Ok...My newest problem on my boat:

I was on the lake the other day with my kids and once I got on plane, about 60 seconds later the motor died. It started back up easily but only had about half of it power. wouldn't even try getting on plane.

I took it back home and pulled the plugs and noticed the first three were pretty oily, but the last one I pulled was covered in a hard gray substance. I assume this is carbon build up, right?

I pulled off the head in front of the piston and the piston was completely covered in the same stuff. Piston was also pretty loose.

Any advice would be appreciated.
What would cause the carbon build up on this one piston? Could it have been from worn out rings?

I took a few pictures of the piston, and I'll try to post them in a few hours.


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Two stroke correct? I think what you have is no fuel delivery to this cylinder. No fuel to a cylinder has the same results as running straight gas in a two stroker. Because it is only one cylinder, more than likely the cause is from a fouled carb or plugged jet and not the VRO. If you had to choke it a lot this spring to get it to 'run right' than that even points more to a carb problem. The residue that you are seeing is probably melted metal shavings.

Black and oily residue on plugs in a two stroke is a sign of incomplete combustion. Ideally the plugs should be dry and generally covered with mostly a light to medium brown 'fluffy hot chocolate' residue at the electrode and fading to the edge of the plug. However if you idle a lot before pulling the plugs, you won't see this.

what motor and HP?

'92 Johnson 115 V4 Two-Stroke

Just bought the boat a few months ago... It had old gas in it that had sat for over a year probably. I cleaned everything out in the fuel system (carbs too). But this doesn't look like something I've done to it in the few times I've run it. It looks more like it's happened over a longer period of time.

First boat... So I'm not exactly sure about it all.

Cast Net... I did have to choke it to start it most of the time. But idled fine once it started.

I'll post pics as soon as I can.

Thanks

The gray substance is aluminum, transfered from the melting piston.

What happened is probably just as cast net said. After sitting around for a year, oil & gas residue in the carbs hardened into varnish, restricting fuel flow and resulting in a lean condition (too much air, too little fuel, too little oil). Lean condition means high combustion temperature.

Meanwhile, the neoprene rubber vanes on the water pump impeller take on a permanent "curve" from being held in one position for a year, reducing its ability to provide water pressure.

What to do: with any luck, the cylinder can be honed or if not, maybe it can be sleeved.

If you're a do-it-yourselfer, get yourself a factory service manual ( http://www.marineengine.com or http://www.kencook.com ) and roll up your sleeves. there's some guys over on http://forums.iboats.com/forumdisplay.php?f=24 that can walk you through it.

Otherwise, take it to a trusted mechanic.

Sorry to hear about your troubles. Good luck.

Not starting, when you are running it. A lot of boaters will take their boat out in the spring and once on the lake will continually choke it to get it to run right. When that happens it is a sign of a carb problem.

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Yup, that is metal from a different part of the engine where metal wasn't when the engine was built.

So it's not metal from the piston? where's it from?

This sounds like its getting worse and worse?

Rings, cylinder, piston, crankshaft rod bearing, wrist pin, etc. Won't really know until it is torn down and inspected. Worst case there will be damage to the crank, best case new piston rings, rod, and a sleeve in the cylinder or honing.

That looks awful familiar. I have the same motor but a '93 model. Same thing. Bottom cylinder too and looks to be the same hole. Mine is just at the ports though. Did you feel any ridges on the cylinder wall? I'm still debating what I am going to do to mine. Probably try to hone then replace piston and rings. But I would sure like to know what caused it too.

Cylinder wall feels pretty smooth. Just like the top cylinder.

So will I HAVE to do something to the Cylinder? Or can I just replace the Piston and rings.
Back when I replaced the top end in my Dirt bike... thats all I had to do.

Anybody know about how much I'm lookin at spending for all this?

Sorry for all the probably obvious Questions... But like I said this is my first boat.

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That big score on the cylinder wall is enough to tell me she's done. Time for a rebuild. That piston got really hot. Have it torn down, send the block off to a machine shop, and let them tell you what they can do with it. That would be the first place to start. Don't buy any parts, until the machine shop says so. They will be able to tell you what you need as far as size goes.

Yep, that one got hot. could be from not enough oil (as said before). or the water pump not working properly.

you've been given the perfect advise. take it to a mechanic, etc.

i had to do mine sometime ago, but it wasn't that bad. I used jay smith racing, since my engine is a high performance engine.
cost me 3200.00.

i would say your's will be more like 4500 or possibly more. new pistons,rings, sleeves, etc.

that's trully a bummer.

good luck

It's only a 3 to 4 thousand dollar boat.... Just bought it a few months ago, So I could take my kids to the lake this summer. What a huge disappointment.

Thanks for your help though guys.

Like Bristow said....see if a machine shop will give an estimate on it. For $3K you can probably buy another engine, but you wont know how well it's been maintained. That's a fairly common engine, so you may want to look for a used powerhead that's sitting on a trashed lower unit and maybe pick it up cheap.

Do NOT, however, simply buy a new piston and rings and install them without dealing with that cylinder, bearings, etc.

While I had it torn down, I'd go thru it completely, if I were you. ( if the cost wasnt too high)

Invest in a new used motor, you can usually find them for less than the cost of rebuild. If you can rig it your self or buy the same model / style motor you might come up ok.

good luck.

In the third pick the small line is pinched off some...Maybe the reason for it gettin hot....

That line is only a water diverter hose Spanky. I see signs of head gasket leaking on the bad cylinder most likly caused by week water pressure or thermostat. As you can see the top cylinder was about to do the same thing.

Is that Splitfire Sparkplugs? UCK! It definatly has a water mark in the bottom hole. Could have come from the exhaust, A mist of water on the top of a hot piston,,,,,,,,,POOF! no piston at all............

these are Champion plugs. Not sure what exactly caused it yet. But I'm going to tear it down Friday, And see what I can find.

The Gaskets seemed to have a good seal, but I'm no expert.

The pictures make the cylinder wall look worse than it is. Like I said, I'm no expert...But would it be possible... If there was no other damage other than the piston... To just replace the piston, rings, and rod?
After I pull it all off and have the piston out I'll consult a mechanic first, to inspect the cylinder before just sticking in a new piston, of course.

What do ya'll think?

by the way I'm not trying to be stubborn... I just don't have 3 grand to put into a motor I just bought 2 months ago. So I'm weighing ALL options.

Thanks again for all the help so far.

Best thing to do and probably what I am going to do to mine is Strip it down and take to a machine shop to check the bottom cylinder to see if your going to get by with just a good hone or if you can bore it out or if you'll need to resleeve. I'd probably have them check rods and crank for warpage or any other damage. You'll need to (or should) rering the other holes while your there so hone the other cylinders out to. New bearings of course. Don't forget new thermostat or at least rebuild it.

Ya let a machine shop tell you. Or if you happen to be a member of a forum with experts, maybe one of 'em will take a first hand look at it & then you'll know. If it's scored too badly, it won't hold compression, won't never run very well if at all, then you'll have wasted a lot of resources.

You've got to figure out best you can what caused it, else it'll happen again after it's fixed. Drop the lower & see what the water pump looks like, pull the carbs & examine the jets closely. I'm sure there's more possibilities I haven't thought of.

How old are the kids? Rebuilding an outboard can be an opportunity for a priceless bonding experience.

If your fingernail digs into the grove on the cylinder wall of the down piston, you're going to have to have it bored. Re-honing it isn't going to remove the cylinder wall damage alone.

Don't just do one piston either. If you're going to rebuild it, spend the extra money and do it right.

The reason why? If you put one fresh piston in that hole, the other ones are just as tired as the one that dropped. They won't be able to keep up with that one fresh one for very long. Generally within 5-8 months, one of the other ones will drop, and then you're back to square one. Another tear down, back to the machine shop, ect.

Just do it right from the beginning.

As far as a new engine vs. a rebuild. If the costs are the same, rebuild. That way you know what you got.

Thanks... Lots of good info.

JTexas... The kids are 7 and 5 year old girls, and a one year old son. A little young to be interested in rebuilding a motor... But Hopefully I can get it running again before they lose interest in the new boat.

Thanks