded to changes in spark plug specifications, distributor and vacuum advance changes, and carburetor changes, all identified in the same SC. The engine #s that it identifies the changes as occuring at are fairly early in the 55 run, so I don't think it was in anticipation of the 56 engines. I've never seen a 352 or 374 engine with what would appear to be a machined compression dome so perhaps they were cast from the get-go?

Jack, you've seen so many 56 engines, can you verify that last digit on the casting number, "6" or "8"? I've used a magnifying glass and even so, it's pretty hard to be absolutely positive.

EDIT: Adding image from SC

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Interesting and arcane info. I've never worked on 320" heads, but by my calculations, they should have 8cc smaller combustion chambers than the '55 352" heads if both have the same 8.5 compression ratio. The Hash engines with the 352" heads on the 320" short block had 7.8 C.R., so that also mathematically checks backward.

Questions:

1. What was the date of the service letter announcing the change from machined to cast combustion chambers? I had assumed the change was made to raise the compression ratio for '56. If so, why was the change made on the 320" engine which never had a published C.R. increase?
2. Did the service letter specifically state the change was only for 320"? All later 352" and 374" had cast chambers, but why would they only announce it for 320"?
3. Was the switch to 2" intakes made at the same time? The specs for all '55s I have seen in print are for the smaller valves, but has anyone ever seen a machined chamber with the larger valves or a cast chamber with the smaller valves?
4. Since '55 352"s had 8.5 C.R and the '56s had 9.55 C.R. (the '56 Hashes got the 9.55 C.R., but still only the two-barrel carburetor.) was the cast chamber phased in at model year change for 352"?

thnx, jack vines