QuestionQUESTION: We have a standard straight 8 (1402) with a rebuilt engine, starting for the first time. Each time it bursts the oil filter (we switched to a screw in). Backed out the spring at the oil pump, and that did not change the condition. Have not been able to get a pressure reading as we shut it down at sign of trouble. Pretty sure its way high. We did oil the engine with an oiler and circulated it pulling it down the street in gear and got pressure. Oil pump? or is it back pressure from a clog?, etc. etc. How to diagnose a clog?
ANSWER: Since you have a non-factory oil filter, I cannot tell for sure whether your problem is excessive oil pressure or a design problem with your filter installation.
To react to your idea that it is excessive oil pressure, the cause of this would be most likely a seized or improperly installed pressure relief valve. I would disassemble the whole pressure relief system and inspect all parts, and make particularly certain that all parts are installed correctly, and that the relief piston is free to move in the bore of the valve.
With a tight engine and cold SAE30W oil, it would be quite possible to have extremely high oil pressure on start up if the relief valve isn't working right. I think it is imperative that you plumb in a temporary oil pressure gauge so you can watch it as you crank the engine - it should not exceed 80 PSI - if it does, shut the engine down immediately: you definitely have a non-functioning relief valve.
Dick
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QUESTION: We removed the oil pressure relief valve assembly (unbolted from the side of the engine) and the piston does appear stuck, any tricks on removal of a stuck piston, it appears to be only accessible from the adjusting side and not the "oil side"? There is a large nut where the adjusting screw was threaded that almost looks like its part of the casting and is quite stuck also, does this need to be removed to access the stuck piston?
AnswerYou've definitely found your problem, I think. Whoever rebuilt the engine should have checked for this, it is a very common problem with all old engines.
To free up the stuck piston, I would first soak it well with PB-Blaster - a liquid wrench sort of thing you can find in any auto parts store (It's in a can with a yellow cap), and then when it has soaked overnight, try rapping it on a solid surface such as the anvil of a good sized bench vise, rapping in such a direction as to cause the piston to move outwards in the bore, and alternating directions back and forth until the piston moves a tiny bit. If you get it to move a tiny bit, just keep repeating the same process to see if you can get it to move further.
If doing this does not produce any motion at all from the piston, try putting the whole assembly in your oven at whatever it's maximum setting is for a few hours, then let it cool to room temp, and after that put it in your freezer overnight. When it is still very cold, try the rapping again - that should be the best bet at getting it apart.
Of course the threaded nut should come loose also, and getting it loose has to be a good move. Use an impact wrench, with the assembly very cold.
You must not use a tool to force the piston out, even if removing the nut allows you to see the backside of the piston. The machined clearances are VERY TIGHT in there, and any force on the parts can deform the parts such that the piston won't seal in its bore the way it is supposed to. Try to coax it out of the bore without using any direct force on the piston.
If all the above fails, take the assembly to a machine shop and ask a skilled machinist to have a try at getting it apart - he has tools that will not damage anything and experience in using them.
Good luck.
Dick
