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Low oil pressure - im looking for clues

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 »

bremoit wrote:
Tue Nov 30, 2021 7:20 am
Had the experience of the oil pressure relief valve failing/coming apart causing oil light to come on at idle. Its a rare failure but it happens.
Are you referring to the piston and spring affair located next to the timing chain? I have inspected that, it looked clean and in working order. I am swapping the spring because it is cheap and I have no reference on how strong it should be.

The only other pressure relief valve I can think of is the ball on a spring that is located at the bottom end of the oil filter canister cavity. That too I inspected, poked with a stick and saw that it was evident and at least plunging a little under pressure.

thanks for the advice -

bremoit
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Re: Low oil pressure - im looking for clues

Post by bremoit »

Yep, that one next to the chain. Mine had come apart and needed replaced...so unlikely the issue for you. But yes, just throwing it out there since you are lookin for clues.

jnclem
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Re: Low oil pressure - im looking for clues

Post by jnclem »

I’ll be following this thread to see what you find out. I’ve been trying to track down a low oil pressure problem on a 1989 R100gs for several months. I’ve done most of the things you’ve done, but my issue, or issues, are a little different. I thought I’d relate what I’ve done just to add to the general knowledge on this thread. I apologize in advance for the length of this post.

I first discovered I had a problem on July 4th this year. I was riding over a local dirt pass, and when I got to the top after about 40 minutes of slow climbing on an 85-degree day, my oil pressure light started to blink at idle.

My bike is a GS, but it doesn’t have an oil cooler. It was removed sometime before I got the bike. I’ve had it for 9 years, and it has always run very well. I don’t know what the depth of the oil filter canister was, but the O-ring has always come out properly flattened at every oil change. I’ve always used 1 O-ring, and no external gasket.

When the light started flashing at idle, I first checked the O-ring, since it’s such a common place to find a problem. The ring was perfectly round – not good. I found that the canister had shifted. It was too deep and not centered. It measured anywhere from 4.6 to 5.1mm depending on where you measured it.

Like you, I put a couple of different oil pressure gauges on it. I found that it would start up cold with 105 psi (that should have told me something), but as the bike warmed the pressure would drop, ending up holding just over 10psi/1000rpm. I will say here that my brother is a fairly well known and highly respected airhead mechanic that has been working on these bikes since the 1960’s. Somewhere along the way, he recalls reading something from BMW that referred to the fact that these engines should hold a minimum of 10psi/1000 rpm of oil pressure, so I have used that as sort of a base level. Mine would idle at 12psi at 1100 rpm when it was good and hot – after running for say 40 minutes or more in summer temps. It would hold something like 36 or 37psi at 3500rpm, 42psi at 4000rpm, etc.

At that time, I also checked the oil pressure relief valve under the timing cover. I did not remove it, and probably should have. I did find that I could spin the plunger if I put a little pressure on the spring. It looked ok, and I was convinced the canister was the real problem, so I left it alone.

I took the bike up to my brother’s shop, and we did several things. We pulled the rod bearings, which looked fine, but I put new ones in since we were there. We replaced the oil pump. We did find evidence that it was quite worn, and some scaring on the case behind the rotor indicated that the engine may have had some metal through it sometime in its life. We used a stack of 5 shims, and it seemed like things were better, but after a short time, it was clear that the oil pressure was still low. Neither of us considered that a permanent solution, but thought we’d give it a try.

On a second trip to his shop a couple of months later, we replaced the canister. Unfortunately, I gave it about one tap too many, and ended up with it in just shy of 4mm. I had wanted to set it at 3.5mm or so. So, now I am running it with 3 shims, and it is definitely better. It will generally run at about 10 to 15 psi above that minimum number when it’s hot. For example, at 4000 rpm, it might run at 55 to 58 psi. It still idles at 20 to as low as 15 psi when it’s good and hot. Not ideal, but I don’t think I’m harming the engine either.

Now, it still pegs my oil pressure gauge to 100 psi when I first start it. I don’t think it should do that since the relief valve is supposed to activate at 72psi or so. I have a new relief valve and spring that I will install next spring. We have about 1 or 2 more days here in the riding season before we get serious snow. I don’t have a warm place to work on it, so I’m not going to deal with it until spring. I plan to measure the new spring against the old one. I think that the valve is stuck, and possibly the spring is worn out. One of my brother’s guru friends says that he has seen several of these springs get weak and cause problems in recent years. I am hopeful that replacing that valve will bring the pressure back up to where it should be. I’m not confident that I would see the numbers I see now on a hot summer day on a slow climb in the mountains.

So, a very long story, but it is hard to find much information on this subject, especially when the answer isn’t simply someone installing the O-ring improperly, or using the wrong oil. I had a very hard time finding someone who had ever actually replaced a canister, but there are a few out there willing to share information.

I would be very interested to see what you find when you check the length of the relief valve spring in yours. The Haines manual actually lists a length for that spring. That manual isn’t always totally accurate, but if you could compare your old one with the new one, I’d like to know what you find.

Good hunting, and thanks for posting your results.

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

Post by P-Funk »

I'll answer the above post first, then move on. Thanks for the long post, everything helps!

I purchased a new valve spring - it is visually identical to the original, which has not even changed in color. The compression force is the same, perhaps slightly firmer, so I have replaced it anyway. I put a dab of locktite on the threads and installed it. I haven't re-assembled the cover or alternator stuff, because I have been working on the pump swap.

I am now reassembling the motor, it is alot slower than the dismantle.

I found two odd things once I reached the oil pump. One was that the bolts were not totally tight, they were firm, but not loose- and it was all of them, which I find weird, as I tend to over tighten things.

Also, and I think that this is the source of my low oil pressure problem - the O-ring looked fine at first, but when I purchased the replacement, I noticed that it was different. The one I was using is black and thicker, while the new one is red and thin. The old one measures 0.11". I think that the new one is about 0.075". Perhaps oil was bypassing the seal on the cover side of the rotors? All of my parts have been coming from one of 2 dealers, so I am not sure how I got a strange part like a thick O-ring. It fits in the groove perfectly, but it is out of spec from what it should be.

Remember when I was all concerned about the chamfer on the inner rotor? The one that was in the motor has chamfers on both sides, so orientation does not matter. The outer rotor has a notch on the outer rim, I think that is an oil scraper of sorts. I oiled up and installed both parts as they are basically new, I cannot fathom that replacement parts would be any different. I checked the bore and passageways as best I could, shook a voodoo doll at it, and put the cover on.

The transmission is in, new bolts on the rear drive hookup, torqued. The rubber boot can suck an egg, I am furious at how long it took to put that on. I have the rear wheel axle in, and alot of electrical ahead of me before I can test out the pressure again.

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schrader7032
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Re: Low oil pressure - im looking for clues

Post by schrader7032 »

It looks like Brook used the orange o-ring per his info about middle of this page:

https://brook.reams.me/bmw-motorcycle-r ... -flywheel/
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2
Fast. Neat. Average. Friendly. Good. Good.

jnclem
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Re: Low oil pressure - im looking for clues

Post by jnclem »

Thanks for the information on the spring. I do hope I find an issue there when I do mine. We've done everything else so… How did you remove the relief valve? Did you heat the case then use channel locks or the like on the outside of it, or did you remove the stud that is in the way for using the slot in the end of It?

I’ve been riding my GS at every opportunity since riding this late in the year is extremely rare here. We live at 8000’, and most local rides take us another 1 or 2K higher. Anyway, with the temperatures around 50 at the highest, and somewhere in the 30s as the sun drops, my oil pressure is hanging in there. But I’m not confident that it will be sufficient next summer.

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

Post by P-Funk »

I heated the threaded area of the spring's outer cylinder with a heat gun, it takes a while as there is alot of metal there.
Then, I clamped vice grips on the non threaded end, because I heard that the middle area can collapse. To break any thread lock material, I tapped the end of the vice grip with a small ball peen hammer. It took about 5 tries but it slowly came free.

jnclem
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Re: Low oil pressure - im looking for clues

Post by jnclem »

Good information. Thanks.

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srankin
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Re: Low oil pressure - im looking for clues

Post by srankin »

Stuff like this makes me wish the airhead guru Oak was still alive and writing his article. He was the only reason I stayed an Airhead Club member. Once he was gone, and I had to deal with the two forum moderators, I quit the club.

I like Snowbum but, get a headache reading his stuff. I am VERY happy he wrote it but...

This is an interesting thread, and I am really learning a lot as you work out the solution. Good luck, good hunting. 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 »

It is time for an update.

I managed to complete the task of re-attaching all of the wiring in my custom loom- this enabled me to run the starter motor, in the hopes of verifying oil pressure. I have the pressure gauge still attached, and with the spark plugs removed, and no gasoline present anywhere, I was able to use the ignition key switch and turn over the motor, I had also recently charged up the battery. For the first 5-7 seconds, the starter motor spun freely, without laboring, but then as I was watching the gauge, the oil pressure began to rise, and the starter motor changed to a lower pitch, slowed slightly, and began to churn away as the oil pump began to pump. The gauge ran up to 85psi quickly, and I only held it there for one more second, then stopped.

I consider this to be a great sign- it verifies that I have successfully put the pump back together, that the clutch and flywheel are properly installed, and that my electrical system is connected correctly - no small feat when it is all custom wired.

But most of all, it showed me that my huge problem of low oil pressure is now rectified. I look forward to buttoning up the rest of the motor, I have the timing to set with the optical trigger at the front end of the crankshaft. Then, I will replace the tank, hook up the gas, and move the bike outside in order to start it up and check the idle, oil pressure at higher rpm, check all of the lights, buttons, and dash functions. Who knows, maybe even a ride in the neighborhood, to see if anything is loose or amiss.

So, TL/DR: Upon disassembly, the oil pump cover had an O-ring under it that was too thick, yes it fit well, but it created a gap area between the rotors and the cover, allowing oil to mix between openings, and therefore, the pump only created some pressure, but not up to psi expectations. My hypothesis is also: that as the oil heated up, the mixture flow increased, especially at lower rpm. I now have the stock red O-ring under the cover, which measures 0.075" in thickness.
Because I am a newbie, and I was sold this thick O-ring by a dealer, I did not suspect that it would make a huge difference, so I swapped it in, replacing the original from 1982.

Once I have completed the buttoning up and testing - I'll be back to update of any changes to this scenario.

Many thanks to those who chimed in with advice, tips, help offers and encouragement.

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