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Serial number identification for miltary flathead with tranny

Started by militarycaddydave, November 14, 2012, 11:08:17 AM

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Can anyone offer any info on an engine/tranny combo I have in my garage.  Serial number on the block is 5G1858 with a flaming bomb stamped after that.  The engine may very well have never been used since some of the wooden plugs are still taped into place on many of the openings. It is very complete with distributor/carb/exhaust manifolds etc.  Looks like it should be cleaned up for a museum somewhere. With the spark plugs out, it looks very clean inside with no carbon visible. "Cadillac" wording is raised on the heads. I would appreciate if someone has any idea of value for this item as well as what vehicle/tank this may have been intended for.
Thank You
Dave Yamulla

Terry Wenger


To the best of my knowledge only 3 series of military Cadillac engines were produced: 1G, 3G and 4G.

1G and 3G were used in light tanks and other land vehicles. The 4G units were used in amphibious personell carriers.So you most likely have a 3G series engine rather the a "5G" The installation of 1G and 3G engines used two engines and Hydramatics in tandem.

These engines can be converted for use in Cadillac civilian cars.I did one for a '39 in 1972. I have no idea what the value is.

Terry Wenger
Terry Wenger CLC #1800
1932 355B TSD
1939 7557
1940 60S
1941 60S
1947 6267 Conv.
1949 6207X Coupe
1963 60S

Scott Anderson CLC#26068

While I'm not able to comment on the serial number, a 'flaming bomb' is the symbol for he US Army Ordnance branch.
1941 Cadillac 6267X Convertible Coupe
2014 Cadillac CTS-V Coupe

Doug Houston

The letter "G" in the serial nuber sould be, and probably is, the identification for a 1941 manufacture.
I have always uderstood that Cadillac's engine UNIT numbers carried through the military engines, made during WW II.  The letter in the engine unit number, which could really be the true serial number as it was built, began in 1937, though it should have been in 1936.....??  Each year, the unit number had the next letter to denote the model year of the engine.

Essentially, all of the hardware used on the military engine is discarded, and the heads, and everything else would be transferred to the GI block. Don't expect to remove the cooler from the Hydra-Matic on the GI engine, and go driving off in it, either. Some of those configurations HAD NO REVERSE!

There were several fittings for cooling lines, going in and out of the engine, and they need to be plugged.

Memories, oh, memories.....One Saturday on West side Detroit, where Terry, two other guys and I whacked all of the unnecessary parts off of four of those engines in the surplus store. They were the models for some landing craft.  Fun used to take some mghty funny forms.
70-DeV Conv
41-Chev 41-1167
41 Olds 41-3929


Thanks alot guys, I really appreciate your thoughts.  I double checked the Unit number/serial number on the block and it is definitely a 5G engine with the flaming bomb. Does it make sense that this army ordinance engine was produced in 1941 when the US did not really enter WWII until 1942 or late December 1941? 
Got in touch with a very nice local man who looked at it this morning and was amazed to see this in such complete, unmolested form.  He thought it may have been only test run at the most.  He particularly noted the original GM hose clamps and the price to buy a set of repros, let alone originals.  He also noted the porcelin covered manifolds and the Carter WCD carburetor (the butterfly still moves).
There is no tag on the tranny or even an oval area where the tag is normally rivited or I would be able to atleast determine the date of the tranny.
I tend to agree that this was used in tandem with another like Terry suggested.
Again, I do appreciate your giving me some help on this.


Nearly correct, Doug.

'36 was A, '37 B, '38 C, '39 D, 40 E, 41 F and 42 G. It has never been real clear to me what happened after '42. I have never seen or heard of a "H" series, for example. Up till now I guess I have assumed that they just stuck with the G series for the rest of the war. Be nice to know, though.

Like you I have seen (and have) an F series and 1G's and 3G's but a 5G is a "find". I would suggest the 5G is some sort of variation on the "G" series block, perhaps for another military purpose not associated with tanks or gun platforms.
John Tozer

'37 7513
'37 7533