Scratched piston

[Mallett]

Working on the kg7 that I over heated trying to get the quince exhaust on. It still turns over so not seized. One of the piston’s rings move the other piston rings are stuck. I checked them through the opening on the side. After that I pulled the head and cylinders. The one on top is gouged enough that the rings don’t move. Can I find a piston? If I do can I just replace the piston and rings. Would a piston from a kf7 work? Do I have to take more of the motor apart?
thanks.

[PM T2]

That damage is likely caused either by some foreign body getting into the combustion chamber or severe overheating of the piston while running. The aluminum is actually swaged over the ring. I’m just fixing a similar problem that was caused by a reed valve breaking off and getting into the piston travel area. I got the rings out of the groove but it takes patience and time because you have to convince the aluminum that it wants to move enough to let the ring go free. I kept tapping t he opposite side of t he ring with a piece of hardwood until the ring started working its way through the aluminum obstruction.

All that being said, I’d suggest you split the crankcase and look at your reeds just to make sure. You can risk it, of course, and leave t he crankcase alone, that’s your call. I’m not that good on Merc part interchange but I believe you could swap a KF7 piston in there, and that you CAN do without splitting the crankcase. Hopefully somebody who knows merc part interchange better than I can interject if I’m off base.

Best
PM T2

He's livin' in his own private Idaho..... I hope to go out quietly in my sleep, like my grand-dad did..... and not screaming, like the passengers in his car...

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Mallett

[John Schubert]

The Hastings Co in MN makes all sizes of piston rings for Mercury & others. Yes a piston from a JF7, MK20 & MK25 can be used if all std. bore. You will have to separate the block from the crankcase then remove the piston from the connecting rod. There is no removal head, it’s just a water jacket cover

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Mallett

[green-thumbs]

Piston and Piston Pin assembly
Part # 718-1193 A2 for KE7, KF7 and KG7 per parts manual
Unless previously rebuilt it is likely the upper and lowerr crankshaft seals are crap,
Reed failure suggests rust or
too long service.
KE7 powerhead sits disassembled on my bench, I know ALL about getting one apart and am about to learn how to reassemble. First time
is the charm or the curse
Parts Manual for KE7, KF7 and KG7 series is essential unless
you know them well enough to work on them blindfolded,
Almost anyway,
Good Luck
Louis
Louis

[Tubs]

Not an authority but have a little experience. I did some videos. I’ll post links when I get home tonight or tomorrow.

A "Boathouse Repair" is one thats done without having tools or the skills to do it properly.

[Tubs]

These are a couple of things I learned from the ones Ive had. If you heat the gear case with a heat gun, the cartage that you had to use a puller to get out, will drop back in. https://youtu.be/TvZdUuhJAgU A piece of pvc tubing is really helpful getting the impeller in. https://youtu.be/twwfih7y7ZA

A "Boathouse Repair" is one thats done without having tools or the skills to do it properly.

[Tubs]

 

To me the most important service you can perform on these is replacing the upper and, especially the lower, crankshaft seals. I’ve had both of my motors quit when this seal failed. One I had replaced when I restored the motor 5 years earlier. The other was a running motor when I got it. It ran almost six weeks before it quit. Symptoms were identical on both motors. I describe them in this video.  https://youtu.be/3aEQ773QzuM  

A "Boathouse Repair" is one thats done without having tools or the skills to do it properly.

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Mallett

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