Low compression on top cylinder.

[WeezyMelt]

Have a 97 Yamaha 80hp 2 stroke outboard that I purchased used. At the time of purchase all cylinders read 115 compression. First outing it ran great but on the second outing I noticed a loss in power. Took it to a mechanic and he said the top spark plug had water on it and the compression was now reading 60 while the other two were still 115. He said it would need a rebuild and quoted me at 5/6k. Decided to take it home and work on it myself or buy another outboard.
Opened it up and noticed the head gasket looked like it was toast but I also have no idea what I am doing or looking at… lol.

Would a new gasket fix the compression on the top cylinder? I didn’t feel any scoring on the cylinder wall and I found a replacement for 50 bucks online. Figured it would be worth a shot before buying a replacement. Just curious if there is anything else I should be looking at? Or if there are other issues I am missing due to lack of knowledge. Thank you!

 

[racerone]

It is a shame that a mechanic / shop would quote for a rebuild without checking for blown head gasket.-----The head is warped.-----So refinish it and install a new head gasket.---Go boating.-----It might not hurt to tell the mechanic what you found.-----Might not treat you the same way next time.

 

[WeezyMelt]

It is a shame that a mechanic / shop would quote for a rebuild without checking for blown head gasket.-----The head is warped.-----So refinish it and install a new head gasket.---Go boating.-----It might not hurt to tell the mechanic what you found.-----Might not treat you the same way next time.

Yeah he happens to be 1 of 2 mechanics in my small town and is apparently always 1 week to a month behind on repairs so I think he just didn’t want the job.
Sorry not much of a mechanic, when you say the head is warped and to refinish it, do you mean the area where the gasket sits needs to be evened out?

 

[racerone]

All aluminum cylinder heads warp with time.-----A flat surface of glass / table saw can be used with emery cloth to true it up.-----Or valve grinding compound as well.----Never seen one that was not warped to some degree.

 

[99yam40]

Yeah he happens to be 1 of 2 mechanics in my small town and is apparently always 1 week to a month behind on repairs so I think he just didn’t want the job.
Sorry not much of a mechanic, when you say the head is warped and to refinish it, do you mean the area where the gasket sits needs to be evened out?

no, the whole head needs to resurfaced until flat

 

[99yam40]

no, the whole head needs to resurfaced until flat

I have done small heads myself at home before, but something the size you are dealing with may be best to take it to a shop to have it resurfaced.