Mysterious Oil Disappearance

[Guest]

Goodday fellow GSers. I have been experiencing crankcase oil loss that has me befuddled with my limited GS experience. I am going through crankcase oil at about 1 litre / 800 kms. (1 qt/500 miles for you Mericans and Brits :-)) My 1979 GS1000 has no oil leaks whatsoever....doesn't burn blue at startup and doesn't blow blue smoke when I crank on it...even at sustained speeds of 180 km/hr. I can't see any oil leaks at all...anywhere! The GS runs very well, lots of power, nice and smooth and handles very well for an old bike. I have just recently soaked the topend with GM upper cylinder cleaner for a couple of hours through the spark plug holes (just incase there was a stuck ring or oil ring) sucked it out then ran the bike fairly aggressively for 200 kms. It runs a little smoother but still is consuming more oil than I think it should. Any suggestions from you Gurus out there? Am I not seeing the forest for the trees on the GS? The bike has 48000 kms on it.

[JamesWhut?]

Compression or leakdown test?

[tkent02]

Meh, some burn oil. Some don't. Oil is cheap.

[azr]

It'll all be going out the pipe, where else can it go? Don't worry aboit it, you're getting a bit better than my 78' 1000. Sounds lime the bikes running just fine. By the way, you do know they'll do 200km/hr right??

[oregonjake]

Yes, but don't you wonder why? My 1979 CB750 DOHC used a quart in 100 miles with no sign of leaking or burning. There was the usual oil ooze and seep but nothing that would account for that much oil loss. Everything checked out to be within factory specs, leakdown test was within tolerance and there was no indication at all of what would cause oil loss like I experienced. I consulted all the mechanics I know and they said, almost to the man that "yep, you got a problem but I don't know what it is."

I see a quart loss in 500 miles a bit excessive but within what I would tolerate. A quart in 100 miles? I sold the bike with the admonition that I could not find an oil leak. I wished the new oowner good luck and never heard from him again. I still wonder about that bike, tho...

[oregonjake]

With no noticeable smoke? Really? Wouldn't there be oily residue on the inside of the pipe that would show when you ran your finger in the opening?
I am skeptical, to say the least.

[Sandy]

You can burn quite a bit of oil without seeing smoke or fouled plugs. My bet is 37+ year old valve seals. As it's said "Been there, done that."

[Def]

It'll all be going out the pipe, where else can it go? Don't worry aboit it, you're getting a bit better than my 78' 1000. Sounds lime the bikes running just fine. By the way, you do know they'll do 200km/hr right??

Lol... yeah but with a Vetter trunk on it, it wobbles like a duck at 180 kph :-)

[Def]

Compression or leakdown test?

Yes... I think that will be my next course of action. I will however, soak the upper cylinders one more time with the Upper cylinder cleaner and give it a good run....then a compression test. A buddy of mine will help with the leakdown test if I still haven't defined the problem... thanks for your responses.

[oregonjake]

That goes against my learning over decades. Can you explain how much oil would have to be burned before seeing smoke? I would think a quart over 100 miles would be seen if burned, or am I wrong? I agree with valve seals being a possible culprit but again, wouldn't there be enough oil leaking past the seals to show as smoke? I am still skeptical. No offense.

[Sandy]

Mine was using about a quart in 600 miles before I did the valve seals and I never noticed any smoke on start up or while running. The only signs where a bit of smoke out the pipe on long over runs and only noticed by friends directly behind me. Otherwise the bike ran perfect with no deposits on the plugs and still good compression reading. Now it's about a quart in 2500 miles.

[oregonjake]

Hmmm...ponder this I must. I had asked friends of they had seen any smoke from the CB750 and they always said no. Maybe they were just being nice, I dunno...

[Grimly]

Mine burns about a litre per 400 miles. Meh; I'm not too bothered - it was better, but shows no signs of getting worse, in its retirement, so it can stay as it is until then.
Otoh, I had a car that burned a litre every 100 miles. It didn't produce choking clouds of smoke, but a very light blue haze could be seen in the rear view mirror in the long view of an undisturbed road. ie, hardly anyone else would have seen it, unless they were in direct line of the back of the car and light was just right. With new rings, that car went back to hardly using any at all.

[Brendan W]

I was at a litre per 400 miles. There was a little smoke at start up, the plugs were filthy, oil was leaking from the front of the headgasket, the tensioner, the clutch rod seal and and and............
Both boots were getting coated in the stuff to the point where the right boot slipped on the road at stop lights. My jeans and the back tyre knew about it as well. Everywhere I went I left spots on the floor within seconds of stopping.
Since sorting it out the consumption looks more like a litre per 4000 miles.
How you can have that level of loss with no external signs is a mystery. Are you sure a 'friend' isn't coming over at night and removing some
Out of interest what oil are you using ?

[tkent02]

My 750 burns about as much, runs great, can't ever see any smoke. Not too worried about it. I'll fix it when I put the 1100 engine in it. If I ever get around to it.