I have a well travelled 1991 r100g with 95000 miles on the clock. The oil presure light has started coming on after the bike has done a few miles. it is only on up to around 1500-2000rpm then it goes out. apart from that the bike runs fine and no funny noises, at least non that were not there before. This has only started happening after a recent oil and filter change, but that could just be coincidence. just to be sure, i have changed the oil again and checked the filter is fitted correctly but everything seens fine. i also changed the pressure switch just in case it was a faulty switch. the light is still coming on. any suggestions on what to do next, short of stripping the engine?
grateful for any suggestions

What kind of parts did you fit after the oil-change (shims and gaskets)? Normally you should not use the gasket and you might need one or more shim.

the light should not come on at all after starting unless possibly idling ( 1000 rpm) on a very old motor in very hot conditions. never at 1500 rpm.

Just a small thing, it is the oil light and not the charging light?

sometimes the pressure relief spring breaks, or the assembly comes loose. I would take out the filter and have a good look in there. also check no old bits of old O ring have been left behind. I am pretty sure you bike is later than the $2000 o ring models ( unlike mine )
you could also either ask motobins.com or post a message here B O X E R W O R K S . C O M | Dedicated to 50's through 80's BMW Motorcycles
good luck

Do not operate the engine while this fault remains.

Disconnect the oil pressure switch and check the oil light does not come on (with the ignition on and engine kill switch err in the position ready for starting - the battery light should be on .. but oil light off). If the oil light is on then you have a wiring problem - a short some where between the oil light and the switch ..

If that is ok ...

I'd re re check the oil filter.. even put in new gaskets and shims around the filter. Still no good .. take it to a mechanic .. on a truck. Have them test the oil pressure ( gauge - real numbers) and see what they think. If you have been operating the bike with this fault you could be up for another engine.. $$$

__________________
---
Regards Frank Warner
motorcycles BMW R80 G/S 1981, BMW K11LT 1993, BMW K75 G/S

There might be a lot of reasons that the oil-pressure is low, but because it happened after an oil-change it’s likely to believe it is related to this.

First of all, the white o-ring inside the cover serves to purposes:
1) It seals so the oil would not leak out of the cover
2) It seals so the oil would not leak from the canister (the pipe you put the oil-filer inside) to the sump.
#1 is pretty easy to spot because there will leak oil around the cover, #2 is impossible to see and it will reduce the oil-pressure.

The O-ring has to be compressed to work; it is 4mm thick and should be compressed to3.0 – 3.3 mm. The way to measure this is:




If you measure more then 3.3 mm you have to use shim(s) to increase the compression on the o-ring (shim=0.3mm). If you use the papergasket you reduce the compression on the o-ring and you might get a bigger internal leak (#2) but you want know it!
If you measure less then 3.0 mm (not likely) then it’s okay to use the papergasket (or you might crush the o-ring) but otherwise don’t use it because it camouflages internal leaks.
It’s smart to change the o-ring once in while.

So why bother about this when your engine has been working for 95000 miles?
Because the canister tends to move over time, mine has moved twice and the last time the distance was 4.6mm!!
If you have this problem (or want peace in mind) you can get a new canister made in the correct length so it bottoms in the engine (no place for movement).

Of course before you do this you check that you have filled the right amount of oil with the correct viscosity and of course that it is the oil-pressure warning light that lights up.

Other possible solutions could be:
Worn oil pump
Worn housing around oil pump
Front main bearing out of position
Worn bearings (main and conrod)
Faulty cam-chain tensioner

Most of these errors develop over time, so I would check the canister and o-rings first.


I like to fit an oil-pressure gauge on all my vehicles and see the variations over time. Then I know what’s normal and can start to worry if the pressure drops. It’s hard to know afterwards, you might measure 3 bar at a specific rpm and temperature but how do you know what’s right?

thanks for the comprehensive replies!
I've done plent of filter changes before but I will check the canister/oil filter area again over the weekend just to be sure and clean the sump filter in the last hope that I can get away without a big bill. if not its off to the workshop (by truck) and brace myself for the bill. bugger!

I stopped running it when the light came on so maybe I will be lucky.
thanks again, i will post the outcome.
Paul

Yep .. oldbmw could have it right ... something to check ... it is after all 'just' another red light.

__________________
---
Regards Frank Warner
motorcycles BMW R80 G/S 1981, BMW K11LT 1993, BMW K75 G/S

That's a nice clean instrument panel setup with the HPN fairing AliBaba!

__________________
Ekke Kok

'84 R100RT 141,000 km (Dad's!)
'89 R100GS 250,000 km (and ready for another continent)
'07 R1200GS Adventure 100,000 km (just finished Circumnavigating Asia)
[SIGPIC][/SIGPIC]

www.ekke-audrey.ca

Thanks!
It’s a combination of HPN-design and my own design.

Had a good poke around the oil filter today and found the oil filter bypass valve has come unscrewed, almost to the point of coming off,( it’s a sort of donut shaped screw with a little bearing on a spring gubbins). I have screwed in back in and everything seems to be ok, the oil pressure light is going out on starting and staying out. I guess the spring wasn’t being compressed enough, allowing the oil to circulate without passing through the filter, causing a drop in pressure. Has any one ever come across the bypass valve causing a problem, I have never heard of anyone having a problem with it before!

I have tightened it all the way in, but I am not sure if this is right as there seems to be a line marked in the casing that may have to be line up, but I can’t see any reason why this should be the case. I can’t find any information anywhere on the valve. If anyone has any knowledge of this please let me know.
Thanks
Paul

Thanks for the update!

That was a new one (at least for me).
The only info I can find is that the spring should be 16mm and the ball should be 8 mm. The valve should open at 1,5 bar (over the filter).

Glad you found it. is always worth testing this bit when you change the filter, as I said they have a habit of coming off, sometimes the spring breaks. It is one of teh few parts I would recommend carrying on a rtw trip.