Oil pressure

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I finallly have my 1930 132 ci engine back together after two years work. The car starts and runs fine now but it has 40-50 psi oil pressure initially which drops to 30 after a few minutes. However after driving about twenty minutes the oil pressure gradually drops to 5-10 under load. I started with a cracked block which we had heated and welded. We then had to re line bore the block. We replaced the pistons, rings and had the cam which was badly pitted restored to factory specs. We rebabbitted everything. When reassembling everything, it all went back together better than factory specs except the cam bearings which were slightly over spec but better than when we started. The oil pressure relief valve has a new spring but I can hand tighten it to almost maximum by hand which makes me thing the relief valve isn’t tight enough.

I have received advice from a number of people ranging from everything is normal to you have a major clearence issue in the engine allowing too much oil flow. We have taken the engine apart once already and everything is getting oil even with the low pressure. Currently the engine is back together and I am not anxious to take it apart again. However, I don’t want to damage the engine either. I am looking for any advice about normal oil pressure and possible problems and remedies.

Jim Nicholson 30 EDL Model A

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Jim,

What kind of oil filter system are you using. These engines are designed for a bypass type of system and not full flow.

Bill

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What oil are you using?

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The filter is a partial flow with 1/16 opening. We reduced it from 1/4. It made no difference. We have straight weight 40 in it.

Jim

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Just for ‘grins’ hook up a different oil pressure gauge and see if it agrees with the in-car gauge.

Next try a different spring in the pressure relief valve, or shim it up.

What were your oil pressure readings before the rebuild ??

And waht temperature is the coolant running at? 160* or 190*?

Pressure does sound low, but there are several things to check yet.

Greg L

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I discussed the oil pressure problem with Jim. Considering all of the work that has been done on the engine, the best way to locate the problem is to drop the oil pan and use a pre-oiler to pressurize the system which will show any internal oil leak(s) which can be the cause of the oil pressure problem.

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Thank you all for the advice. To answer Greg’s questions, we tried a different gauge and it confirmed the readings, I added a longer , heavier spring to the pressure relief valve and it made no difference but did seem to screw in too easily all the way plus two shims. I have never had the engine running pre rebuild as the block was cracked when I bought it. The coolant is around 160. My best guess at this point is to take the pan off and pressure test the oil system as Paul suggests.

Jim

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Sounds to me like a pressure pot will not find the problem. If the pressure only drops after a long time and is that low under load, something strange is going on. I don’t understand all the work and new bearings and running the old cam bearings. It’s possible the oil filter is set up wrong and not using the correct oil ports for the lines, or you still have a crack in the block that openes up with temperature. Also, was the proper shim installed on the cam along with the oil slinger? The oil dump for the timing chain could also have been modified. This will be a difficult problem to overcome due to the high engine temp issue. It is always best to NEVER weld a block, ever. Stich repairs are ok in some places, but it may be worth your time to get another block, most parts will change over, and you can then put in new cam bearings, if lucky, the new mains will scrape in. Ed

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With all due respect to Ed, I’ve had good luck with a pre-oiler in finding internal engine oil leaks. Just use SAE 10 to simulate the viscosity of the engine oil when it is hot. Considering that the oil pressure regulator doesn’t respond to different spring settings. it would be a good idea to see if the leak might be there.

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Hi Paul, no problem, It’s just that from the description of the pressure drop, and it’s in a known block that had cracks, I think that it is possible or probable it won’t show. It goes from high pressure cold to a normal pressure drop when warm, then an almost 66 percent drop under load. I would think that it’s not likely to be obvious of where the problem is until the motor is thoroughly hot. It may be that the test should be rigged so that it’s possible to drop the pan after the motor is hot with only a few pan bolts. But there is the danger of severe burns. This situation is a good example of running a motor in on a dyno if at all possible, or in the chassis without any hood / fenders, et in the way to be sure there are no problems. Working on a finished and assembled car with problems like this just seem to cause paint and body damage along with lost time. If memory serves me I ran my 36 V-12 for at least 6 hours in the chassis, and it suffered two lifter failures and one exhaust manifold crack. They were easy fixes while it was just a bare chassis. I hope that luck is with Jim and it’s an easy fix. My best, Ed.

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