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Old 01-09-2007, 02:18 AM   #67
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Joined: Jul 2001
Location: Lausanne, Switzerland
Oddometer: 1,356
Eek NOT the $2000 O-Ring -- or: Prevent that oil leak


here's a short write-up of an almost fatal kind of "movement" that I encountered a few weeks back. May the seal be with you:

At about 143000 km on my 1990 R80GS, after a holiday trip in Italy, I was coming back from a very short ride - something like 1 km to the washing place and back. The bike was barely on the centerstand when I noticed a trace of oil behind me. This was not just a few droplets - it was a real oil leak.

First I thought it was the gearbox neutral switch, but the smell of the oil was clearly that of motor oil. I roughly wiped off the excess oil, and re-started the engine. The oil pressure warning light behaved as usual, i.e. it went dark right after starting the engine. Letting the engine idle, I carefully observed the engine block.

Oil was bubbling out at the front of the oil filter cover - !

I switched the engine off, and dropped the bike on the sidestand. I removed the oil filter cover and found all three bolts to be firmly in place, and the oil filter as such was also in good shape. The most important item, the white O-Ring (aka "the $2000 O-Ring"), also was in the correct shape: slightly compressed. What was it then that caused this leak?

The question was answered by measuring the distance between the outer edge of the oil filter tube (aka canister) and the flat surface of the engine block (since an image says more than a thousand words: is a diagram at the HPN website, with annotations in German). In the past, I had always found something like 3.8 mm here, which is just the perfect distance so that the white O-Ring is compressed, but no additional shim nor seal is required. Yet ... the value that I measured now was 4.2 mm. This meant that the tube had settled, the O-Ring with its 4.0 mm diameter would not seal anymore, and oil - as well as oil pressure - was lost.

Technically, the issue could be solved quickly by inserting a suitable shim from an earlier oil change (yes, I keep those ) under the cover, just above the (new) O-Ring.

However, what strikes me is that this movement of the oil filter tube occurred "out of the blue", after more than 140 Mm and 15 years, without any warning. Would I have been on a trip, it was highly probable that the loss of oil - and of oil pressure - would have gone unnoticed until it was too late

Edit/Add-it: The oil pressure warning light was off all the time (but, yes, it definitively works ).

Thus, my recommendation: Measure the distance between the outer edge of the oil filter canister and the flat surface at the engine block every time you open the oil filter cover. And, from time to time, keep an eye on that area to see if it is still dry.

Edit: Finally an oil change where I had the camera at hand ... here's a picture that shows the crucial detail:

- Joerg

1990 BMW R80GS and K100LT * Lausanne, Switzerland
My Motorcycle WebPages - LED voltage monitor (aka charge light)

Joerg screwed with this post 05-13-2008 at 02:41 AM Reason: added info about red light
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