Marlin Engine ID Locations
232 sixes have this number stamped on a machined pad on the right side of the block near where head and block come together between #2 and #3 cylinder. #3 spark plug shows in photo below.
First generation V-8s which back then were call Rambler engines(1956-66 250/287/327) have the code stamped on a metal tag attached to the generator bracket. The bore size is cast into the left rear side of the block under the bell housing, which must be removed for positive ID.
This tag is attached to the front of the right (passenger side) valve cover . All 290 and 343 blocks should also have the engine size cast into them on each side between the freeze plugs behind the mounting plates in cars .
OVER/UNDER SIZE CODE
UP TO MID PRODUCTION 1967:
Some engines will have a second three letter code under or beside the serial number or Day Build Code. This code is used to indicate under and/or over size parts. All three letters will be present if any part was factory altered from original specifications. If .010 inch over or under would not correct the fit of the parts , they were replaced. No engine was fitted from the factory with parts that were over .010 inch above or below standard.
The code represented the bore (1st letter), main bearings (2nd letter), and rod bearings (3rd letter). In any position, an "A" indicates standard size, "B" .010 inch undersize, and "C" .010 inch oversize.
The code is located directly below the serial number or Engine Day Build Code , on the boss directly above the oil filter on 232 six cylinder , and on the valve cover tag on V8 engines.
MID 1967 AND TO THE END: C- 0.010" oversize camshaft bearing bore M- 0.010" undersize connecting main bearings P- 0.010" undersize connecting connecting rod bearings
A different letter represents each part and the modification. The letter is located on the boss directly above the oil filter on six cylinder engines, on the valve cover tag on V8 engines. One or more letters may be present: B- 0.010" oversize cylinder bore
C- 0.010" oversize camshaft bearing bore
M- 0.010" undersize connecting main bearings
P- 0.010" undersize connecting connecting rod bearings