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Low oil pressure - im looking for clues

P-Funk
Posts: 15
Joined: Wed Nov 17, 2021 2:20 pm
Location: baltimore suburbs

Low oil pressure - im looking for clues

Post by P-Funk »

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.

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schrader7032
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Re: Low oil pressure - im looking for clues

Post by schrader7032 »

Welcome to the forum, Porter! Thanks for the run down on what you've tried. I kept saying to myself "check xyz" and then in a few sentences you did "check xyz"!

Not sure where you get 115psi from, but I think the oil pressures are nominally around 75 right after start up and then drop from there. Actually after reading Snowbum's page on the oiling system, that pressure relieve valve opens at 75, so no way will you get much more than that.

https://bmwmotorcycletech.info/oilingsystem.htm

Snowbum also indicates that idle psi is around 30. Your 15 is lowish, but I'm not sure it's freak-out low. Does the oil pressure light ever come on at idle?

Also, when did this concern for oil pressure start? Before or after the oil pump rotor replacement?
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2
Fast. Neat. Average. Friendly. Good. Good.

P-Funk
Posts: 15
Joined: Wed Nov 17, 2021 2:20 pm
Location: baltimore suburbs

Re: Low oil pressure - im looking for clues

Post by P-Funk »

Does the oil pressure light ever come on at idle?
Yes, intermittently. And while driving - hold on there, I was only warming it up in my neighborhood, nothing over 20mph, never left 2nd gear.
Your next question might be the switch, and yes, I have swapped it and reverted back to the original, both show sometimes on the idiot light in the dash, which is wired correctly.
Also, when did this concern for oil pressure start? Before or after the oil pump rotor replacement?
After. I drove it mildly for almost a year, never far away. I saw the oil light on at startup, but then turn off as I revved up and got going. I never saw it on past that.

For comparison - here is Brook's pressure test that shows 85 at a chugging startup, and 115 above 2k rpm.
https://www.youtube.com/watch?v=QDuxCY-DXHw
Again to reiterate - same model, same year, same rebuild parts.

I do appreciate your remarks, please keep pondering this, Im stumped.
Please don't make me read snowbums site again, I find it irritatingly long winded, akin to legalese.

porter

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schrader7032
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Re: Low oil pressure - im looking for clues

Post by schrader7032 »

Well, if the problem came up after the pump rotor replacement, then that's what you have to go back and confirm.
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2
Fast. Neat. Average. Friendly. Good. Good.

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cbclemmens
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Re: Low oil pressure - im looking for clues

Post by cbclemmens »

You did not mention the viscosity of the oil you are running. I run fully synthetic 20W-50 in all 3 of my airheads. If you are running lower viscosity that may be the source of your "low" pressure - although it's not all that low. I think the light comes on at about 7 psi. I don't know the answer to your oil pump assembly question but I would suggest that you could raise the pressure by draining a pint out of the crankcase and add back a pint of STP, Lucas oil stabilizer or a similar product.

Craig

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srankin
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Re: Low oil pressure - im looking for clues

Post by srankin »

Not to be a jerk but, it looks like it is time to go back and check your work.

Sorry, I can't add more to the post, good luck. St.
Owner of a 84, R80RT and 78, R100RS

P-Funk
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Re: Low oil pressure - im looking for clues

Post by P-Funk »

The oil being used is Liqui moly 20w-50.

No jerks here yet, I get that the pump is worth inspecting. BUT-
I want to cover anything that I am missing because I want to avoid the work, if possible.

If I have to, I will disassemble.

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srankin
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Re: Low oil pressure - im looking for clues

Post by srankin »

I understand, it does not hurt to look for other problems, who knows, maybe another problem existed before and led you to working on the pump? Not to say you fixed it for nothing, LOL, I am being a jerk again.

This is a real head scratcher, at least you are getting some decent information and ideas where to look and steps to take.


Yeah, it is a pain to take out the transmission and stuff but, less a pain than doing new bearings on the engine. I didn't pay attention to where you live but if you are close to me, it is coming up on bloody winter and there will be plenty of time to pull things apart. My garage and lift is available for a short time if you need a hand. I am not the best mechanic in the world but an extra pair of hands makes things go faster. Cheers, St.
Owner of a 84, R80RT and 78, R100RS

P-Funk
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Joined: Wed Nov 17, 2021 2:20 pm
Location: baltimore suburbs

Re: Low oil pressure - im looking for clues

Post by P-Funk »

Thanks for the kind offer for the lift and hands, but, I am in Baltimore Md.

I went to the pump to fix a leaking rear main seal, and I scrubbed and re-lubed the splines there. I found the rotors to have visible scars, so I swapped them out for new.
All along, I had the help from an experienced BMW rider, I sent pictures and texts at every step, and followed his advice, as well as videos, and my clymer manual.

I will order the parts and set out to get down to the pump, once again.

thanks
porter

Carott
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Re: Low oil pressure - im looking for clues

Post by Carott »

Porter,
Several other new owners of BMW airheads have had concerns about low oil pressure at idle only to realize that the red light is actually the alternator charging light.
Airheads are known for having the alternator charging light glowing at low idle speeds and the use of a red indicator light for this can be alarming.
Hopefully the solution could be this easy.
Best of luck,
Brett
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