I have 1985 Yamaha 90 it has 3 hours on a overhauled powerhead. Saturday I had it out and it ran fine until suddenly I felt a loss in power and the power head started making a knocking noise. I got it home and did a compression check and all three cylinders looked good 116. I couldn't figure it out it sounded like it was coming from the top part of the engine. So I removed the spark plugs and using a small flash light I found the top piston looked like it had metal shavings on it but the spark plug looked ok. I removed the head and found the top piston and head was beat up almost like something like a nut or some thing had gotten in and got pulverized. What do you guys think could have caused this? Like I said previously it only had 3 hours on an overhaul. I'd been running 8oz of oil per 6 gallons of gas plus whatever the injection system was giving it. I installed a new oil, fuel and water pump plus had the carb rebuilt. I know the injection system was working because I marked and measured the oil after every run. I had it overhauled by TMS, boatpartstore.com. Has anyone had any dealings with them? I called them today and they told me to send the powehead back to them but made it sound like it was my fault.<br />I was very careful to follow the break-in procedures and double checked everything while installing the powerhead and components.<br />What makes me wonder is that when I got the powerhead back and installed I found they had installed the head gasket backwards.
