If it smells like oil . . .

I've got one cyl that appears to be burning oil. Noticed some white/grey smoke coming from left exhaust pipe (1978 KZ650) during takeoff and my clothes smell like burned oil when I stop. So I pull the plugs and all look fine except for cyl #2 as it is semi-shiny black. Based on that fact, I would assume that cyl #2 is burning oil since it's on the left exhaust pipe. Compression test shows #1=135, #2=160, #3=140, #4=140. Based on those figures, I would assume Cyl #2 is getting oil which raises the compression more than the remaining cylinders.

My question is this: How do you determine if the oil is from the valve seal or rings? Is it possible that I'm missing something here? Any help would be appreciated.

Now that's an interesting question!
The normal method to determine if rings or valves are leaking is to do a dry compression test, then add oil to the cylinder and check again, but you already have oil in there. When does it smoke? On start up, steady cruise, slowing down?

By 'during take off' do you mean you get a puff of smoke at each gear change? If this is the case and it's not smoking while idling, it's most likely the guide seal.

Based on my limited experience (hobby car engine work) ring leak will give more smoke at idle when engine is hot and less while running at speed. Valve guide seal leak will give puff of smoke every time throttle is closed and then opened again. Bigger puff if a little engine braking is alowed to occur.

You could try a 'leakdown' test but my bet's on the guide seal.

You might also see if you're blowing any smoke out the breather which is more a ring or head gasket thing.

-Duck

I dont see any smoke when engine is cold, idling or cruising. I only notice it after idling for a moment then hitting the throttle to launch (typically at a traffic signal). It's possible it's slightly smoking during cruise but dont see any.

Duck. I think your right on here. It happens after throttling down and back on again so the guides are probably at fault. Will see if I can get hold of a leakdown tester or make my own. Question. How can I determine if smoke is coming from the breather since it's connected to the stock airbox? Guess I could disconnect and watch closely while accelerating from stop. Is there another approach?

I tend to agree with Duck that it is likely to be a valve guide seal, especially considering that the rubber in thge seal is now 20 years old.

I posted an article in the Filebase a few days ago on how to build a Leak Down Tester and and how to use it.

No need to check breather. That's gonna smoke from rings or bad head gasket. Your symptoms point to guide seal.

-Duck

Thanks a bunch guys. I'll check the filebase and let you know the results of the leak down test. The repair manual shows replacing the valve guides require special tools to punch out/in. Are there any tricks to replacing it without purchasing a special tool or going to a shop?

I would have to say it is valve guides. Oil in the cylinders is going to help seal the rings and raise compression reading. Rings are never going to seal 100% your allways going to have blow-by.
I think that when you do a compression test for bad rings its a difference of 70% of your highest presure reading.

Haven't done on your particular engine.
If you're tight for $, have a look at the 'special tool' and how things go together, once you've got it apart. You might be able to put together something suitable with a trip to plumbing/hardware store. You might also find something at the autoparts store that will do the trick and not cost as much as the 'special' tool...tupically it's just something that guides and pushes the seal into place. It's easier if it's slippery...

-Duck

I think you misunderstood what was said, it's valve seals, not guides, that are probably at fault.
Valve seals are a whole lot easier to replace (and a lot cheaper too) than valve guides.

Yes, I did misunderstand and thanks for clarifying. So the valve stem seal can be replaced with only the valve spring compressor tool but would it not be beneficial to replace the guides at the same time? Looks like an APE guide set is $60 USD and labor estimates are $65 to $90 from reputable machine shops in this area. At what point should the guides themselves be replaced or how to diagnose if they are worn?