Low oil pressure - im looking for clues
Posted: Wed Nov 17, 2021 3:00 pm
Greetings-
I am refurbishing a 1982 R100RS with 40k on it. I am new to BMW, but learning as I go. I have determined that the bike has low oil pressure through the use of 2 different gauges, screwed into the oil pressure switch hole. I generally see ok pressure at idle when cold - 30psi, that increases to 60psi at 2500 and maybe 75psi at 3000rpm. Not exactly spec pressure, which I understand to be more like 110-115psi. When warmed for a few minutes, the pressure at 1k idle drops to 15psi and holds.
Sussing out the situation: no drips or leaks or sight of any oil on or under the engine area, period.
Oil levels are always measured when input into the motor, the proper volume is used and checked when cold and warmed.
Remove valve covers - there's oil present there, even after cleaning it out and performing more psi tests.
Remove/ground spark plugs, hit starter and I see a slow ooze of oil from the rocker arms, both side the same. Not ideal volume, but there is oil getting to there.
Oil filter inspection - I have removed/replaced filters, twice over, with new folding filters and white/black O rings, and shims. The shoulder step depth on the motor is 3.0mm average. I tried using 1, 2 and 3 of the 0.3mm shims, with and without the paper gasket; I'll spare you of the o ring math and say that the pressure readings were the same (low). I inspected the ball valve at the inside wall of the filter's cylinder, it is there, on its spring, and I managed to plunge it a few times with a long wooden tool.
Sump and pan - drain semi-fresh oil, captured and inspected for anything, nothing was found. Remove sump screen and bolts to the motor. I replaced the gasket under the sump armature, and reassembled the strainer, its clean of debris, torqued to spec. I removed the worn gasket on the pan, scrubbed the mating surfaces clean, and fitted a new gasket, replaced the pan, torqued all of the bolts, patterned and tightened.
Overpressure valve under the engine cover - removed all alternator and wiring and rotor, and electrical to get behind to the area. I applied a heat gun to the valve area where it is screwed into the engine to free up the locktight, managed to unscrew it from its 40 yrs of home. I found no clues there either, the plunger works freely, the spring is in good shape, nothing stopping it from doing what it does. I have a replacement spring on order from Bob's, just because why not.
Oil cooler - the lines appear to be original, I am also replacing the 4 crush washers at the valve end of the fittings, but seeing how the cooler is not used at startup and only once warmed, I doubt that there is leaking in the cooler unit and lines.
Now that I have covered the bases- I will divulge this:
I replaced both of the oil pump rotors myself, following Brook Reams' Youtube channel, as his moto is the same. The oil pump is the version without the woodruff key, it has the machined flats on the inner part. The outer rotor does not seem to have a preference as to orientation, but the inner one has a slight chamfer on just one side of those flats. After searching for clues across the internet, I caught another video from Boxer2valve whereby William notes that the chamfered side faces towards the engine. For the life of me, I cannot remember which way I put it in, probably because at the time, it didn't seem to me, or Brook, to matter. I put on a new red o ring, and replaced the cover, and went about rebuilding the rest of the motor.
So, one question here is - would the facing orientation of the inner rotor matter - and would that likely lead to lower oil pressure? I do remember it sitting flush to the outer rotor, so why are the chamfers there?
I'm not looking forward to digging down to the oil pump, because that means flywheel, clutch and probably transmission out, which is a huge job.
I am hoping for clues or tips on things to do from here, or, I'll set out to do the dig to the oil pump if necessary.
much appreciation in advance -
porter
ps - all parts used were from Bobs.
I am refurbishing a 1982 R100RS with 40k on it. I am new to BMW, but learning as I go. I have determined that the bike has low oil pressure through the use of 2 different gauges, screwed into the oil pressure switch hole. I generally see ok pressure at idle when cold - 30psi, that increases to 60psi at 2500 and maybe 75psi at 3000rpm. Not exactly spec pressure, which I understand to be more like 110-115psi. When warmed for a few minutes, the pressure at 1k idle drops to 15psi and holds.
Sussing out the situation: no drips or leaks or sight of any oil on or under the engine area, period.
Oil levels are always measured when input into the motor, the proper volume is used and checked when cold and warmed.
Remove valve covers - there's oil present there, even after cleaning it out and performing more psi tests.
Remove/ground spark plugs, hit starter and I see a slow ooze of oil from the rocker arms, both side the same. Not ideal volume, but there is oil getting to there.
Oil filter inspection - I have removed/replaced filters, twice over, with new folding filters and white/black O rings, and shims. The shoulder step depth on the motor is 3.0mm average. I tried using 1, 2 and 3 of the 0.3mm shims, with and without the paper gasket; I'll spare you of the o ring math and say that the pressure readings were the same (low). I inspected the ball valve at the inside wall of the filter's cylinder, it is there, on its spring, and I managed to plunge it a few times with a long wooden tool.
Sump and pan - drain semi-fresh oil, captured and inspected for anything, nothing was found. Remove sump screen and bolts to the motor. I replaced the gasket under the sump armature, and reassembled the strainer, its clean of debris, torqued to spec. I removed the worn gasket on the pan, scrubbed the mating surfaces clean, and fitted a new gasket, replaced the pan, torqued all of the bolts, patterned and tightened.
Overpressure valve under the engine cover - removed all alternator and wiring and rotor, and electrical to get behind to the area. I applied a heat gun to the valve area where it is screwed into the engine to free up the locktight, managed to unscrew it from its 40 yrs of home. I found no clues there either, the plunger works freely, the spring is in good shape, nothing stopping it from doing what it does. I have a replacement spring on order from Bob's, just because why not.
Oil cooler - the lines appear to be original, I am also replacing the 4 crush washers at the valve end of the fittings, but seeing how the cooler is not used at startup and only once warmed, I doubt that there is leaking in the cooler unit and lines.
Now that I have covered the bases- I will divulge this:
I replaced both of the oil pump rotors myself, following Brook Reams' Youtube channel, as his moto is the same. The oil pump is the version without the woodruff key, it has the machined flats on the inner part. The outer rotor does not seem to have a preference as to orientation, but the inner one has a slight chamfer on just one side of those flats. After searching for clues across the internet, I caught another video from Boxer2valve whereby William notes that the chamfered side faces towards the engine. For the life of me, I cannot remember which way I put it in, probably because at the time, it didn't seem to me, or Brook, to matter. I put on a new red o ring, and replaced the cover, and went about rebuilding the rest of the motor.
So, one question here is - would the facing orientation of the inner rotor matter - and would that likely lead to lower oil pressure? I do remember it sitting flush to the outer rotor, so why are the chamfers there?
I'm not looking forward to digging down to the oil pump, because that means flywheel, clutch and probably transmission out, which is a huge job.
I am hoping for clues or tips on things to do from here, or, I'll set out to do the dig to the oil pump if necessary.
much appreciation in advance -
porter
ps - all parts used were from Bobs.