How do you decode the markings on an F Head engine?

m37brat · Post by **m37brat** » Tue Jun 30, 2015 8:10 pm

We just found a nice F Head to rebuild for our M170. There are things that make us think it me originally been a military engine. Is there any way to decode the numbers cast into the engine that would identify what the engine was built for? Based on who I bought the engine from makes it possible that it may even be from an old M170. Some of the things I read online seems to look like the serial number stamped on the block may give I hint of what vehicle the engine came from and also an approximate production date.

If anyone knows of sites I could research or thread to look at would be a great help.

Thanks

Xamon · Post by **Xamon** » Wed Jul 01, 2015 10:33 am

Post the serial and Wes can probably tell you, the prefix is the bit that tells what it was for such as MB or RMC etc.

m37brat · Post by **m37brat** » Wed Jul 01, 2015 5:00 pm

The number stamped behind the water pump is 96071

Post by **wesk** » Wed Jul 01, 2015 8:37 pm

The number is not the key. The prefix is the key. The only real evidence of what vehicle the engine left the factory in is the prefix to that number.

MD = Engine came from the factory in a M38A1 or M170.
RMD = Engine was a factory replacement engine shipped from the factory to the user.

m37brat · Post by **m37brat** » Thu Jul 02, 2015 4:42 pm

Our block does not have a prefix. Does this indicate that the engine comes from a civilian jeep? If that's the case, are there any difference in a military block and a civilian block?

Thanks for the help. Jim.

Post by **wesk** » Thu Jul 02, 2015 10:12 pm

You have a prefix. It is just not very clear. All the L134's and F134's built by Willys & Kaiser have a prefix. J, CJ, 3A, 4J, T, U are all civilian prefixes. Just like the military blocks the civvy factory new replacement engines add the "R" somewhere in the prefix.

Try visiting my photo albums: http://www.willysmjeeps.com/v2/modules. ... _album.php

especially the engine albums:
http://www.willysmjeeps.com/v2/modules. ... _album.php

http://www.willysmjeeps.com/v2/modules. ... _album.php

The bare blocks and heads were used on many applications at the same time and differed only in the bolt-on accessories like the carb, starter, generator, fuel pump. The only fool proof and precise way to determine what chassis model a Willys or Kaiser engine originally came in is the prefix on the serial number. Without that prefix you can never prove what it came in period.

Casting numbers evolved over the years starting in the early 30's. The M38 used three different castings from 1950 thru 52 and those same three castings are found on CJ2A's, CJ3A's, pickups and station wagons. Anyone can dress up a MCXXXXX engine with civilian carb, starter, generator, fuel pump and anyone can dress up a JXXXXXX engine with a military carb, starter, generator and fuel pump.

m37brat · Post by **m37brat** » Fri Jul 03, 2015 3:11 pm

Thanks Wes. You have to be the most knowledgeable jeep guy in the country. So far we can't see any prefix so we will have to wait until we get the head off. So until now we just move forward and get busy building a nice military engine. I'm sure as we proceed we will need more help.

Jim

Post by **wesk** » Fri Jul 03, 2015 8:50 pm

Get some fine steel/iron ground dust and using a magnet see if you can dust the serial prefix area and then magnetize that area of the block.