I have to do a search but found no answers…

My bike is a BMW R80GS Basic with 153.000 km on the clock.
It has an oil-pressure meter and it used to indicate somewhere between 4 and 5 bar at normal engine-temperature. At low revs or at idle it will now drop to 1.5 bar, maybe to 1 bar if the engine is really hot. When driving in higher speeds (80km/h) the pressure normally creeps above 4 bar. This change has happened slowly during the last 60.000 km but it doesn’t look like it has become worse for a while.

So the big question is: How far can the pressure drop before it gets dangerous?

I guess I have to open the engine, is there anything special I should be looking for other then?

-Oil pump
Check clearance.

-Metal-filter in oil-sump:
Should be okay. If it’s clogged it would have been worse on high RPM.

-Main-bearings and conrod-bearings
Might be worth changing them if I check them anyway

-Maybe the relief spring behind the camchain?
I’m not sure if this spring is before or after the pressure transmitter.


The oil I use is mineral oils of different brands, 10W40 or 20W50 dependent of temperature.

Hi, not sure what the oil pressure should be but if your oil pump had failed there is very little time between this event and a damaged crank. My oil warning light on my R100 came on at exactly the same time as the big end started to knock. What oil are you using, this could have an effect on oil pressure, also if the bike has done an extreem high mileage the main bushes may be worn allowing oil to by-pass the crankshaft, also it is possible that the oil pressure gauge is faulty. not much help I guess. I would be supprised if you find lumps of metal in the sump without having heard loud banging noises first.

My best guess is that the oil pressure drop is normal for the mileage - in other words, the engine is well-worn, therefore the pressure is low. Loose clearances=lowered pressure.

Rod and main bearings would be the main thing in need of repair in this case, judging from what you say.

It's POSSIBLE that the oil pump is worn badly enough to drop the pressure, but it would be unusual. Of course it should be checked as part of a full rebuild.

If the engine is not making noise, do a compression check, and if it's very good I'd run it for a while yet, so long as it sounds good and the pressure doesn't drop significantly below what you have now.

DO have a qualified airhead BMW mechanic listen to it.

------------------
Grant Johnson

Seek, and ye shall find.
------------------------

One world, Two wheels.
www.HorizonsUnlimited.com

__________________
Grant Johnson
Seek, and ye shall find.
------------------------
Inspiring, Informing and Connecting travellers since 1997!
www.HorizonsUnlimited.com

Thanks!
I think the sensor is working beacuse it shows normal pressure when the engine is cold. The sensor is mounted on a long pipe so it's not affected by the heat. It also shows that the pressure increases with 4-5 bar when entering a cold river (sensor above water) so it makes sense....

Maybe the pressure is normal for the mileage? It might be, I had hoped to get that confimed here :-)
I guess I will change the rod and mainbearings this winter. They are not expensive anyway.

I haven't meassured the compression but I think it's okay because it feels healthy and I have rebuild the tops and changed the rings. One of the rings was broken, probably for a long time, but the cylinders and pistons were well inside tolerances.

Hmmm, maybe it's time to realize that the bike is not a youngster anymore... The drivshaft finally broke too after 153kkm:-)

How did it go with the oil-pressure ?

My R80 was overhauled at 140 000km. The oilpressure went from about 4-5bars to 8bars with the new oil-pump. Currently I have 7-8bars at operational speeds and 1-3bars at idel depending on air-temp, engine temp, and engine oil. The engine has only run 200 000km by now.

Did you change the oil-pump back in 2003 ?

__________________
Drive Safely,
Albert

Well, I used the bike as it was for approx 25 kkm after the initial post before the oil-pressure got so low that I decided to do something.

Basically I found:
-The canister (around oilfilter) had moved inwards and caused an internal oil-leak
-The locking pin for the front main bearing was missing (it had been missing for more then 170kkm) and the front bearing had moved pretty much.
-The oil-pump was worn (but not much)
-The housing around the oil-pump was worn

The engine is now rebuilt with other mods like siebenrock 1000ccm, ported tops and another camshaft and it works like a dream. 25kkm so far…

I see you have 8 bars pressure and if that’s at around 100°c I think it’s on the high side, at least compared to the spec and my bikes.

Never heard that the oil-filter canister can "move". Interesting! Did you find the cause of this ?

It was almost jack-pot on oil-pressure affecting possibilities! - -

How badly worn was the main-bearing seat, and the oil-pump housing?
How did you solve the oil-pump housing enlargement?

So if 7-8bars at operating temp is too high, how high should it be ?
I get this pressure in the oil-cooler loop, so it will be giving a slightly different pressure as to where the oil-pressure gauge is installed from factory.
I get these pressure at 120-130'C which seems to be the operating temp on my bike (also measured in the oil-cooler loop). Two days ago when I went to Söderköping (210km south of Stockholm - mainly freeway) I had 7bars at ca 120km/h, 135'C, Biltema Sverige new 0W-50 fully synthetic (crap) oil. I usually use Omega 757 20W50 - will change to that in a while, just "flushing" the engine with this "cheap" oil.

Which cam did you choose, 324', 320', other ?
I've tried getting some data on the cams - none available besides marketing claims. Is there any Dyna tests showing the true difference between the cams ? Most interested since I have a R100RT on my mc-lift/table for overhaul - not sure how much to do to the engine. Run 160 000km and runs very well; it just the constant lubrication of the frame and engines out-side that I need to fix, studd grummets are... and the cam-chaing cover is... I've put in a new oil-pump and new crank-seal (the seal that was installed was very wrong but had nevertheless held-up for over 100 000km(!). The gearbox is overhauled and HPN +5% and -6% sprockets are installed. New splines in the final drive.

__________________
Drive Safely,
Albert

It’s rare but it happens from time to time. The canister is press fitted but it does not bottom out so it might slip inwards. I think it’s most likely to happen on a overheated engine or if you suddenly cool a very hot engine (rivercrossing or washing)
I have no fabricated a canister which bottoms out so this will not happen again.



The front bearing had moved and was pretty bad, the rear bearing was spot on!
The hole for the oil pump housing was machined bigger and a collar was fitted. Israel Motor did this work

I wouldn’t say it’s something wrong but the relief valve should be completely open at 5 bars and in my experience the pressure seldom goes over 5 bar on a hot engine. These pressures are measured before the filter but I have no idea about the pressure-drop above the filter.
But if it had been like this for a long time I wouldn’t have worried.




This is a rather difficult area; there are also different cams with the same name…
I was looking for maximum low-end torque and installed a 296° camshaft (and a Siebenrock 1000ccm and ported tops). The result is very good; the bike runs like a train below 5500 rpm.
There might be an article about it (with some dyno-charts) in a Swedish magazine early next year.


Sounds nice!
It might be an idea to check the piston-rings.

When replacing the oil filter you should always measure the depth of the canister from the gasket surface area.
For models up to 85 the measurement must be between 3.2mm and 3.4mm
On models from 85 the measurement must be 3.6mm to 3.8mm (No gasket must be fitted)
If the measurement is bigger the gap must be spaced by fitting more spacers behind the white O-ring.

I used multiple shims for a while but I didn’t like this setup so a friend’s friend made a canister with the correct length:

Will do that. Still contemplating what to do; new conrod bearing, balansing the conrods and pistons, new piston-rings, current pistons vs Venolia 10.5:1 that I have collecting dust or new lightweight siebenrock..., new valves and guides, convert to unleaded seats or not..., stick with 44/40 vs 46/38..., BugPack high-flow vs Manley..., dualplugging vs not..., there is a lot to consider -

I do have 14bars with Biltema fully synthetic 5W/50 engine oil at around +10'C the first few minutes. If I rev it hits 20bars or there about during the first few seconds after starting. When the engine is warm I have about 6.5 bars now, but it used to be 7-7.5bars - figures using cheap oil, the viscosity is deteriorating fast now after 1000-2000km something. I'll soon change to Omega 757 15W/40; just "cleaning" the engine with the Biltema synthetic.
With Omega I am used to have about 8 bars with the engine at operational temp and 4-6bars at idel. With Biltema I have about 1-1.5bars at idle now... it held about 3bars when the oil was new and the temp was about 20'C in the air.

Friend of mine have also 6-7 bars at 90-100km/h with operational temp on the engine. His hydraulic gauge is attached to a T-joint at the oilpressure switch. His gauge needled is bent due to high oil pressure...

__________________
Drive Safely,
Albert