I went thru this exact same thing with a J-4 I restored a few years ago and after weeks of trouble shooting I replaced the accessory case and that solved the problem. The problem was that when the oil got hot the pressure would drop because of the worn out accessory case.
We have spent several days trouble shooting the problem and here is what has transpired.
The engine has 24 hrs SMOH and did not exhibit any problems when Frank flew it to Lock Haven and back. He reported an oil temp of 130 degrees (cooler weather) and solid oil pressure of 30 and above.
I flew the plane Sunday for thirty minutes and the oil pressure never got above 20 lbs at cruise ( I flew until the temp reached 180). When I landed the oil pressure went to zero. The engine had Phillips 20W50 oil in it.
We pulled the oil screen and it was clear, we pulled the pressure relief valve and noticed that it had one of the new blue and smaller springs in it (about 40% smaller than OEM). Also the face of the valve was rough. We polished the face of the valve and replaced the spring with an original in excellent condition (no washers). We also changed the oil and replaced it with Aeroshell 50 wt detergent.
When we restarted the engine we immediately got 40 lbs of pressure vs the 25 we had before. I flew the aircraft 45 minutes and the oil temp finally reached 180 degrees and stabilized. The oil pressure remained solid in the green, and 35 to 37 lbs. at cruise vs the 20 lbs I had previously, even when the temp reached 180 degrees.
Then when I landed the oil pressure again dropped to ZERO at idle.
Our next step is to put a temporary oil gauge in the plane and fly it to see if the Cub instrument is malfunctioning at idle. I have heard that these old instruments will sometimes read low at idle when the oil gets hot. If the 2nd gauge reads the same then the next step will be to pull the engine and replace the accessory case.
The outside air temp here has been around 95 degrees every day.
Will keep you posted,
Best Regards,
Steve
We have spent several days trouble shooting the problem and here is what has transpired.
The engine has 24 hrs SMOH and did not exhibit any problems when Frank flew it to Lock Haven and back. He reported an oil temp of 130 degrees (cooler weather) and solid oil pressure of 30 and above.
I flew the plane Sunday for thirty minutes and the oil pressure never got above 20 lbs at cruise ( I flew until the temp reached 180). When I landed the oil pressure went to zero. The engine had Phillips 20W50 oil in it.
We pulled the oil screen and it was clear, we pulled the pressure relief valve and noticed that it had one of the new blue and smaller springs in it (about 40% smaller than OEM). Also the face of the valve was rough. We polished the face of the valve and replaced the spring with an original in excellent condition (no washers). We also changed the oil and replaced it with Aeroshell 50 wt detergent.
When we restarted the engine we immediately got 40 lbs of pressure vs the 25 we had before. I flew the aircraft 45 minutes and the oil temp finally reached 180 degrees and stabilized. The oil pressure remained solid in the green, and 35 to 37 lbs. at cruise vs the 20 lbs I had previously, even when the temp reached 180 degrees.
Then when I landed the oil pressure again dropped to ZERO at idle.
Our next step is to put a temporary oil gauge in the plane and fly it to see if the Cub instrument is malfunctioning at idle. I have heard that these old instruments will sometimes read low at idle when the oil gets hot. If the 2nd gauge reads the same then the next step will be to pull the engine and replace the accessory case.
The outside air temp here has been around 95 degrees every day.
Will keep you posted,
Best Regards,
Steve
