No Compression on Top Cylindetr

[wdjankowski]

I have a 1988 Merc 60HP 3 cyl (2 Stroke) that has zero compression on the top cylinder (125 for the other 2 cyls). With it being a 2 stroke, am I correct in stating that there would not be a reed valve issue, and it would have to be a piston or piston ring issue? Or on the compression stroke the reed valves do hold compression for part of the stroke?

 

[galamb]

You are correct, not a reed problem - cylinder, rings or piston is chewed.

If the reeds were bad your gas/air/oil would get blown back out through the carb(s) when the piston was on it's "down stroke" - taking the easier way out you would lose most of the mix out through the carb throat, instead of forcing it up into the intake (transfer) port. Once the piston has passed the intake/exhaust ports (on it's way to the top), the reeds will have zero effect on whatever is in the cylinder.

 

[papyson]

that particular engine likes a new top piston every few years.....

 

[fastjeff]

Right. Hopefully the block is salvageable. I run these motors and have saved at least 5 of them with burnt top pistons. Here's what one of the LEAST damaged pistons looked like.

Jeff