M38 engine

shotgun · Post by **shotgun** » Fri Jul 24, 2009 2:00 pm

After many years I finally own a M38. I'm new to jeep but a old motor head. Looking over the jeep I think I know what I have but would like some advice. Things I know, I have a m38 body and frame painted red.
I have removed the old paint and found the US ARMY 20899314 on the hood. No rust to speak of but the back floor has been cut, I was told that the fire department owned the jeep and haul water for brush fires, who knows.
What i'm not sure of is the engine. I think I have a m38 block with a cj head and wo carb. The motor, head, breather are painted chevy orange.
The head has no bypass hose on the front. The engine is running fine so I not going to remove the headbolts to see the head cast number. The only number top of the water pump is 010 nothing else, they are to one side. The pulleys are double and the cast number 641087. I have a title and number MC20352.
I see alot of orange engines in M38 on the web. Were they painted orange after military rebuild?
The engine runs, low and four wheel work. First I'm going to weld up all the Bubba holes, remove the body, balast the frame and paint.
Paint the engine and drive train back to the Army color. Blast the body and paint. Put her all back and deal with the head later. That my plan any input would be appreciated.

TomM · Post by **TomM** » Fri Jul 24, 2009 6:05 pm

Congrats on finding an M38 and it sounds like you are on your way to a good machine.
Your block is correct for your early M38 but also the 641087 was used in other Willys. The only way to truelyknow if that block was in the jeep is to see a serial number on the machine flat above the water pump stating "MCxxxxx"
Here is some information on M38 engines:
http://ww2jeeps.com/htm/willysmc.htm
The original M38 would have a head with the bypass hose to the water pump as you mention. It is not uncommon for these vehicles to go through a rebuild during their life or complete engine change for a civilian equipped replacement.
The red paint would not be from the factory but there was no standardized rebuild color as far as I know. It was up to the rebuilder to choose his decor. My rebuilt engine was also red when I got it but I also have a blue block.
You can always pick away at details as you get the jeep back into the condition you want. If you find an MC head and water pump it will give motivation to renew the head gasket and have a look inside the engine but since its running there certainly is no rush.
You can get replacement sheetmetal for your floor where its cut so no problem there either.
Enjoy that project.
Tom

Post by **wesk** » Fri Jul 24, 2009 6:11 pm

I have a title and number MC20352.

Do you have a serial plate on the dash with 20352 on it? Do you have a patent plate on the front end of the right rear wheel house with MC 20352 on it? What is the engine serial number on the small flat above the water pump?

Post some photos of the jeep.

shotgun · Post by **shotgun** » Fri Jul 24, 2009 6:29 pm

There is no plate behine thew seat, I can see where the four screws were. The block has 3 numbers 030 thats all, they are all to one side.
I wire brushed the block ,ink no more numbers. I'm going with correct block, wrong head and carb and start welding holes. I do not get in any hurry on my fun projects. Thanks for any help.

Post by **wesk** » Fri Jul 24, 2009 6:37 pm

Do you have a serial plate on the dash with 20352 on it?

The engine serial can often be better viewed by sprinkling some fine steel or iron powder on the flat and then magnetizing the flat. Where the metal was disturbed by the stamp you will see the outline in the iron dust.

shotgun · Post by **shotgun** » Sat Aug 08, 2009 7:14 am

Tom M. Looking at the picture of the early m38 block it looks like the mc number is not on the flat spot top of the water pump. Are the number in other places?

TomM · Post by **TomM** » Sat Aug 08, 2009 8:21 am

To the best of my knowledge, the factory serial number will always be on flat behind the waterpump for whether CJ or M38.
Early WWII ('42,'43) had another flat on the right side, front, top hidden behind the oil filter for serial numbers.

It is not uncommon for a block to be decked during a rebuild thereby skimming off the serial numbers. Again, per Wes's note, sometimes magnetic dust or a diluted acid will allow you to see a faint outline of the original stamping.

Tom

Post by **wesk** » Sat Aug 08, 2009 9:24 pm

Shotgun,
I have done a ton of research on the M38 and it's engine. The WWII jeeps and the early CJ2A's had used the small machined oval on the upper right forward side of the block behind the oil filter bracket but that was on the WWII 638632 and earlier Willys block castings. The M38 used the 641087 casting from unit #1 thru May 1952. This casting had two primary configurations both of which placed the serial numbers on the flat above the water pump. The 804380 casting that showed up in May 1952 did the same.

The web site Tom referenced above is incorrect. The 641087 block was used thru May 52. It was changed from the early 4 bolt rear flange, 4 freeze plug block at engine Serial MC74419 and Chassis serial MC53262 to a 10 bolt rear flange, 2 freeze plug block. This later 641087 casting continued in use until it's casting number was changed in May 1952.

This is the only serial number location for all three M38 production engine blocks.

This early 641087 casting has both serial blocks shown just to make sure you knew that some had the side serial box but again only the front one had a serial stamped on it for the M38's.

This is the later type 641087 casting with the reinforced rear flange that now has 10 bolt holes (two 3/8" and three 5/16" each side) and only two freeze plugs on the side.

Here's the final M38 block casting 804380.

I have several hundred photos available for anyone wanting to research M38/M38A1/M170/M606/CJV35 data for free access on my photo web site:
http://wsknettl.mypicgallery.com/

JeepdaddyRC · Post by **JeepdaddyRC** » Thu Jan 16, 2020 3:21 pm

If it's not uncommon for a block to be decked during a rebuild thereby skimming off the serial numbers, what would a good engine rebuilder/restorer due to preserve this valuable information?

mbullism · Post by **mbullism** » Fri Jan 17, 2020 8:48 am

JeepdaddyRC wrote:If it's not uncommon for a block to be decked during a rebuild thereby skimming off the serial numbers, what would a good engine rebuilder/restorer due to preserve this valuable information?

It's also not uncommon for a 60-70yo engine to have been rebuilt multiple times by the time it comes your way, and the first time 50 years ago the number may not have been of any interest. Occasionally you'll find them restamped, but then you usually have no idea when it was done or if it's correct anyway

Post by **wesk** » Fri Jan 17, 2020 1:19 pm

Many engine shops do take the time to re-stamp the serial in a place more likely to survive longer. If you are from a state that used engine serial numbers for titles up thru the late 60's then those engine shops were quite aware of the need to preserve the number. Other states that used chassis serials the shops were usually less diligent.