Engine Ran Loud then Quit

[mroyten]

I have 2 stroke 20hp 91 Merc and lately it had been running louder/rougher than usual but still performing as well as it had. Til today I was out running it and it died on me. Couldn't get it started again. Any ideas for me to start trouble shooting?

[boatfixer]

I'd check compression first, then check for spark.

Can you describe "louder". Overall exhaust loud or engine making a mechanical noise?

Any chance un-mixed gas was run through it?

[mroyten]

The louder sound was a rapid mechanical sound.

I have spark, check. And I'm pretty darn sure that I've been putting the proper amount of oil in the gas.

[boatfixer]

Did you do a compression test?

If you do find low compression, keep in mind there is no cylinder head on mercs, meaning to look inside the cylinders, you will have to remove the exhaust plates.

Have you had a good continious stream of water? Any reason to suspect it overheated?

[Sonicrunch]

Ah, the death rattle.

Does it turn over easy or hard?

[mroyten]

Did you do a compression test?

If you do find low compression, keep in mind there is no cylinder head on mercs, meaning to look inside the cylinders, you will have to remove the exhaust plates.

Have you had a good continious stream of water? Any reason to suspect it overheated?

Still need to do a compression test... I don't suspect overheating though, spark plugs looked fine, there was a consistent stream of water coming out and no visible signs of heat damage on the engine.

[delcecchi]

Isn't the poor man's compression test to pull on the cord? Does it feel the same as it did? Does it make noise? etc.

[mroyten]

I began to think back to when I first remember hearing the noise... I was out in the boat with my father in-law and he was driving and there was a lot of floating weeds. Well we had gone a fair distance and I look back and water was splashing up over the transom a bit and there was a bunch of weeds we had been dragging by the lower unit. Think something might have gone wrong from this instance?

I need to pick up a compression tester, thought my buddy would have one but doesn't. And yes when I pull the cord, it does feel different, like there is more suction...

[Surface Tension]

Having weeds around the lower unit is going to restrict the water from entering and the outboard will overheat.

Not only is the engine cooled by that water but the exhaust is as well.

I've seen it more then once where the engine and exhaust got hot enough to melt the aluminum plate and tube that directs the water and exhaust from engine to lower unit. After the initial overheating episode the next sign that this happened is the engine is louder. That is if the engine didn't get completely cooked when it overheated. Sometimes there is enough water to cool the engine that while it may have taken damage it'll still run.

[mroyten]

Okay, for this compression tester ordeal, what is the process that I should follow? Hook it up and pull the cord to get the reading?

[marine_man]

That's correct.. pull all the spark plug, turn it over a couple of times and read it.

Valv has a good post on it here:

How to Check Compression

marine_man

[mroyten]

Update on this post... a Sour one as compression test results in zero compression for one cylinder and 65lbs from the other. Is this the end of the line for my engine? What steps should I take next if it is salvageable?

[mroyten]

The cylinder with no compression - does have its piston moving so they guy who I had look at it mentioned that it most likely is the rings of the piston.

[Sonicrunch]

Even if the rings are wasted, you would still have a little compression. I would guess a hole in the piston. Either way, that motror has to come apart now.

If the cylinder walls are good, you can prolly do a successful rebuild.