Clogged oil galleries - -Change the oil.
This is probably old news to the more experienced folks here but this shows the importance of changing the oil frequently as well as demonstrating the need to use high quality oil.
I am in the process of rebuilding a junkyard engine that I bought about eighteen months ago. I heard it run before I purchased it and it was smooth and quiet and didn't smoke. Regardless, the plan was to rebuild the engine before installing it into the car and I'm glad I did. The engine has been apart before - it has an undersize crank and there is gray silicone sealer all over the engine. The heads looked as though they were rebuilt as well because the valves and seats were in excellent shape.
Anyway, when the bare heads were in the parts washer I took the washer hose and forced some solvent through the oil galleries to flush them out. Everything was going well until I noticed there was no solvent coming from the camshaft bearing lubrication holes on the two end exhaust cam bosses.
Further investigation revealed the oil gallery that feeds the exhaust cam was plugged on each end. It was plugged past the cam bearings on each end of the head which means these cam bearing surfaces were not getting any oil and it had not gotten any pressurized oil for a very long time. It was plugged about three inches into the head (almost to the center bearings) and the crud was so hard that I used a drill to clean it out. I guess it could be described as very dark brown crap with the consistency of epoxy - perhaps not that hard but hard enough that trying to rotate a screwdriver through the stuff was to no avail. The experienced folks will know what I mean.
Surprisingly enough, the cams nor the head was scored at all. There is a little more clearance on the end bearing surfaces than there is on the three middle bearings - a little but not much. It seems the entire camshaft load was in fact being carried by the three center journals. The journal with the most clearance is on the opposite end of the timing belt which I found to be interesting. Perhaps it was the one that clogged first.
According to plastigage, I am right at the .003 in limit for clearance. I am amazed that so little wear took place with the total lack of oil pressure to these journals. It seems there was enough splash lube to help get things oiled.
Lastly, just because things have been to a machine shop for repairs doesn't mean that all is well. My thought is to check everything to insure their work is ok. This three inches of crud in this head didn't build up overnight and I'm assuming that it was there when the heads were rebuilt by the previous owner of the junkyard car - - but they didn't flush the oil galleries during the process.
I have a few pics but for whatever reason I could not paste them here.
Anyway, just what I found..............thought it might be of interest to some of the folks in here.