1991 Merc 115 Compression Numbers - 117 125 125 125 - Good or Bad???

[mrecho76]

Hi all,

So I recently got an 18ft Center Console that has a 1991 Merc 115 on it. It's been sitting for years and I don't know if it runs. Turned the prop in gear and the pistons seem to move fine. Injected a small amount of oil in the cylinders, moved the pistons around, and performed a compression test. The top cylinder is at 117psi and the other three are at 125psi. I know the main thing to hope for is similar numbers throughout. So my question is, are these numbers good or bad? Does this mean the top cylinder is shot?

If the numbers are ok, then I'm willing to put in the time and effort to do/rebuild carbs, fuel pump, impeller, fuel filter, plugs, thermostats, etc. But if these number indicate a bad powerhead or one that's about to go, I might look for another motor.

What are your thoughts?

Thanks!

 

[ondarvr]

It's fine

 

[Texasmark]

Go to the site archives or just Google search for the term "DeCarb". Do it and then keep Sea Foam in your fuel supply. Gonna bet the lower reading is due to sticking rings from sitting. The rings in that engine have to move to expand and establish a seal.....part of the Loop Charging system requirements. If there is excessive carbon or old combustion oil that has turned to grease over the years you need to dissolve that mess and blow it out......Decarb with Sea Foam does just that and keeping it in your fuel keeps it from happening again. I ran it in every tank of gas.