Is my engine JUNK?

[drax]

1976 MG Midget with the 1500cc engine. PROBLEM: Burns oil, looses oil pressure, starts to clatter and dies after about 15 miles of driving.
I have 150 compression on all cylinders. Cold start I have 70psi oil pressure and NO noises. It was pushing oil out the dip stick tube so I disconnected the hose from the valve cover to the charcoal canister thinking too much crank case pressure, no more pushing oil. I drive it about 15-20 miles, engine temp 120 degrees and stays there but it starts to loose oil pressure, sprays oil out of every place possible starts to clatter a bit and dies. Let it sit 10 minutes or so and it starts right up, oil pressure back to 30-40psi and no noises. I have a Stromberg Carb, vented oil cap, electric fuel pump with the mechanical still in place but bypassed. I'm running 10W30 oil with a AC PF53 oil filter. Is my engine junk or am I missing something? PCV? Heavier oil weight? Different oil filter? I don't want to rebuild it if I don't have to. My engine guy say rebuild but I'm thinking maybe not. Too much crankcase pressure? Help please?

 

[drax]

One other note: I ran it the other day for about 25 minutes-did not drive it, just ran it up to temp, about 120 degrees. Oil pressure was 18 at idle and almost 30psi at 2000rpm. I could rev it up multiple times and never made a noise, didn't die, just burned a little oil. It seems disaster strikes only when driving.

 

[YakkoWarner]

I'm betting you have badly worn rings/cylinder walls, so when you're driving (which will yield combustion chamber pressures higher than just turning in neutral with no load) combustion gases are blowing past the rings and causing your crankcase pressure problem. I have a friend who had a 350 small block Chevy truck which exhibited the exact same problem, and it was worn rings/cylinders.

10-30 oil is a bit light for MG engines, normally 20-50 is specified. If the engine has been run extensively with that oil, that could explain the wear.
Unfortunately a rebuild of at least the bottom end sounds warranted - overbore the cylinders just enough to restore roundness, matching oversize pistons with the new rings. Or if you can find another 1500 engine in decent condition (from either a damaged/wrecked car or a car with cylinder head problems but sound bottom end) a transplant might be less costly. Some oil additives that claim to restore lost ring seal or compression might help in the short term, but I wouldn't count on that as a permanent fix. There really is no such thing as "engine rebuild in a bottle"...

 

[RickF]

Put the PCV system back together to at least reduce the oil leaks. When the complete system is in place it does an amazing job of reducing crankcase pressure and stopping oil leaks. It takes zero horsepower to run the PCV system so why disconnect it? The only smog device on these engines that reduces HP is the air injection system as it takes several HP to turn the pump. The rest of them are just along for the ride and help keep the exhaust cleaner.

 

[JPSmit]

I agree with the above, I run 20-50 in mine with a quart of Lucas Engine oil stabilizer. You can replace the oil pump in place and it is well worth doing (you would have to do it anyway if you are refreshing the engine) The new pump (available from Moss Motors) is actually from a Spitfire - same engine but the Spit has a better pump, longer intake so less likely to have oil starvation.

 

[sparkydave]

Agreed on 20W-50. Once ran 10W-30 in mine, and the oil pressure got a bit low when hot. Having just gone through a stalling problem when hot myself, check for vacuum leaks. My elbow fitting at the EGR valve had cracked, and the engine ran reasonably well until it got hot. I put a Mityvac on the fitting at the carburetor, and it wouldn't hold a vacuum.

I agree with the above, I run 20-50 in mine with a quart of Lucas Engine oil stabilizer. You can replace the oil pump in place and it is well worth doing (you would have to do it anyway if you are refreshing the engine) The new pump (available from Moss Motors) is actually from a Spitfire - same engine but the Spit has a better pump, longer intake so less likely to have oil starvation.

Interesting, the factory manual shows the oil pickup pointing straight down, as does the Moss catalog. Some time ago I had to replace my oil pan, and discovered mine has the Spitfire pump with the angled pickup in it, apparently that's what it was built with. I've always noticed that if I brake hard, I lose oil pressure even though it's full. I always assumed it was because I have the other pickup in it.

 

[drax]

Thank you all for the input. I'm going to try some of these recommendations and see what happens.

 

[SaxMan]

These motors do not like lighter oil. I had a partial bottle of 0w - 20 from my daily driver and I put it in my Sprite when it was a half quart down. It turned the Sprite into a smoke machine. With 20w50, the motor is a lot happier.