R80GS '92 - Oil lamp comes one when slow down
 

I have a R80GS '92 model with a 1000 Siebenrock conversion.

Starting up and riding all fine. Once the engine is hot and I come to a stop the oil lamp comes on. When I pull away the lamp does off again.

Have fitted a new oil filter and increase to 20W50. I also replaced the oil pressure switch. Problem persists.

Any immediate ideas?

I had the bike on the market but with this problem word has got around and the bike now comes standard with a "barge pole".

As I am stuck with the bike I am now thinking of using the opportunity to carry out a rebuild over the next for months/year and thereafter go further to a sidecar rig. Just in time for my daughter to be old enough to ride with us. I have spotted Shadow Raven's thread for motivation...

If you check the distance between the canister and engine-block it might give us a clue:
http://www.actiontouring.com/pic/oildist.jpg
If you lay the bike on the ground it's possible to do the measurement without draining the oil.

When you change the filter you should not use a paper-gasket but maybe a shim or two. The white o-ring should be changed once in while.

Have a look at the wiring for the oil pressure switch and the alternator charge warning lamp. May just be a crossed feed or minor short.

You can often rent oil pressure check guages which would prove/disprove low oil pressure at idle.

I think that the oil pump also has a high pressure bypass - ball bearing and spring arrangement - its so many years since I had an R series pump in bits that I am probably wrong - anyway check that the ball is seated.

Sounds like you have an oil bypass problem (perhaps filter canister as described above) You need to get an oil pressure gauge and pipe and adapter and and check the physical oil pressure

...poor oilpressure gauge?
...too old, too thinn, oil?
...too low oil-level in the oilpan?
Or... could be a missplacing of the o-ring and shim under the oilfilter cover...

This is why an hydraulic oil-pressure gauge is helpful:
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oil light on
 

have you checked that the oil filter is in the right way around ?:oops2:

As Alibaba points out this is a problem that needs checking, my r80gs did the same as you are saying the problem first appeared after covering over 80000 miles and it turned out the canister sleeve in the oil filter chamber had with time recessed - causing a drop in low rev oil pressure - ignore it at your peril - it ended up being a full engine rebuild for me everything needed replaced as the low oil pressure destroyed almost every component. It sould have a measurement of between 3.2 and 3.8mm max. It can be re-sleeved if it turns out to be the problem and a temporary (or depending on your mindset - permanent) repair to add an extra shim to the end of the canister if this is the problem. Follow the link to see the problem and the repair.
[url=http://www.motoren-israel.com/product_info.php?info=p299_Oelfiltermantelrohr-erneuern.html]

I had the same problem with an old kawasaki,
ie., under 1500revs the oil light came on, when hot.

variously suggested to me to change the oil pump/ strip engine/ and lots else.

changed the pressure sensor (pressure gauge), luckily cheap, and the simplest to do first.

problem sorted
bier

Change the white o-ring...i.e $2000 O-ring EVERY time unless you have a damn good reason not too. If it fails, your engine oil pressure fails. For the cost of it...it's cheap insurance.