The SM420 was available from 1947-1967.

All 216/235/261 engines had internal lubrication to the crankshaft main bearings.

The 216 engines and early 235 engines had babbetted rod bearings that were lubricated by directed oil spray and dippers (splash-oil was a lubrication description for earlier engines).

The later 235 and 261 engines' insert rod bearings were internally lubricated.

The 250 engine's 7 main bearings was a significant difference between that engine and the later Stovebolt 6 engines (all 216/235/261 engines had 5 main bearings).