A - RMC68963, early 641087 casting, was a LKY Ordinance Depot rebuild 1959 (bores + .020, Mains & Rod - .010), intake is early civvy
Thanks Wes.
A few more steps for my untutored mind ....
* Would a 1552 M38 ever have been an engine transplant recipiant ...using a RMC engine (early casting 641087 / S# RMC68933) ... with the work done at LKY Ordinance Depot in 1959 ? (Historical possibility for my 52 M38)
* Can the intake (intake manifold) of that block be replaced with an original 1552 M38 intake manifold?
* If undamaged, can the camshaft and driveshaft of a CJ2A be used in rebuilding this RMC engine?
Options on M38 engine replacement very welcome.
Thanks, Don _________________ Don Alvarez
Retired HS Teacher
Central Florida
M38 Project
Joined: Dec 10, 2017 Posts: 336 Location: Southern Maryland
Posted: Thu Dec 03, 2020 12:19 pm Post subject:
The correct timing gear with crank is laying on the cart next to the block. I didn't take a close up pictures of it because Don was asking for a bare block only...he wasn't interested in the engine internals which are all in the milk crate. I bolted the manifolds on the RMC block just to get them off the floor.
The straight cut gear crank is an extra, I have no history on it.
The Industrial block (804380-W-13-D-25 CU-CR with 13 T on the drivers side and no serial number) still has it's crank with a double groove pully, but I don't know if it's a gear or chain drive. I tried to rotate the crank to see which way the distributor turns, but the distributor just spins free...the engine does make compression. I bolted the water pump on just to get it off the floor, so don't factor that into anything. The front motor mount plate is the Military type with one tab facing the front and one to the rear.
Mike B _________________ Mike B
1953 M38A1 Brush Truck
1952 M38
1951 M100 Trailer
Joined: Oct 02, 2014 Posts: 1905 Location: South Carolina, Dorchester County
Posted: Thu Dec 03, 2020 1:00 pm Post subject:
Hey Don,
You think the water is getting muddy? You haven't seen anything yet!
Quote:
* Would a 1552 M38 ever have been an engine transplant recipiant ...using a RMC engine (early casting 641087 / S# RMC68933) ... with the work done at LKY Ordinance Depot in 1959 ? (Historical possibility for my 52 M38)
* Can the intake (intake manifold) of that block be replaced with an original 1552 M38 intake manifold?
* If undamaged, can the camshaft and driveshaft of a CJ2A be used in rebuilding this RMC engine?
Yes, a 1952 M38 could very well have been subject to an engine replacement during it's service life, at any depot including LKY. The "R" in RMC is "Replacement" (not Rebuilt). But there's no way to prove it. Any RMC serial numbered engine would be appropriate for your effort.
Yes, the intake/exhaust manifolds can be replaced with the correct M38 manifolds.
If you're after a correct M38 motor, no, the camshaft from a chain drive CJ2A motor cannot be used on a gear drive motor. Every M38 was delivered with a gear drive motor. As previously mentioned, the chain drive spins a different direction than the gear drive. Chain drive cams have a helical cut gear in the middle that spins the oil pump and distributor in the opposite direction from the gear drive camshaft.
My suggestion is that you want more than a bare block. You want the crankshaft and caps original to the block, along with the camshaft, and the connecting rods. You can live without the pistons, oil pump, etc because odds are you'll replace them with new in the rebuild process.
You can find serviceable, even NOS crankshafts (big bucks), but will take extra special machine shop work to properly fit it to the block. NOS gear drive camshafts and connecting rods seem to be fairly common. _________________ Ron D.
1951 M38 Unknown Serial Number
1951 M100 Dunbar Kapple 01169903 dod 5-51
The only good sports car that America ever made was the Jeep."
--- Enzo Ferrari
Would a 1552 M38 ever have been an engine transplant recipiant ...using a RMC engine (early casting 641087 / S# RMC68933) ... with the work done at LKY Ordinance Depot in 1959 ? (Historical possibility for my 52 M38)
Not likely. Very few M38's stayed in service long enough to get processed as a complete jeep rebuild at an army depot. WWII jeeps it was common as were the M38A1's. More likely that engine was simply shipped to the depot for O/H and then it re-entered the Army supply system. You'll never know when and by whom that RMC engine made it into your M38.
Quote:
* If undamaged, can the camshaft and driveshaft of a CJ2A be used in rebuilding this RMC engine?
Best to abandon this line of thought. Mike said if you look closely at the photo of the two engines together you can see the correct gear drive crank for the bare block.
Quote:
The Industrial block (804380-W-13-D-25 CU-CR with 13 T on the drivers side and no serial number) still has it's crank with a double groove pully, but I don't know if it's a gear or chain drive. I tried to rotate the crank to see which way the distributor turns, but the distributor just spins free...the engine does make compression. I bolted the water pump on just to get it off the floor, so don't factor that into anything. The front motor mount plate is the Military type with one tab facing the front and one to the rear.
The late 804380 casting enterred service in Jun/Jul 1952. It was used in the M38 & the CJ3A. Both these engines used a front plate with the left ear forward. It's timing gear cover appears to be a gear drive cover. It's double pulley is not M38. It's a civvy that uses the wide belt from the water pump and uses a narrow belt to drive an additional accessory like a hydraulic pump or governor. _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
Posted: Fri Dec 04, 2020 8:49 am Post subject: Engine put on back burner
Unknown variables are the bane of both science and wisdom.
With forum suggestions I found several sources for an engine in other states but obviously my knowledge base is in need of improvement. A more detailed list of desired engine attributes is in the making.
For now I will search locally (Florida), allowing inspection of the engine and maybe testing by my rebuilder before making a purchase.
Back at the barn there are plenty of things to do for now that I will add to the project report.
Don _________________ Don Alvarez
Retired HS Teacher
Central Florida
M38 Project
Posted: Wed Dec 09, 2020 11:20 am Post subject: Bottom line on engine choice ???
To check this horse is down & done .... is the following true?
The original engine block in a M38 with delivery date of Feb. 2,1952 .....
and matching body data plates stamped MC52408 ...
would have had the casting number 641087 .....
but that alone would not prove the engine actually is the original....
which would require some other unlikely form of provenance not available from military records.
If replacing a civilian engine found in jeep MC52408, the most historically appropriate block choice would have the 641087 casting number, with no other block features known that would further contribute to the authenticity of the rebuild. The other M38 engine components selected would be matched to the 641087 block to further contribute to authenticity. 🧐 _________________ Don Alvarez
Retired HS Teacher
Central Florida
M38 Project
Don, It is not that simple. I suggest you spend a little time perusing my photo albums. The link is at the bottom of all my posts. I have several thousand detailed technical photos there that usually can answer 90% of all the questions asked here.
The first thing you will see in my M38 engines sub-album is how many versions of the 641087 block exist. Take a day or two and digest the info in my album then give me a call PM Email and I'll provide detailed answers to your specific questions. _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
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