318 Main Bearing replacement difference.

Dart Into Traffic said
Thanks. That's what I thought, but just can't understand why it would be changed from the factory design. I might understand if I was shipped a full set of upper and lower grooved bearings, but it seems like this is only going to provide full time oiling to the # 1 cylinder connecting rod bearing as the corresponding hole in the crankshaft only feeds the # 1 rod bearing. It just seems odd to me to have some connecting rods oiled full time, and others half time.

I also understand that the later roller cam 318's had a full groove # 1 main bearing, but I literally just pulled out a #1 lower smooth bearing that has been in that engine for 49 years, so at least in mid 1974, Chrysler gave the #1 main bearing cap (lower bearing) a smooth, non-grooved bearing. Maybe I should have just ordered Clevite to see if they supply a grooved or smooth # 1 cap bearing in their set.

From the drawing, #1 and #5 main bearings feed oil to only one rod (#1 and #8, respectively) while #2, 3, 4 main bearings each feed 2 rods (#2 through #7). Perhaps there is enough oil volume provided by half-groove main bearing for lubricating only one connecting rod.

Regardless, it's really not a big deal, it won't have any noticeable effect in any way on how your stock 318 runs. Everything about the bottom ends on these engines is beefier than it needs to be for stock applications including the oiling system; it's not a Chevy. If instead you were building up a 500-hp SBM then it might be worth taking a closer look at the oiling system.