MG Car Repair: 75 mg midget oil pressure, oil pressure gauge, cam bearings

Question
oil pressure drops from 55lbs to below 10 lbs after car runs for 10 to 15 min. As water temp rises the oil pressure goes down ,,i have replaced oil pressure valve and installed new filter ,i have removed valve cover and watched oil flow over rockers ,but its not alot as i have seen on other cars of a diferent make,[ford,chev,ect.. car sat for 8 years , has only 44 k for miles motor does not knock or ping when running,compression is 150 on all cly , , motor does smoke when 1st started , please tell me what you think ?? Brent from brentsboats.com

Answer
Hi Brent,
Oil pressure is the direct result of the resistance of the oil being forced through the bearings. The oil pump has the power to pump in excess of 400 PSI so a pressure relief valve with a strong spring is installed in the block. (which you replaced spring and valve) This valve regulates the pressure down in an attempt to maintain 45 to 65 PSI running and about 25 to 35 PSI at idle with hot oil.

If you brought the car to me in a shop I would first check that that you were using a name brand oil and at least 10W 30 (in a low mileage engine) and that you have used the correct filter for the engine (Triumph 1500 engine in your case) Then I would connect a known good hydraulic oil pressure gauge in the block to confirm the oil pressure readings.

If the readings were confirmed low, I would remove the pan and "Plasti-Gauge" several rod bearings and the center main bearings to check oil clearance. (.0015" to .0025" on the main and .0015" to .002" on the rods) The other place that you can loose oil pressure is the cam bearings (less likely as even worn cam bearings will not loose that much oil pressure.

Your oil smoke when you first starting is valve guides. If you have blue smoke out the tail pipe on hard acceleration or on a quick shift (As viewed from the rear watching the car go) is rings. Neither have anything to do with oil pressure.

You said the engine only had 44K on it. An engine rebuild means many different things to different people. My question is, was the crank turned and under size bearings installed? and were new valves and guides installed?

Howard