willysmjeeps.com

Do all M38 engine blocks come with an MC xxxxx stamping
on the water pump boss? Have an engine with J3 xxxxx stamping
on the water pump boss but it appears to have the M38 front engine
mount, reinforced bell housing mount and the coolant drain in
an area further back to accommodate the larger generator.

Thanks!
Wally

Yes, all original M38 blocks are stamped MCxxxx. The J3xxxx stamped block is civilian (cj3a, I think). The front engine plate and later (10 bolt) bellhousings are interchangable and not a good indicator or origin.

The only way to positively ID any 641087 or 804380 block casting as an original M38 series engine or original M38 series factory replacement engine is the MCXXXX for a factory installed engine and the RMCXXXX for a factory replacement engine. JXXXXX or CJ2AXXXXX or 3JXXXXX or UXXXXX would be civvy L134's. A 4LRXXXXX would be a factory replacement civvy L134 engine.

Thanks for the clarification.

Wally

Keep in mind that many of these engines, when they were rebuilt, had the block decked by the machinist. This often completely removed the serial number above the water pump. Once that serial number is gone the engine looses it's original identity completely. There is no way to prove it's pedigree after that.

Wes,

What if the engine has an FA at the beginning of the number above the water pump?

Thanks