Main Bearing Oil Groove Opinions

[Rowdy]

I bought a rebabitted block at an auction last weekend. It was done by a local guy with a reputation of doing good work.This was one engine he did not finish before he passed away. He used the molds with the round groove as opposed to the spiral KRW oil groove cutter. Since I have the KRW cutter and could cut the groove would it be a good idea to go ahead and cut the spiral groove or am I asking for trouble in doing this? Probably not neccessary, just curious as to opinions from experienced engine builders. Thanks Rod

[Jim Brierley]

I would just use the grooves that are in it. Putting in others reduces the amount of bearing area supporting the crank.

[Rowdy]

Thanks Jim, that was most of my reasoning for not as I did not want to weaken the bearing. I do prefer the spiral groove as I feel it oils the mains better, but many engines out there ar living fine with the single groove. Rod

[Model A Man]

for some reason on both my A's. the rear mains do not have an grooves.

[PC/SR]

Have to disagree with Jim on this one. The Model A has plenty of bearing surface for its power, the Wilson grooves are narrow, and I think the additional lubrication would be worth it. However, babbitt thickness would be a consideration before any more grooving. More important is whether there are beveled reliefs at the parting lines and thrust surfaces. They are easy to file to about 1/4 inch from each bearing end, and you really need them especially if you stay with the circumferential groove. .

[Rowdy]

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The releifs look good, about 80% of the length of each bearing. Rod

[d.j. moordigian]

Since the load is on the bottom (cap), you can do the block side.
Dudley

[Kohnke Rebabbitting]

Reliefs on the part lines on a bearing are called oil wells, and that is exactly the job they are there for. Circle grooves in bearings should be used for oill pressure "ONLY". The oil well, in combination with the spiral groove is best used on the splash bearing. You would not loose bearing surface, as the added grooves DO NOT, take away from bearing surface, but add to it. The OIL, is your bearing surface, not the lack of a oil grove in that area. A bearing will NOT FAIL because it got to much oil, it fails because it was shorted of oil. "OIL MOLECULE", is always your bearing surface, not the area of bearing that the shaft is not supposed to ever touch. Herm

[James Rogers]

Originally Posted by Kohnke Rebabbitting

Reliefs on the part lines on a bearing are called oil wells, and that is exactly the job they are there for. Circle grooves in bearings should be used for oill pressure "ONLY". The oil well, in combination with the spiral groove is best used on the splash bearing. You would not loose bearing surface, as the added grooves DO NOT, take away from bearing surface, but add to it. The OIL, is your bearing surface, not the lack of a oil grove in that area. A bearing will NOT FAIL because it got to much oil, it fails because it was shorted of oil. "OIL MOLECULE", is always your bearing surface, not the area of bearing that the shaft is not supposed to ever touch. Herm

Ya know Herm, the biggest misconception about main and rod bearings is that the babbitt is the bearing surface when the oil wedge is actually what the crank rides on when running. I may be wrong but, I believe the babbitt is there to provide the clearance for the wedge in the proper thickness. The crank should never touch the babbitt when running but ride only on the wedge. Failure of the "bearing" is because of the failure of the oil wedge and lubrication. Your thoughts?

[Kohnke Rebabbitting]

Originally Posted by James Rogers

Ya know Herm, the biggest misconception about main and rod bearings is that the babbitt is the bearing surface when the oil wedge is actually what the crank rides on when running. I may be wrong but, I believe the babbitt is there to provide the clearance for the wedge in the proper thickness. The crank should never touch the babbitt when running but ride only on the wedge. Failure of the "bearing" is because of the failure of the oil wedge and lubrication. Your thoughts?

Exactly James, the other thing that is of great importance on a Model A is the clearance of the main bearings, not the rods on a Model A, as they are of the dip design. If they are drilled for pressure, then they would be as important as the mains in the sence that the clearance as it goes over the acceptable limit, will throw off, out of the bearings, double the oil, for the rods to pick up, and throw up under the pistons, to over load the rings to scrape off, and normally will start burning more oil, until the bearings are tightened, or replaced. " and yes I know all the bearings should be adjusted.' Herm.

[Jim Brierley]

Well said Herm & James!

[hazelhoff]

I know this is an old thread but nevertheless ...
Herm and James seem to agree on an oil film carrying the load of the crankshaft. I do too ! But, pour some oil on your counter and stack some bricks. Will they float ?
You need the natural oil pressure from the crankshaft turning around (hydrodynamics).
Now, why would you interrupt the oil pressure by adding an oil groove right across the pressure bulb ? In doing this you create a pressure leak !

Henk