Rebuilt engine smokes bad, why

[jwalsh965]

Just finished rebuilding a yamaha g2 engine and it smokes like crazy. its a splash oil system so why would it smoke so bad. Compression is perfect, engine starts right up everytime. It smoked bad before rebuild so what am i missing.

[CP241]

Was it smoking for a long time before rebuilding it? Did you check ring end gap in top/mid/bottom of the cylinder before you put it together? Cylinders have a tendency to shape like a bell as they wear.

If all is good, take off the muffler. Use about 7-8 2”-3” logs all around it and light them on fire. Should be enough wood to burn for a good 45 minutes or so. Let it go. You’ll see the muffler become a smoke cannon and if you’re lucky, it will blow about 8-12” flames out of both ends. Eventually it will quit smoking and just let it cool on the concrete in the driveway. Put it back in, rev it a few good times and it will blow out a bunch of soot. Then will be fine. I’ve had to do this to a few carts after rebuilding the engine. When they smoke for a long time before rebuild they accumulate a bunch of unburnt oil and stuff in there. The fire pit clears that all out.

[jwalsh965]

It was smoking bad before, so big fire in the plans.
Thanks

[CP241]

It’s kinda fun watching the oil burn out of it. It takes a good half hour to 45 minutes but works great. BBQ’ing the muffler is a fairly common practice for 2 strokes. Generally not necessary for 4 strokes under normal operating conditions. But when you have a motor that smokes and burns oil for a long time, it builds up. This should clean it out nicely.

[jwalsh965]

Bonfire is on top of the list.

[slonomo]

I've done this, it's pretty cool and works. Hopefully that solves your issue.

[sho305]

Or you can drive it hard until it stops smoking. Just check the oil in engine. They usually burn oil because of the rings.

[raydhd]

It didn't take very long on my HEAVILY smoking before rebuild G 14 with some running after the rebuild. 4 stroke exhaust runs a whole lot hotter than a 2 stroke unit.

[jwalsh965]

Removed muffler, and still smoking, must be stuck oil ring.

[CP241]

Originally Posted by jwalsh965

Removed muffler, and still smoking, must be stuck oil ring.

Never hurts to try :)

So back to my original response, did you check the cylinder for being shaped like a bell before you rebuilt it? If you don’t have the right tool you can use a ring and check the end gap in a few places. About an inch down, another inch further, etc. it should not vary at all. Any more than a couple thou and I’d have a machine shop inspect it.