Where to start... 96? Merc 40hp 2St 4cyl

[Slick Rick]

Well... I bought a project boat for which I already have a motor for, but the project boat came with a 40hp merc that was not in a running condition.

I planned on not doing anything to it, but the tinker'r in me has me messing with it.

Here are the symptoms:

Turn Key = Quick turn over sound immediately stopped by a clunk noise.

Remove engine cover and manually attempt to turn flywheel = movement from about 1 - 2 on a clock. Feels like I'm hitting something in both directions. It seems if I mess with it enough trying to turn it by hand back and fourth a bunch, the start and stop positions change and possible more or less movement (not much).

In forward, Neutral, or reverse... same thing.

Removed spark plugs, same thing. I can see a pistons moving slightly with flywheel movement, and plug colors look different from top to bottom, no fouling, but a little lean to the eye towards the bottom cylinder.

PO said that he was running, and motor just stopped and he got towed back in. I didn't get any other info as I didn't plan on doing anything with it. Motor has oil in it and PO said it hadn't run out at time of incident, but who knows.

Any idea where I should start? I'm looking for things to try before I assume 100% that the engine needs to be completely rebuilt. I'm not outboard expert, so maybe there is some linkage to look out for.

Thanks for the time,

Rick

 

[gwukena]

Re: Where to start... 96? Merc 40hp 2St 4cyl

Remove lower unit and try to turn over by hand again, if it turns free, lower unit is the problem, still doesn't want to turn, powerhead teardown time.

 

[Slick Rick]

Re: Where to start... 96? Merc 40hp 2St 4cyl

Remove lower unit and try to turn over by hand again, if it turns free, lower unit is the problem, still doesn't want to turn, powerhead teardown time.

Will do... I'll take it down this weekend and report back. Should be fun either way.
I've tore down many dirtbike, but this will be my first outboard!

-Rick

 

[Slick Rick]

Re: Where to start... 96? Merc 40hp 2St 4cyl

Okay... so I took the lower end off just now and everything is still the same.

Any other suggestions before attempting to remove the powerhead?

The clunk noise I hear seems to be coming from just below the powerhead but I'm not 100%.

 

[Slick Rick]

Re: Where to start... 96? Merc 40hp 2St 4cyl

Looks like I made a mistake when I stated all the pistons moved a little with the little flywheel movements I could make.

The #3 Cylinder piston is NOT moving, while 1,2,4 are. I'm not rocket scientist but that leads me to believe that the rod was busted.



Thanks for all the help. I'll completely tear it down over the winter for some much needed experience for future repairs.