Turns out my #2 piston was scored afterall on my 1999 25 HP merc. The mechanic took off the exhaust port and showed it to me. The choice was to keep it in the shop and spend $1000.00 to rebuild or do it myself for $300.00.<br />I have disasembled things and removed the carb, took the top bolt off the Flywheel but I can't get it off. There looks like a keychucked female part the bolt went into. I have tried banging it up with a rubber mallet and tried two prybars unsuccesfully. I need to get this off before removing the powerhead. <br />How much scoring is acceptable on the cyl wall? I can see the piston's shape but not the cyl wall<br />Does anyone have any tips for me.<br />Mercury 25EL<br />serial #0G765886
<br /><br />If the cylider is scored to the point that you cant lightly hone it out, you will have to get it bored, likely you will have to replace the piston. Did you figure out why it happened in the first place?