Merc 115 problems

Hello to everyone!

I have been around boats all of my life, but finally just bought one of my own.
It is a 1990 SeaRay 16" with a Mercury 115 4 cylinder.
I knew it had engine issues, but figured I could deal with it, since the price was pretty good.

When I bought the boat, the engine would run but would die as soon as put into gear (in the water). I found out that #2 piston was burned up.
OK.....so it looks like I need to bore out cylinder #2 and replace the piston. The rest of the engine looks ok. I need to find out why this happened, and make sure it doesn't happen again. I didnt find any obvious problems like dirt in the carb, a failed reed valve, ect.....
Am I missing anything? I have been into pretty many four stroke engines, but this two stroke thing is new to me.

Also upon removing the power head, it seems that the drive shaft is kind of tight when I try to turn it by hand, when it is in gear. is this normal? Could this be related to the problem with the engine?

Thanks for any and all help!!!
Eric

Re: Merc 115 problems

I could see a piston getting burned if it's carb went lean at high rpm.

So it's hard to turn only when in gear? It's has to be propshaft bearings because the only difference when in gear is the propshaft is engaged. When in neutral is the prop hard to turn? You should drain and inspect the lower unit oil.

Re: Merc 115 problems

Thaks, Dave!
Yes it is hard to turn when in gear forward and reverse. it spins freely when in neutral.
I just think its strange that the engine would have two seperate problems at the same time.
Would a tight bearing cause the engine to strain and detonate?

like a car pulling a steep hill, when the engine pings?

Re: Merc 115 problems

Keep in mind weather in forward, reverse, neutral, you will have resistance because you are turning the water pump impeller. Buz

Re: Merc 115 problems

Eric Schultz said:

Thaks, Dave!
Yes it is hard to turn when in gear forward and reverse. it spins freely when in neutral.

Click to expand...

You said the driveshaft was hard to turn when in gear. I asked if the prop or propshaft was hard to turn in neutral.

Re: Merc 115 problems

The vertical shaft that is driven by the engine turns with resistance, and makes a squeking noise (like rubbing rubber) Maybe the pump as earlier mentioned. It does this in forward, neutral, and reverse. the prop turns freely when in neutral.

Re: Merc 115 problems

If your prop turns freely when in N your probably OK. As suggested before, change the lower unit lube and see if its milky or hase metal in it. If it hasn't been run in awhile you for sure need to replace the impeller. While you have the LU off and impeller out you should be able to tell if everything is working OK.