90 HP merc...no compression

[sduck]

Hello all...I have a 90 hp, 2 stroke, 2005 mercury outboard.
Up til no this motor has performed flawlessly. Went duck hunting last weekend (20 deg F). While running down the river the motor died as if it had run out of fuel. Restart fine. Ended up idling back and motor began to run on 2 cylinders.

Suspecting fuel pump i bought kit and installed. Did notice some water in fuel so pumped tank out (Inboard 18 gal in Lund Alaskan). Figured that would do it.

Next time out, same thing. Checked spark, good. Checked compression, BAD!!

90 - 0 - 90 from top to bottom. I realize this is overhaul time but what could cause this.
and what is the best repair manual to get? Got to do this myself.

Thanks

 

[Texasmark]

Re: 90 HP merc...no compression

I have an '02 version of that engine and an OEM service manual. The manual has no troubleshooting section for engine block problems; i.e. compression problems. The manual is 1.5 inches thick and covers 3 and 4 cylinder mid engines, but is not all that comprehensive; says a lot, but leaves a lot to be desired....my opinion. Like I can't even verify that this block is built in conventional Merc fashion where there is no head gasket and separate head component. Seems that it is integral to the block (like earlier designs) and the only things covering the top of the cylinder is the water jacket cover and sealing gasket.

So to suggest that you blew a head gasket is a misnomer, as there isn't one.

For you to loose that much compression one would think that the culprit would be obvious. But with the engine running on 2 cylinders and I assume no banging and clanking, that you didn't throw a rod. To break two rings simultaneously seems abnormal.

Only thing I can think of is that possibly the carb linkage came undone and that the #2 carb isn't getting any air, like the butterfly isn't opening. Logic tells me that if you can't suck up any air on the intake part of the stroke, you have nothing to compress hence no compression. Other than that man, I am at a loss for words.

HTH

Mark

 

[sduck]

Re: 90 HP merc...no compression

Justs to be sure i went and spun the motor over with the flywheel and piston moves as it should...carb linkage is good.

I can't help but think the water in fuel has something to do with this.

Also shouldn't there be an alarm of some sort on this motor?

Steve

 

[j_martin]

Re: 90 HP merc...no compression

Justs to be sure i went and spun the motor over with the flywheel and piston moves as it should...carb linkage is good.

I can't help but think the water in fuel has something to do with this.

Also shouldn't there be an alarm of some sort on this motor?

Steve

If the piston is moving, and there's no compression, then there is major engine damage to that piston or cylinder wall or both. There is no gasket above the ports, so it's bad metal.

Sorry.
John

 

[sduck]

Re: 90 HP merc...no compression

I will post more when i get the motor tore down as to what i find but...

Is it likely that i bunt a piston and can water in fuel cause this

Steve

 

[j_martin]

Re: 90 HP merc...no compression

I will post more when i get the motor tore down as to what i find but...

Is it likely that i bunt a piston and can water in fuel cause this

Steve

Usually when a single cylinder goes kerput like that, it turns out to be a fuel starvation issue. Not totally cut off, but running lean and hot.

With a little luck it won't be scored too bad, and one new piston and rings and a little acid clean up on the cylinder wall will fix it. (I'm assuming it's a plated cylinder.)

Of course you'll try to figure out what happened before you try to run it again. I'd tear down #2 carb and look for contamination, especially in the main jet.

hope it helps
john

 

[rodbolt]

Re: 90 HP merc...no compression

yes water or debris in a carbed motor like yours can and will smoke a piston rapidly.
usually in a cooling system failure the top piston smokes first.
best I recall your cyl liners are cast and boreable.
weak fuel pump can also cause it as can a ruptured fuel pump diaphram.

 

[sduck]

Re: 90 HP merc...no compression

I appreciate all the advice guys...

I have a merc service manual but is there another manual that might be better.

Also, do you have any recommendations on fuel/water filters and there application on an outboard.

 

[Faztbullet]

Re: 90 HP merc...no compression

I would check the other cylinders to see if it looks like they ran lean or are scuffed from lack of oil. In this temp(20F) the oil in oil tank may have thicked due to outside temp and towing(colder) to the point the oil mixture was lean or carbs may have iced and narrowed the venturis resulting in lean mixture or ingestion of water.I have seen carbs ice shut on a 40hp Mariner back in 1985, also check all the carbs for debris.

 

[kend301]

Re: 90 HP merc...no compression

Pull the plug , take a led light like you would find on a key chain , look in the cylinder as best as you can , make sure the piston is down while doing this ... Cheap mans borascope !

 

[sduck]

Re: 90 HP merc...no compression

So...as to the oil injection, should i not assume that it works properly in cold weather.
My dealer told me it would, as this was a concern of mine. Told me to just make sure and let the motor warm up first. Would i be better to mix oil in cold weather?