Center main bearing

Dick Deegan

Dick Deegan

Well-known member
Hello Everyone;

I am doing some work on my engine which is relatively fresh with about 3,000 miles on it. I started a thread a couple of days ago about planing or not planing a head. While setting and redoing valves and having the valve cover off, I decided to check the main and connecting rod bearings and adjust if necessary.

I removed the center main first and found that the bearing looked OK and the crank journal looks OK. However, the bearing cap has little or no oil groove. The groove is apparent at one end of the cap and just fades into nothing at the other end.

Is this normal? I thought that an oil groove was standard procedure.

Can someone post a picture of a cap with a proper oil groove if this is necessary. If an oil groove is required, how do I get one in? Also I believe that the orientation of the groove dtermines the direction front to back of the cap. Am I correct?

Dick
 
A groove was present from the factory, but is not necessary. If it's not there, and everything looks good, button it back up and drive it!
 
The caps sometimes don't have a groove but if it is there and worn that's another story. When the groove is worn and vaguely visible it means the Babbitt is worn and suspect. Orientation of the caps on a well built engine is like this- on the cap you will find a triangle that points to the cam or at least that's how I bore them. The front is the same but can be distinguished from the center by the cut. The front of the front cap has no champhor but the rear doesn't. The center is champhored on both ends. The front cap has the same triangle and is most times pointed to the cam. Some caps have no marks so, this complicates things some. Best to mark the caps and remember where they go.
 
I agree with James and have seen most engines to be that way. The last engine I worked on had both sides of the front and center caps chamfered, so whomever did the babbit must have wanted all the caps they poured to fit either location.

If your center cap fits equally well either direction, then I'd probably install it so the largest part of the groove meets a given spot on the crank first as the crank turns. That way the crank rotation would tend to force the oil into an ever narrowing groove as it runs.
 
According to Ford drawings there should be a diagonal groove across all the main bearing caps from one side to the other to the parting line releif. The triangle on the cap should point toward the cam. I do not know how to attach the drawing here, but if anyone wants them email me or go to the Benson Ford Museum. It is not normal for the groove to fade away. You may have excessive wear on one side (check clearance and crank straigtness) or your rebuilder may not have had to proper tools (KR Wilson or equivelant.) The lack of proper grooving for mains and rods has become common, and the result is you can do it Henry's way or some other way. There is an article on this in the Jan-Feb 2010 Restorer. That said, I have become convinced that for anything other than a stock engine, the center main should have pressure oil. It is not hard to do. Check Piranios' website http://www.modelaparts.net/ and there was a Fordbarn thread on this around June, 2010. Google Model A center main.
 
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