Connecting Rod and Main Bearings
The connecting rod bearings are metal inserts that go between the crank and the connecting rod. The main bearings go between the crank and the engine block. These are made of a softer metal so that you don't wear out your crank or engine block. Additionally, a thin layer of oil lubricates the connection between the bearings and the crank. The crank, essentially, floats on a thin layer of oil between the crank and the bearings. This thin layer is gap of approximately .001 to .0015 on our engine, when it is set correctly (measurements in inches in this article). You can measure this by using plastigage, which is a small thread of plastic that flattens out when comressed. By measuring the flattened plastic, you can tell how much clearance you have for your cushion of oil to live. Supposedly, the softer metal bearings are then just replaced when they wear out. Now, if you wear your crank out instead, since it is spinning inside the set of bearings, you may need to get a machinest to regrind and polish your crank and get slightly thicker bearings. I'd expect that the technology of bearings has matured a lot over the last 40 years. The link at the bottom does discuss some different schemes for the layering of metals in the bearings. The bearings are sold in .010 increments. So, say you have a STD engine. That is, it takes regular size bearings. If your bearings wear, and your crank doesn't wear, you could just get the bearings replaced. If the crank wears, then you make the metal on the crank where the bearing connects, the crank journals, smaller to the closest .010 increment and polish it. Now, the engine itself can be manufactured with differing sizes. It appears that our L Head 195.6, from the stamps, was standard, but the crank was ground. We had some STD bearings, that we got at auction, frankly, before we knew what we were doing. True, they were cheap, but if we don't need them they are only useful for learning. Now, it could very well be that our 440H could use them. We'll see. Anyway, I took some measurements on the bearings. Here is a measurement of the new STD rod bearing:
Here is a measurement of the old rod bearing:
It appears that these are .01 over, and that, at least with this crude measurement, that the bearings are not worn too much. Note that this measurement shows that the bearings are .005 over in thickness; however, the diameter of the crank has two of these bearings, one on each side. The rod bearings, at least, are marked .01 over:
Here is a picture of the old main bearings and a bearing cap. You can see copper on some of the main bearings:
Here is a picture of the rod bearings and a bearing cap:
Here is a page showing the use of plastigage:
Engine Rebuilding Project
|
|