Just completed about 20 miles in the Minor Semi-sports - the first post-restoration run. Everything great except the oil pressure. 110 psi from cold is excellent, but this reduces to 15-20 psi at a hot idle after about fifteen minutes of driving. The engine is newly rebuilt with crank grind and new white metal.
I am running straight 30 - should I use a thicker oil? Might I have an air leak somewhere? I have checked out the oil filter cap - fitted a spare and tightened it right down - no improvement.
I am running with a nut under the oil pressure relief valve spring because without it I was getting only about 65 from cold. That made a huge difference but not to the hot pressure.
Any thoughts?
Oil pressure
Moderators: Ian Grace, Will Grace
Ewan,
I think the pump itself is fine - it is delivering 110 psi on startup and this only drops as the engine warms up. After fifteen minutes or so, when it is running hot, then pressure is all but gone. My suspicion is that the relief valve is not seating well. I have been advised that the valve piston should be lapped in to the pump body. I'm going to try this, but removing the pump with the engine in situ is one of the more difficult tasks on a Minor. I may remove the track rod and drag link to give me easier access.
Originally, I could only get about 65 psi, and I know that a new engine should give at least 100, so I put a nut under the relief spring and immediately got 100+, so the relief valve is clearly playing an important part in the cold pressure.
I'll let you know how I get on in the next day or so.
I think the pump itself is fine - it is delivering 110 psi on startup and this only drops as the engine warms up. After fifteen minutes or so, when it is running hot, then pressure is all but gone. My suspicion is that the relief valve is not seating well. I have been advised that the valve piston should be lapped in to the pump body. I'm going to try this, but removing the pump with the engine in situ is one of the more difficult tasks on a Minor. I may remove the track rod and drag link to give me easier access.
Originally, I could only get about 65 psi, and I know that a new engine should give at least 100, so I put a nut under the relief spring and immediately got 100+, so the relief valve is clearly playing an important part in the cold pressure.
I'll let you know how I get on in the next day or so.
I have oil pressure! Andrew, you were spot on!
This evening, I removed the oil pump and stripped it down. I could see that the seat for the relief valve piston was not pitted, but it was worn in a peculiar way - an annular ring at about 2/3 the radius of the bore. So I replaced the pump with my spare, using the cover plate from the original pump as the one on the spare was very rust-pitted.
Of course, the ignition timing was thrown out since the gear on the oil pump engages with the distributor, but I retimed it and started it up - after priming the oil filter bowl, and noting that the mesh filter had all sorts of crud in it, which I removed! As the pump primed from the filter bowl, the pressure rose and settled at 80 psi - obviously the point at which the relief valve was blowing off (now without the nut under the spring). But the acid test would be the pressure at hot idle, so I let the engine tick over at a fast idle to get warm, then hot, and kept an eye on the pressure, which settled at about 75 psi. Eventually, the engine boiled merrily, the radiator gurgling and steam issuing from the overflow pipe and the calormeter needle hard over. Pressure about 65 psi. Reducing revs to a very slow idle, I could not get pressure below 40 psi, which I reckon is excellent.
So it was the unlapped relief valve.
Job done!
This evening, I removed the oil pump and stripped it down. I could see that the seat for the relief valve piston was not pitted, but it was worn in a peculiar way - an annular ring at about 2/3 the radius of the bore. So I replaced the pump with my spare, using the cover plate from the original pump as the one on the spare was very rust-pitted.
Of course, the ignition timing was thrown out since the gear on the oil pump engages with the distributor, but I retimed it and started it up - after priming the oil filter bowl, and noting that the mesh filter had all sorts of crud in it, which I removed! As the pump primed from the filter bowl, the pressure rose and settled at 80 psi - obviously the point at which the relief valve was blowing off (now without the nut under the spring). But the acid test would be the pressure at hot idle, so I let the engine tick over at a fast idle to get warm, then hot, and kept an eye on the pressure, which settled at about 75 psi. Eventually, the engine boiled merrily, the radiator gurgling and steam issuing from the overflow pipe and the calormeter needle hard over. Pressure about 65 psi. Reducing revs to a very slow idle, I could not get pressure below 40 psi, which I reckon is excellent.
So it was the unlapped relief valve.
Job done!
Hi Ian and Ewan, I've got a similar problem with my F type, which as you know is the M type/Morris OHC engine with an added 2 cylinders!. I have great oil pressure at startup (100+) to the point where the bypass activates, and will settle to about 70psi after a few minutes. If I then run the engine for 10 minutes or about 5-10 road miles, the pressure drops on tickover to about 5-10psi, although on the road it seems to maintain a regular 30psi at 35-40mph. The water temp having got to near boiling by this point (early F's run very hot at the best of times due to poor cooling design of the head)
My initial thoughts were the bigends, and although I've not removed the sump to check them, with the head off and using some general "engineering" checks, I cant see/feel any noticable bearing slackness. I'm wondering if it could also be the oilpump or even relief valve that's causing a problem. Any comments?
Regards
My initial thoughts were the bigends, and although I've not removed the sump to check them, with the head off and using some general "engineering" checks, I cant see/feel any noticable bearing slackness. I'm wondering if it could also be the oilpump or even relief valve that's causing a problem. Any comments?
Regards
MG F1 Tourer, Morris 8 Special and ex M type owner
Glenn,
I replaced my pump with another - after lapping the replacement pump valve as best I could. I now have about 80 pounds from cold (which is presumably the pressure at which the valve is blowing off - a little low - I typically get 100 psi from cold with a Minor engine. When I got back tonight from about a ten mile run (in 80 degree heat, I should add), I was getting about 25 at tickover. I would prefer to see this nearer 40.
This is on straight 30. I have been advised (by Dave Cooksey via Jeremy Evans) to use low detergent 20-50, so I plan to change the oil soon and see if this improves the pressure at all. I may also experiment with washers under the relief spring to bring the cold pressure up to 100 psi and see what that does for the hot pressure.
I'll keep you posted as to how things go. Hope this helps.
I replaced my pump with another - after lapping the replacement pump valve as best I could. I now have about 80 pounds from cold (which is presumably the pressure at which the valve is blowing off - a little low - I typically get 100 psi from cold with a Minor engine. When I got back tonight from about a ten mile run (in 80 degree heat, I should add), I was getting about 25 at tickover. I would prefer to see this nearer 40.
This is on straight 30. I have been advised (by Dave Cooksey via Jeremy Evans) to use low detergent 20-50, so I plan to change the oil soon and see if this improves the pressure at all. I may also experiment with washers under the relief spring to bring the cold pressure up to 100 psi and see what that does for the hot pressure.
I'll keep you posted as to how things go. Hope this helps.
Just changed the oil to regular 20-50. Cold oil pressure unchanged at about 68 psi - static at 68 whether idling or revving. At the same time I put two washers under the pressure relief valve. Cold pressure now 90 psi. Took the car for a run to get it hot - it is 90 degrees here in Michigan this afternoon, so it was at boiling point and just spitting hot water through the overflow pipe when I got back. Setting the idle as low as possible with the engine still running, pressure was 35 to 40 and blipped to 60, so I'm happy with both figures. It is surprising how much that spring affects the running pressure. Of course I was too impatient to check the hot oil pressure before adding the springs, so some of the improvement there (it was about 25 psi before) may be due to the 20-50.
Incidentally, the first time I screwed in the relief valve and fired up, I had zero pressure! So I checked the filter bowl - full of oil. Screwed it down hard. Still no pressure whatsoever. Then I checked the plastic bowl under the car full of the oil I just drained. Sure enough - there was the relief valve cup which had quietly slid out when I had my back turned! It is a difficult, filthy job screwing the valve back in under the car, and between the track rods - pushing it hard against the spring while trying to engage the thread with fingers dowsed in oil! I hope I don't have to do any more oil pump jobs for a while.
Incidentally, the first time I screwed in the relief valve and fired up, I had zero pressure! So I checked the filter bowl - full of oil. Screwed it down hard. Still no pressure whatsoever. Then I checked the plastic bowl under the car full of the oil I just drained. Sure enough - there was the relief valve cup which had quietly slid out when I had my back turned! It is a difficult, filthy job screwing the valve back in under the car, and between the track rods - pushing it hard against the spring while trying to engage the thread with fingers dowsed in oil! I hope I don't have to do any more oil pump jobs for a while.
Hi Ian,
Thanks for the detail, I'm going to strip the pump assembly this weekend to see what I can find, as this seems to be the likely candidate. I've run the car for the last 12 months on a 20-50 "Classic" engine oil. Originally it seemed to help the overall oil pressure, but i guess it has probably now aged, even though only running for about 450 miles, so will change that as well.. (after overhauling the pump so that I can see any change first!)
Regards
Thanks for the detail, I'm going to strip the pump assembly this weekend to see what I can find, as this seems to be the likely candidate. I've run the car for the last 12 months on a 20-50 "Classic" engine oil. Originally it seemed to help the overall oil pressure, but i guess it has probably now aged, even though only running for about 450 miles, so will change that as well.. (after overhauling the pump so that I can see any change first!)
Regards
MG F1 Tourer, Morris 8 Special and ex M type owner