Special Engine Marks

Information identifying undersize crankshaft journals, oversize cylinder bores, tappets and valve stems is stamped in various locations on engine, depending on engine. Information and location is decoded as follows:

R or M  - Numbers 1, 2, 3, or 4 following R or M indicates 0.001" (0.02 mm) undersize rod or main bearing journals and which journal is undersize. Stamped on number 8 crankshaft counterweight.

RX or MX  - Indicates all rod or main bearing journals are 0.010" (0.25 mm) undersize. Stamped on number 8 crankshaft counterweight.

A  - Indicates 0.020" (0.50 mm) oversize cylinder bore. Stamped after engine identification number.

" " - Indicates 0.008" (0.20 mm) oversize tappets. Stamped on top pad at front of engine and on a flat surface at outside of each tappet bore.

X  - Indicates 0.005" (0.12 mm) oversize valve stems. Stamped on milled pad adjacent to two 0.375" (9.52 mm) tapped holes on each end of cylinder head.