318 Main Bearing replacement difference.

[Dart Into Traffic]

I have a 1974 Dodge Dart Swinger, factory 318 car with the original 318. I took it out to freshen it up a little. I bought a set of King main bearings # MB55354SI to replace the originals. The bearings I pulled out are original. They have the manufacturing date of "5 74" stamped on the backside. The factory bearings for the # 1 (front) main bearing is a grooved upper half and a smooth bottom (cap) half. The replacement set I bought has 3 grooved bottom (cap) bearings, Rear #5, Thrust # 3, and a third which I'm sure is designed for placement in the # 1 cap.

I have already tried doing research. A lot. I tried to get an answer out of King bearings themselves twice. They just keep sending me a picture of a schematic showing the location of where each should be installed. The won't answer my question as to WHY the front lower is grooved when the factory original is not. They will not answer me if I ask them if it is ok to run it even though the factory setup was a smooth # 1 lower (cap) bearing. So I seek the advice of the professionals on this board who may have experienced the same thing when they took apart an unmolested from the factory 318.

Thanks in advance for any info
~Brian

 

[toolmanmike]

The grooves are for oiling the upper engine as the crank spins. The more area around the bearing, the more oil get's to the cam and heads.

 

[Newbomb Turk]

The grooves are for oiling the upper engine as the crank spins. The more area around the bearing, the more oil get's to the cam and heads.

Not exactly. That groove in the bearing sends oil to the rods full time. A half groove bearing sends oil to the rods only half the time.

It has nothing to do with how much oil gets to the heads.

Run the bearings. You’ll be fine.

 

[toolmanmike]

Not exactly. That groove in the bearing sends oil to the rods full time. A half groove bearing sends oil to the rods only half the time.

It has nothing to do with how much oil gets to the heads.

Run the bearings. You’ll be fine.

From a factory service manual.

 

[67Dart273]

There IS argument as to a trade off, but You'll never see it in a mild 318. There is argument that fully grooved are weaker in a high performance situation---less bearing surface area. Remember, when it fires, it is stressing the CAP

 

[GTX JOHN]

We run fully grooved bearings in everything AND
WE run them extremely Hard! Over 8000+ in our
Superstockers when required.

 

[Newbomb Turk]

From a factory service manual.

View attachment 1716177956

View attachment 1716177957

I fully understand the drawing. But zero oil flows to the heads unless and until the holes in the cam line up with the holes in the block. Then you get oil to the heads.

Even though a full groove bearing allows oil to the rods all the time (because the hole in the crank going to the rods is always in the groove) it doesn’t change the flow going to the heads. Unless you groove the 2 and 4 cam bearings or bring in external oil.

 

[toolmanmike]

I fully understand the drawing. But zero oil flows to the heads unless and until the holes in the cam line up with the holes in the block. Then you get oil to the heads.

Even though a full groove bearing allows oil to the rods all the time (because the hole in the crank going to the rods is always in the groove) it doesn’t change the flow going to the heads. Unless you groove the 2 and 4 cam bearings or bring in external oil.

That's why I said "cam and heads". As far as the Op of this thread, run the bearings you bought.

 

[Dart Into Traffic]

Not exactly. That groove in the bearing sends oil to the rods full time. A half groove bearing sends oil to the rods only half the time.

It has nothing to do with how much oil gets to the heads.

Run the bearings. You’ll be fine.

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.

 

[MopaR&D]

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.