Bearing Surfaces, Dowel Pin Holes, Thrust Surface And More
The first thing you must do is to look at the top of the engine case where the oil cooler is mounted. Look for a number stamped into the flat area ranging from .020 to .080 (i.e.; .020 .040, .060, .080) If no numbers are present, the case has not been machined before and is "Standard" (STD) (a GOOD SIGN). If it has numbers stamped in it, this is the amount that the main bearing saddles were bored oversized from STD. The lower the number the better. Personally, if this number is 020 or higher, I walk. I have nothing against align boring per se, I just want minimal boring. These days align boring is industry acceptable up to .080" oversized. I would not recommend getting a used case with a number higher than .040 Since when you get it the surfaces cleaned-up, may be too big for bearings. If you're starting with a case that's higher than .040 you could have yourself an ex$pen$ive door stop.
Here's where you need to let your fingernail be your guide. Above is a photo of a center main bearing with normal wear. Note the 2 discolored groove lines that run around the surface. Give it a good feel by running your fingernail across the ridges. If it catches (even slightly) it should be align bored. This is where you need to take into consideration the number stamped in the top of the case. If you have a .020 or higher you can't afford too much wear. You should also lay a long straight edge in the bottom of the main bearing bores and check for case warping.
The above photos are of the area there the crank pulley spins in the case. Feel it with your fingernail. If there are any grooves or ware at all in this area, put it down and walk away. Grooves here are often signs of an engine run with a bent crank or a loose crank pulley. This area is what the machine shop uses as the guide for the align boring. If it's worn, you can't align bore the case correctly!! The LEFT photo is of a BAD surface (Note the grooving going around the bore; this is BAD). The RIGHT photo is of a good case (it may not look obvious, but it's butter smooth).
Look for another number stamped on one of the main webs on the front of the engine case. This number is the amount that the thrust surface was machined from STD. Above are three photos of the THRUST surface of the front main bearing. In both cases, In the first photo you'll notice a severe groove (pounding) on this surface. The second photo shows a less severe (rebuild able) thrust area. The third shot shows a good thrust. The less of a groove, the better. You also, would again have to take into consideration the number stamped in the top of the main web on the case. If you have a .020 or higher you can't afford too much wear on the thrust surface.
The above photos are showing the small dowel pin holes in the main bearing saddles. The first shot shows an oblong dowel pin hole that is pretty much wasted. The other shot shows a good dowel pin hole. If the pins are still in the holes, give them a wiggle. There should be very, very little side to side movement.
Your next steps should be to inspect the lifter bores and distributor drive pinion bore. The LEFT photo shows one of the 8 lifter bores. If possible, slide a lifter in each bore and check for excessive play. Very little play should be detectable. The RIGHT photo is of the distributor drive pinion bore. ensure it's not elongated. If it is, walk away.
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Revised: August 29, 2003
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