Burning Oil - Valve Seal or Rings (Pictures)

[Jandrews]

My neighbor's 9 year old rides a little Kawasaki KLX 110. It is a great little bike, and he bought it right. When he brought it home, it smoked like a mosquito truck. He rode it for a few months knowing that we would go ahead and do a top end rebuild on it this winter.

Well, here we are. We have it torn down, and are now trying to figure out what the root cause of the oil burning is. The piston, cylinder and rings look great. No broken rings, no scoring in the cylinder etc... But the below pics are of the head. Obviously the exhaust valve is all crusted up with carbon, and the exhaust port is coked up too (see pics below).

So, we are going to go ahead and put a new head on it for $200, and call it good. This bike has very low hours, and we don't want to put more money into it than we need to.

My question is, once torn down, is there an easy way to tell what the root cause of the oil burning is? I was expecting a broken, or stuck ring, so when I didn't find that, and saw the condition of the head, I ASSUMED that the oil is getting into the combustion chamber via a bad valve seal/guide. Can this hypothesis be confirmed, or is that best done with a leakdown test prior to tear down?

Any thoughts?

Thanks,

JA

[Superman]

Hard to imagine that much oil flowing past the valve guides. Exhaust port sees mostly positive pressure, so it'd have to be the intake valve guide/seal. Plus.....if it were the exhaust guide/seal, the oil wouldn't get into the combustion chamber and the exhaust valve would look cleaner. These are just guesses.

I still suspect the rings. How wide is the ring gap?

[Jandrews]

Damn Supe....now you got me thinking.

I have not measured the ring gap yet. How do I do a full inspection of the rings to know what's right and what's not?

Also, why is just the exhaust valve all crusted up and the intake valve clean?

JA

[Zeke]

Probably the idiot that the boy bought the thing from thought you still had to mix oil with the gas. I would have soaked the head in carb cleaner and called it good. Well, maybe a little lapping compound.

[Jandrews]

Milt,

Do you have an opinion on whether the valves are the problem or not, based purely on what you can see in the pics? Maybe just do rings too and be done with it??

Thanks,

JA

[masraum]

Originally Posted by Jandrews

Damn Supe....now you got me thinking.

I have not measured the ring gap yet. How do I do a full inspection of the rings to know what's right and what's not?

Also, why is just the exhaust valve all crusted up and the intake valve clean?

JA

I'm going to guess it's because the unburnt fuel (and possibly oil) keeps the intake valve cool and clean, but the exhaust valve is hot, hot, hot and cooks the oil as it flows past which causes the cooked oil to build up on/in the exhaust side of the house.

I'm certainly no expert, but I think that the specs that you often see listed for rings are the end gap and clearance in the grooves (between the side of the ring and the edge of the groove that it's in).

[Superman]

To measure ring gap, you carefully take the ring off the piston (they are very brittle) and put the ring in the cylinder. The gap is where the two ends come nearly together.

[Superman]

Although......if this motor is getting a gas/oil mix but is designed for straight gas, then that's where all the smoke is coming from.

[Jandrews]

No, no...Milt speculated out of nowhere that the previous owner mixed oil and gas. There is no evidence or reason to believe that took place.

JA

[EarlyPorsche]

A bad valve guide can cause the oil burning like you mention. While you have it apart it wouldn't hurt to just install a set of new rings. You should be fine with new rings and a head.

[asphaltgambler]

That appears to be a lot of volume of oil in the combustion chamber - Really think it rings / oil ring lost tension due to overheating/running it hard while barely moving - or just plain worn out,.........

[stomachmonkey]

I'd start with rings.

We're talking probably $20 for a set so as long as it's apart I'd replace them even if I was 100% sure the issue was the head.

Button it back up and if it still smokes you've narrowed it down or saved $200, cause if it is not the head you're still buying rings.

[Jandrews]

Thanks everyone. You have convinced me to do the rings, which I sort of felt was right anyway. No issues with putting new rings into the original piston and cylinder? Assuming the piston and cylinder are reasonably good?

JA

[Superman]

The ring "lands" (the grooves in the piston) shouldn't be worn too wide. There is a spec. You can measure stuff, and then know. Frankly, a couple of new valve guides and a set of rings and you'd probably be good to go.

[john70t]

The test I was told:
A). Smoke on decelleration=guides. Extra manifold vacuum sucks it in past guide seals.
B). Smoke on acelleration=rings. Oil scraper ring can't keep it in the case, and the PCV dumps the case pressure from blowbye back into the manifold.

[LakeCleElum]

A "leak down" test before you took it apart would have given your answer.....If was mine and I had it already apart (and I've done plenty), I would:

replace rings and hone cylinder. (reuse piston if it measures OK).
replace valve seals.
lap valves.
measure guides.
(very rare for the guides to need replacing on these smaller Japanese motors - they go over 100,000 miles on the larger engine).

Parts are cheap on Ebay....I bought my grandson the little Kawa 65 2-stroke that had low compression.....bought piston/rings/pin for $40........

[asphaltgambler]

If it were me - I would bore and install the next oversize piston and ring set - still cheap. That way the top end will be in "Harmony"

[gr8fl4porsche]

If it were me - I would bore and install the next oversize piston and ring set - still cheap. That way the top end will be in "Harmony"

That's the way I always do it. If I bother to break it down, it basically gets a full rebuild. Good time to go through the gears and bearings as well.