I knew that bearings were thinner at the parting line on each side to allow for the hammering they get....so they won't close up on the journal and wipe the oil off. What I did not know is that they come in different levels of eccentricity. In other words, if you take an old bearing shell and place it like a "U" on a hard surface and beat on the inside of the shell with a ball-pien hammer, it'll curl up like a potato chip. I think I remember it was Smokey Yunick who discovered this and had the bearing manufacturers begin making bearings egg-shaped with the wider part of the shells at the parting line to prevent their curling up or "pinching" and wiping the lube off the journal.
Here's some info from Clevite 77 that helps to explain the "L" and "M" stampings on your bearings.....
"Connecting rods are subjected to high inertia loads at the top of the exhaust stroke when the weight of the piston, rings, wrist pin and top end of the rod are all pulling on the rod cap. This loading tries to stretch the rod and pulls the big end out of round causing it to close in across the parting line. In this case, bearing wall eccentricity provides extra clearance to let the rod flex without having the bearings contact the shaft. Besides low, medium and high eccentricity, Clevite 77® High Performance Bearings are offered with numerous additional features to make them compatible with related parts and suitable for the loads and speeds of competition engines."
The "L" stamp is for "Low eccentricity", while the "M" stamp is for Medium eccentricity. If I'm understanding the above paragraph correctly, I'd install the M bearing shell in the rod cap and the L bearing shell in the main part of the rod.
Last edited by techinspector1; 09-12-2007 at 08:40 PM.