No compression. Pulled the head

[prairieboy]

So I have a solid 150 in the PTO side but 0 to very low that I reported a little bit ago.

I pulled the rave and it is fine. So I went ahead and pulled the head today. Piston is in one piece and the top ring is there. Can't say for sure if the bottom ring is. Engine turns with no troubles.

Only thing I could see was some carbon buildup and a little pitting on the Piston. The combustion chamber looks really good.

The worst part was some scoring mostly on the exhaust side. A little on the intake side as well. Hopefully these pictures will explain what my dilemma is and with your expert advice is if I should just order new jug and Piston and gaskets from sbt.

Could the carbon buildup from over time have caused the scoring in the walls which would lead to little or no compression?

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[Dr Honda]

That's not "Carbon Build up" as you are thinking. That's carbon from a lack of wash. So... that cyl was running extremely lean, and you had a light melt-down.

If you pull the jug... I'm guessing the rings are stuck from melted aluminum being over them.

 

[prairieboy]

Thanks Doc. So is the scoring causing me to have no compression?

I'm almost certain that it was running lean as the carbs, which have now been redone, we're quite gummed up.

What's the next step? Should I just replace with new from sbt?

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[Dr Honda]

Since you are in a cold weather part of the world... I would pull the jug... and look first.

If the rings are just stuck... I would free the rings, and give the piston skirt a light sanding. Then, hone the melted aluminum off the cyl wall, and slap it back together... and finish the season. I can't tell you how many times I've done that with a 2-stroke dirtbike, just to get though the weekend.


Then... once winter sets in... pull the engine for a proper rebuild.