I swear, I have never seen an engine so hell bent on self-destruction in my life! For your reading pleasure, (It's long) take your pick between any of these problems… (For those not familiar with my previous post, Loose Wrist Pin, this a Pontiac 400 engine.)

One common denominator I am seeing in this tear down is the excessive wear, (IMO) possibly due to a lack of lubrication. This engine has about 1,000 miles since the second rebuild. Oil pressure is 20PSI hot at idle and close to 60PSI hot at 2,000 RPM.

#1. I can feel a ridge on the cylinders! The walls are already polished with only an occasional hint of the original crosshatch visible. They are KB hypereutectic pistons with moly rings and .003” clearance, according to the machine shop. He says that’s a “perfect” clearance. KB recommends .002” - .0025”. For supercharged, racing, nitro, etc., clearances can be up around .004” - .005”. So I guess .003” is OK, maybe a little noisy. I assume the higher heat in race engines expands the pistons more than a street engine. I don’t have the necessary tools to measure them myself.

#2. The rod and main bearings again seem to have more wear than normal. When I tore down the engine after it over heated, it had about 7,000 miles on it and the rod bearings were worn to the point of some of them were showing copper on the rod side. That was my bad for not investigating this more. Based on my Plastigage measurements, (I know), rod clearances and main clearances have increased by .0005 - .001”. Apparently, these clearances don’t affect the oil pressure. The oil pump had no wear to speak of. I couldn’t find clearance specifications anywhere.

I found that Melling doesn’t offer a high volume pump, just a high pressure. Since this pump can keep up the volume with these clearances I figure a high pressure one will definitely increase the pressure. BTW, I wonder if the oil gauge I used could be erroneous? I might do a bench test and run the pump up to its bypass pressure and compare different gauges.

#3. On the first rebuild two lifters had a narrow groove on their faces, which seemed to indicate that they were not rotating. I changed the cam and lifters. When I was troubleshooting this knock, some of them didn’t appear to be rotating. A rep at Comp Cams seemed to think it was an oiling issue. Upon teardown, no grooves were found. Funny looking wear patterns though. Using the side of another lifter as a straight edge, a random sample shows them to still have a crown.

I also tested them by installing the cam and a lifter with a pushrod and rotating the cam with my drill and putting hand pressure on the pushrods and they all rotated somewhat. Don’t know how scientific that is or what that proves… The cam lobes all have the same wear pattern too. Again, not what I would expect for a low mileage cam. I’m used to seeing wear across the nose of the lobes and then it narrows down as it travels toward the base.

#4 Finally, I have ½” slop in the timing chain. Too much? It’s a stock style, non-roller chain.