Looking for advice on a GX160

[jjdlc]

Thought someone here might could help me out. I'm a chainsaw guy, don't have a lot of experience with 4 strokes, but sometimes find myself working on one. This is a new one on me, and I'm just hoping someone might can point me in the right direction. This is from a Honda GX160 on a log splitter a buddy asked me to look at. The motor started easy, and ran, but smoked badly, grayish white smoke, but smelled strongly like oil burning. I did a compression test, and it was a bit low, so I figured it was probably in need of rings, and maybe needed to be bored.

Tore it down, and was surprised that the cylinder was in pretty good shape, not near as much wear as I expected, and the rings didn't really appear to be worn enough to account for the amount of smoke the motor was putting out. I took a closer look at the head, and the exhaust valve and port were caked in carbon. I pulled the valve, and took a wire brush to it to see what was underneath. The pictures show what I found, and am unclear what I'm looking at. What I thought was pure carbon build up looks to be metal buildup instead. Is it extruded from the valve itself? Was the motor running hot? Lean condition? The valve seat has a nice groove in it rather than the bevel I expected, the edge of the valve feels the same. The inside of the exhaust port is pretty caked in carbon too.



At this point, I'm thinking a whole new head is probably in order, Im not sure the current head is worth salvaging, as I'm afraid putting new parts in it may just be throwing good money at bad. I'll probably re-ring it too, maybe a new piston and con-rod too. Anyway, hope someone can help me out and tell me if I'm off in left field.

 

[Conquistador3]

Try scrubbing the carbon and putting it back together. Carbon buildup is the first cause of low compression/blue smoke on small four stroke engines.

Also remember that Honda GX engines have an inbuilt decompression valve which is totally unlike any used on two stroke engines (for obvious reasons... ) . If I remember correctly it's a speed sensitive groove/notch/whatever in the camshaft. That makes checking compression not exactly easy if pulling the starter by hand.

Finally check for black soot inside the rocker area behind the exhaust valve: that's usually a sign the valve guides are starting to wear out even if there's no radial play. But unless the engine was tuned and raced (Honda GX160/200 are very common kart engines) the seats on these Honda engines are good for hundreds of hours.