melted or burned up piston?

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dragula65000

Petty Officer 2nd Class

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Apr 14, 2004

Messages

180

• Dec 31, 2005

• #1

Well, I think I finally cooked my motor. I was goin down the river about quarter throttle, then punched it. The boat planed out good at about 2500 rpm, then it felt like I dropped a cylinder, throttled back, and it shut off. No more start. Sat around for a while, switched out 2 other batts, and no start. Got home, and had spark on one cylinder. The next day, I pulled the plugs, and eventually pulled the head, and the exhaust side of the piston was melted, nice and clean, and had melted piston in the exhaust ports, and bonded to the cylinder wall. I dont know how to add a pic, so it would be appreciated if someone can help me.

 

M

mikeyzx2

Chief Petty Officer

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May 1, 2005

Messages

633

• Dec 31, 2005

• #2

Re: melted or burned up piston?

You can have photos hosted by imageshack, or photobucket. Upload them there, then you can paste the links here.

 

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dragula65000

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180

• Dec 31, 2005

• #3

Re: melted or burned up piston?

here are the pics

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dragula65000

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180

• Dec 31, 2005

• #4

Re: melted or burned up piston?

 

D

dragula65000

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• Dec 31, 2005

• #5

Re: melted or burned up piston?

 

D

dragula65000

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• Dec 31, 2005

• #6

Re: melted or burned up piston?

WEll, here it is. Also, when I got back and checked the spark, this is the only cylinder that had spark. Did the stator go screwy? I know I have to do a rebuild now. Yeppie. Cant wait. Im just trying to find out waht may have happened, is detonation, and if the motor can be resleeved. 1989 johnson 175 gt crossflow v-6.

 

R

R.Johnson

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Sep 24, 2003

Messages

4,446

• Jan 1, 2006

• #7

Re: melted or burned up piston?

Before you take anything apart, find TDC on each cylinder, and mark the flywheel at TDC for each cylinder. Then check the timing on each cylinder. Number each cylinder on the flywheel so you know where youare at.

 

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Dhadley

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Feb 4, 2001

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16,978

• Jan 1, 2006

• #8

Re: melted or burned up piston?

What spark plugs are you using?

 

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dragula65000

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180

• Jan 1, 2006

• #9

Re: melted or burned up piston?

The plugs are Champion, L77JC4. R.Johnson, I understand the marking and all, but each cylinder? When I put it all back together, wont I just do a sync & linc, and do the timing as it says in the book? Is it like timing a normal engine by finding TDC on #1 and going from there? How do I find TDC on 2 strokes? Is it just when the cylinder is at the top no matter what stroke?

 

R

R.Johnson

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4,446

• Jan 1, 2006

• #10

Re: melted or burned up piston?

I'm really at a loss as to why that piston is that melted. I was wondering if something really went haywire with the pak, such as double firing. When a two stroke is at TDC, that's it. They fire on every full stroke. I was hoping Dhadley would comment further on the photo's. Do I understand correctly, you now have ignition only on one cylinder?

 

D

Dhadley

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16,978

• Jan 1, 2006

• #11

Re: melted or burned up piston?

No need for me RJ. Youve got him going in the right direction. That damage is from some sort of abnormal ignition. The plugs are OK so the timing is the next obvious deal.<br /><br />One question Drag -- was anything, and I mean ANYTHING, changed / moved / adjusted / tweaked / removed / replaced between the last time it ran OK and the time this happened?<br /><br />OK, two questions -- how old is the fuel?

 

R

R.Johnson

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4,446

• Jan 1, 2006

• #12

Re: melted or burned up piston?

Take a look at the sensor magnet on the hub of the flywheel, and see if it is loose, or has slipped. That would show up in the test I mentioned above.

 

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emdsapmgr

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Dec 9, 2005

Messages

11,551

• Jan 1, 2006

• #13

Re: melted or burned up piston?

You might want to pull the carb that feeds that cylinder and look at the mid and high speed jet on that side. Possible that you have a restriction (debris) in the jet(s).

 

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dragula65000

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180

• Jan 2, 2006

• #14

Re: melted or burned up piston?

I showed the pics to a fellow boat guy, and the ONLY cylinder that is firing, is the one above. I put a new pack on last year, and the gas was no joke, fresh. Got it right before we went out. Now when I pulled the head, there was some water left in the cylinder. Was it just in the jacket, or blown gasket? The tell tale was the molten piston on the plug. Im thinking somehow the stator was sending too much juice to that cylinder, and the battery was cranking at 10.4 volts. Can this be a cause? When I rebuild, Im putting new ignition in anyway.

 

R

R.Johnson

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4,446

• Jan 2, 2006

• #15

Re: melted or burned up piston?

If you rebuild this engine, all carb's have to be done. That is standard procedure. It is hard to tell by the photo's, but you may be able to rebore this engine. To me, it look's like aluminum build-up on the cylinder wall, more than a gouge. All you can do is measure it, and see.

 

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dragula65000

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180

• Jan 2, 2006

• #16

Re: melted or burned up piston?

Yeah, it was just aluminum build up. I was able to peel it off a little bit, but I held off a bit. Can I rebuild with just replacing one piston and use the old ones? I wanna do this as cost efective as possible, but done right. Also, can this motor possibly be resleeved? If I change on piston, do I have to replace all of them? The motor still turns fine, but Im not trying to start it, due to the hole in the piston, and it missing, so Im sure it doesnt have anything in the lower end demolished. I know its a process, but is it real hard? How about the needle roller bearings? Hard, or just a pain? Thanks for all your input guys. It helps alot. Im just trying to figure out how this could have happened. All the prior problems Ive been having led me to the stator, and the rectifier, due to the motor draining a fully charged battery in 3 minutes.

 

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Dhadley

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Feb 4, 2001

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16,978

• Jan 2, 2006

• #17

Re: melted or burned up piston?

Once you get it apart the machine shop will measure the cylinders. That will tell us what has to be bored. You can replace 1 piston if the other cylinders measure in spec and the pistons are OK. I doubt youll have to resleeve that cylinder unless its cracked.

 

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dragula65000

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180

• Jan 2, 2006

• #18

Re: melted or burned up piston?

Good. I dont think its to bad. Im just wondering if I can resleeve it. Thats all. Thanks for the help and all the input guys. Ive been on here for a while, and everyone has helped me out. Hopefully, I should be good with the rebuild, but I'm sure ya'll be able to help.

 

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Dhadley

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16,978

• Jan 3, 2006

• #19

Re: melted or burned up piston?

Sure you can resleeve it but its a lot cheaper to just bore it. Personally I see nothing wrong with resleeving but I wouldnt do it unless I had to.

 

D

dragula65000

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180

• Jan 3, 2006

• #20

Re: melted or burned up piston?

Im gonna see if I can get away with just honing the cyliners. If so, can I still reuse the old pistons if they are in good condition? Just trying to keep the rebuild as cheap as possible.