I’m stumped as to why
 

I had my Yamaha 30 For sale and have taken it down due to the following

About 8months ago I ran a compression test and all 3 cylinders were right at 125.

Today I set it up on a stand and ran another test and 2 were at 125 and 1 at 70

I did notice that when I hit the key it seems to not want to turn over but it eventually did turn over. But besides that it sounded fine.

What could be the cause of this?

I think I'm going to take the head off check on the gasket and look at the cylinder wall and piston. Hopefully its the gasket

So I took off the head today and found that the lowest piston is shot. Nearest I can think is that the engine sat for awhile had a stuck ring and when I cranked it up it sounded like it was stuck but let loose and here are the results. You can see where a small part came off the piston at around the 3 o'clock position and then damaged the piston around the 12 o'clock position. The cylinder wall amazingly did not get damaged. I also found plenty if deposits in the cooling system especially down low.

Options are

Sell for parts
Have someone rebuild it.
Or have fun and do it myself.... although I've never done this before.

I mean what's the worse that can happen

Pulling a power head off and rebuilding it is doable. If you have the tools and time it can be done. I’m a big time gear head. Rebuilding an outboard isn’t complicated but corrosion is such a pain.

That said, is it really worth it? I’d tally up parts cost vs buying something used.

I rebuilt our boat's 1973 115 Evinrude when I was around 14-15 years old, just followed the service manual's instructions and, of course, had my father's and cousin's supervision. It started right away and ran flawlessly for another year until we sold the boat. I suggest you have fun and rebuild it!

Artificial reef…..

As Moose says....don't share the numbers!! :)

Bottom cylinder, sounds familiar because my 90 Yamaha did the same thing with water seeping in due to corrosion at the top of the cylinder. I had a new short block installed. The cylinder's metal can not be welded and machined because the contraction and expansion will not let the weld hold. Another one of thousands of Yamaha corrosion stories.

I don’t expect that I will be able to fix the engine taking into consideration my mechanic skills and having someone do it is not cost effective…but I have it setup in the gara=ge and in my spare time I plan to take it apart and see what it looks like inside. Maybe sell some parts???

I recently replaced the head gasket and water jacket gaskets on my Tohatsu 90. I applied oil, heat, tapped the bolts and still broke 22 bolts. It cost me $700 for a guy to drill them out. Corrosion is THE buzz kill when working on old outboards.

So I started tearing apart the rest of the engine. Apparently it's worse than what I thought. I didn't notice this till now.

So unless I run across a very cheap power head...is a parts motor. I already took apart most of it and bagged all the parts