Here's the story on my 850 thus far:

[jimross]

So I got this 850 I've been tinkering on and off with for the last (almost) 2 years or so, and I just can't figure out what the problem is:

It will run good for a while, then it will start kickin out of both ends and smoking, the bad kind (white). So, I took the head off, replaced the valve seals, and the head gasket, and put her back together to see if that was it.

Same problem.

So, upon inspecting the cylinders I see that one hasn't seated properly, but the compression test showed it was in spec.

Could a cracked oil ring still give me the proper compression reading? Cause there was no visible damage to the cylinder wall.

Also I have not adjusted the valves yet, could this also be a problem? (I don't see how since it's oil smoke)

Thanks guys.

[flyingace]

I think the general thinking is that smoke at startup that goes away is the result of valve stem seals. Smoke when the bike is warmed up and under accleration is rings.

[jimross]

so would you suggest perhaps another compression test? I admit, it's been a while since I first did one. And if I do it and it's in spec, would the oil ring still give me a good reading on compression? And furthermore: would this cause the firing out of the airbox and back?

[terry]

Your oil rings have no bearing on the compression test mate, so yeah, you can have a buggered oil control ring and a nice compression reading. In fact, if the oil control ring isn't doing it's job you might well have a higher number because the additional oil on the cylinder wall might be sealing any gaps between your compression rings and the cylinder wall.

Backfiring thru your airbox sounds to me like incorrect valve clearances, I see you haven't done that for a while and our bikes suffer quite badly from valve recession, so it's quite possible that your inlet valves aren't completely closed when the mixture is ignited. Checking the clearances is a piece of cake, so get that done mate.

Also it's easy to be out a tooth on your exhaust cam sprocket, the picture in the workshop manual lies, the pointer should be pointing a tad below the gasket sealing surface, not slightly above. Correct valve timing certainly makes a difference to performance, too. Cheers, Terry.

[jimross]

hey thanks a lot brother, I'll definitely look at the timing, and clearances as well.

[minimag79]

Your oil rings have no bearing on the compression test mate, so yeah, you can have a buggered oil control ring and a nice compression reading. In fact, if the oil control ring isn't doing it's job you might well have a higher number because the additional oil on the cylinder wall might be sealing any gaps between your compression rings and the cylinder wall.

Backfiring thru your airbox sounds to me like incorrect valve clearances, I see you haven't done that for a while and our bikes suffer quite badly from valve recession, so it's quite possible that your inlet valves aren't completely closed when the mixture is ignited. Checking the clearances is a piece of cake, so get that done mate.

Also it's easy to be out a tooth on your exhaust cam sprocket, the picture in the workshop manual lies, the pointer should be pointing a tad below the gasket sealing surface, not slightly above. Correct valve timing certainly makes a difference to performance, too. Cheers, Terry.

I know that this is a huge guess, but you may consider looking at your carb settings. I recently attended aircraft mechanics school, and one thing they taught us there is the fact that if the carbs are set too lean, backfiring through the carbs may happen.