Oil pressure for 1925 9ton PA truck

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Rebuilding 1925 six cylinder, dual valve engine for 9 ton truck and oil flow seems too low when cranking (haven’t risked starting as I want to resolve this oil flow issue first.) What is the proper oil pressure I should expect?

Thanks for the help,

Matt

508 892 4354

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Use a oil pot before you fire it. I am not sure if that engine is partial or a full pressure system. Did you drop the pan? I would NOT fire the truck without removing the pan and cleaning it. You can also inspect the rods and the bores while you have it down. As a rule of thumb, 5 pounds per one thousand rpm’ is the lowest acceptable pressure. That motor probably maxes out at 2200 romp or less. I would want 30 lbs down the road with a hot engine, and 12 lbs or better at idle with a warm engine, otherwise I would start looking at the motor for issues. Post a few photos please! Ed.

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Hi Matt, I whole-heartedly agree with Ed. If you haven’t dropped the pan and cleaned it, I’d not risk starting the engine. When the pan is down, the oil pump can be removed and inspected, and the bearings checked, and the oil passageways in the crankshaft cleaned..

Once you have cleaned out the crankshaft, you then are safe to use ‘normal’ detergent oil available virtually everywhere. Without making sure the engine is not full of sludge and dirt deposited by non-detergent oil, it is a bit ‘risky’ to run the engine on detergent oil.

After the oil pump is inspected for scores and excess clearances, I’d pack the gears with vaseline, aka Petroleum Jelly when reassembling the pump. Even though this pump is a fully submerged pump, it will pump with virtually no pressure leakage at starter-motor cranking speeds.

Check the recently published Service Bulletins for an article about checking oil pumps for wear and excess clearances. Even though the oil pump in the Service Bulletin is a later oil pump, the areas to check for wear and proper clearances are the same.

These engines do not have an oil filter, only the screen at the inlet to the oil pump. Some very abrasive and damaging dirt can get through the inlet screen. With the high costs to rebuild the lower end on this type of engine, it is imperative that you feed it clean oil.

I’m not sure if that engine has the manifold-vacuum controlled oil pressure regulator or not. If it does, if it is operating correctly, it should with no intake manifold vacuum be allowing full available oil flow and pressure. If it is malfunctioning, it could be bleeding off oil supply and pressure.

With a clean intake screen, a well functioning oil pump, and good cranking speed from the starter, you should see at least 5psi oil pressure. I’m sure you are cranking the engine with the spark plugs removed and some engine oil or ATF squirted into each cylinder bore?

You can remove the oil line that goes from the engine to the oil pressure gauge, and put a different oil line from the engine to a catch-pan, When cranking the engine you should have a good steady flow of clean engine oil out of the line.

I hope the above information helps, feel free to contact me with any questions. We are in the same time zones. Check the roster for contact info.

Greg Long

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