Usually you do a compression check or a cylinder leak down test.

I watched my mechanic do mine..

He dropped the lower unit.. Connected water hose from faucet to uptake tube (hose clamp) to pressurize the block.. After just a bit water started to seep thru the head right at water jacket near top spark plug hole.. Starboard side..

Said it wasn't the first one he'd seen.. And told me what the problem was before he did it..

A compression test and a leak down test will tell you everything you need to know.

My SHO passed both of these tests with flying colors, and was still burning a ton of oil. 2 different mechanics couldn’t identify exact problem and recommended replacing power head.

I did this test first all was good within like 5%

So what was the problem?
A leak down test is performed under pressure. If it lets oil in, a leak down will show the problem. I guess they may not have done it properly. Did they run the engine to full operating temperature immediately before the test?

Was it valvestem seals?

I actually did this test just a little while ago before I read this. I found the leak on the starboard side.

Don’t know. Was told I would likely spend more money on labor if they completely tore apart and diagnosed issue by both shops. So paid for a new powerhead.

Thanks for the help everyone that posted here. I’m planning repowering my boat as soon as I can get a new engine.
But dang, it sure sucks that Yamaha knew these heads were weak and shipped who knows how many to the US. I would definitely put a mercury on there if it wasn’t even more expensive.

At the cost of a complete repower, ya might as well get that V8!!

I agree with Steez, if you're going to spend that kinda money get what you want and feel good about your investment. Sorry about your bad luck.

i had to make the same decision to spend the extra money sure am glad i did go with the v8

That's a good lookin ride right there!

Skeeter looks damn good with that Merc hanging off the back.

Hell yes it is! Bad to the bone.