20 lbs compression in PTO cyl

[olds72]

OK, you all know I was having problems with my plugs fouling after about an hour of riding. Two weeks ago It did the same thing and I made some adjustments to the oil pump, It set way to rich. I cut back my spark plug wires. Then my ski wouldn't start. So I check the spark and it was good. I was getting fuel. So the next step was to check compression. I did that today. What I found was the mag side at 130 lbs and the pto at 20 lbs. I pulled the head and this is what I found. This motor has only 4 hrs on the rebuild. What went wrong?
Pic 1 is the PTO piston notice the top had indents or nicks. Pic 2 is the mag side cylinder wall, it has score marks(odd). Pic 3 is the pto side cylinder head. It also has little nicks., but is not black from carbon. Pic 4 is the mag side of the cylinder head. It has one indent in it, but otherwise it's just black. What do you recommend?

 

[Dr Honda]

Did you do a full rebuild, or just a top end? (i don't remember)

If you did just a top end, then I would say that something was still down in the crank, and it came up, and beat the PTO jug.

If it was a full rebuild... I'm not sure what to say. The damage is mechanical, not a lean run. The only thing that comes to mind is that one of the rings got damaged during the install, and it failed.

Is there any melted spots on the piston?

 

[olds72]

Did you do a full rebuild, or just a top end? (i don't remember)

If you did just a top end, then I would say that something was still down in the crank, and it came up, and beat the PTO jug.

If it was a full rebuild... I'm not sure what to say. The damage is mechanical, not a lean run. The only thing that comes to mind is that one of the rings got damaged during the install, and it failed.

Is there any melted spots on the piston?

This was a full rebuild, although I did buy a used crank. Your right on when you say one of the rings came apart. I pulled the PTO jug and the bottom ring is gone. I'm not sure why? I'm positive I installed the rings correctly. The mag cylinder is still there. I guess I'll pull the complete engine and split the cases. I need to find the ring/pieces. The rod still feels good on the crank. Although I won't know for sure until I get it apart.
When I pulled the engine apart the first time (I bought it with a bad engine) the PTO rod was loose on the crank.

 

[Bills86e]

combustion chamber damage

You can fix the symptoms, but you need to cure the cause. Read up on posts
similiar, and your manual. Had the ski injested water, ran fuel lean, or oil failure
? Let us know after ya get the jugs off! Closely inspect the injector gaskets for
an air leak. A bad sensor will tell mpem to go into limp mode, run on just one cylinder.
Pull fuel pump and inspect/test pressure clean fuel sock. Bills86e

 

[olds72]

You can fix the symptoms, but you need to cure the cause. Read up on posts
similiar, and your manual. Had the ski injested water, ran fuel lean, or oil failure
? Let us know after ya get the jugs off! Closely inspect the injector gaskets for
an air leak. A bad sensor will tell mpem to go into limp mode, run on just one cylinder.
Pull fuel pump and inspect/test pressure clean fuel sock. Bills86e

No water injested. fuel pump puts out plenty of fuel. Although I never checked the pressure. I unplugged the fuel line from the rail and cranked the engine over and I got lots of fuel. I had the oil pump set rich and its a brand new OEM pump ($200). One thing I noticed when I remove the air box that it was not all the way sealed at the bottom. I pulled the pump and cleaned the sock & tank before I first fired it up.