Mercury 100 2+2 no oil on full throttle run

[58 Alumacraft]

My Mercury 100 died at full throttle, it felt like it seized. It started right back up and would run fine except for full throttle where it had a ticking noise and would stall. I opened the hood and noticed oil dripping from the oil pump area, took it into a Merc dealer and they found a cracked oil line. They replaced all oil lines and did a compression test and said it was in specs. I tested it myself in the garage and found top to bottom PSI readings of 125, 115, 130, 130. The ticking noise is gone and it seems to run good but I'm concerned about the way that it sounded when stalling as if it seized and the ticking noise that it made. I'm not sure how tough these engine are, would it be wise to tear it down for inspection or just run it?

 

[Faztbullet]

Pull the exhaust cover and inspect...#2 likely scuffed

 

[58 Alumacraft]

Good call Faztbullet, I took off the exhaust plate, there is scoring on #2 cylinder and a little on #1. Could someone give me the name of an outboard shop in SE MN that would be able to hone this once I get the power head off?

 

[Faztbullet]

https://www.billbune.com/services.html

 

[jimmbo]

You might have to go oversize on those two. In any case a deglazing of any unscored cylinders and new rings would be a good idea

 

[58 Alumacraft]

Here’s pics of the #2 damage. Thanks for the advice

 

[Faztbullet]

Most likely will need bored as cannot see bottom side of cylinder wall. Use the WSM rebuild kit as it has every thing you need. This is why I don't rely on compression test as it really only tells you that cylinder has pressure to support combustion and not what is condition of engine. Repaired many a blown motor with good compression.

 

[58 Alumacraft]

I have two options, bore .015 over or new sleeve. Boring is about $75 new sleeve $200+.........which one is the better way to go??

I'm not concerned about cost with this, just looking for the best most reliable repair possible.

 

[Faztbullet]

Bore as sleeve only need replaced if heavily damaged. Only use cast pistons...

 

[58 Alumacraft]

I finally got it back together, thanks again for the advice Faztbullet!
Bill Bune Enterprises bored #2 cylinder .015 over and deglazed honed the others.

I went with genuine Mercury parts which included:
.015" over piston assembly set
New needle bearings for piston pin
New connecting rod bearing cage kit (not necessary as rod was good)
Complete gasket kit (this included gaskets for pretty much the entire outboard)
New rings for the other three
Replaced the water pump impeller as long as I had it all apart

This was an expensive time consuming repair, make sure you check all oil lines for cracks or damage before using each season!