1985 Mercury 60HP 2 Stroke (3 Cylinder) Piston Repair

wrobdog

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Apr 28, 2008
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Had a major brain fart this weekend and messed up the first cylinder piston head (Don't Ask). I'm ok with engine repair but before I buy the manual and parts, I'm wondering if someone could tell me how difficult the repair would be or should I take it to a professional? The If I attempt the repair should I replace the other cylinder piston rings even thou they seem fine?

Thank You,
Rob
 
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Faztbullet

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Gotta ask as there is no head on this motor. If cylinder walls as damaged it will need bored which is not a DIY project.
 

wrobdog

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I should have said the piston high dome in stead of piston head. Would it be minimal teardown to determine if the cylinder wall is damaged? So you're saying if the cylinder wall isn't damaged it's most definitely a DIY project?
 

jerryjerry05

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I think this motor you need to pull the piston out from the front.
Thus it's not gonna be real easy.
Got/get a bore scope?
Look inside for damage.
If you can shine a light inside the plug hole and see any damage to the piston???
Then you possibly have cylinder damage??
Like Fazt said cylinder repair ain't a do it yourself repair.
 

wrobdog

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Using a flashlight I can visually see a small pit on the dome, I may track down a bore scope to be sure I damaged the cylinder. I may have more questions after the bore scope. Thank you for the replies
 

undone

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I know you said don't ask, but without knowing what you did to damage it it's a little difficult to say how hard it will be to repair.
 

wrobdog

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Long story short, I forget to add the proper amount of 2 cycle oil in 1 of my 2 six gallon tanks. I have owned the boat for 15+ years and have never made such a bonehead move, i'll never do that again.

I was able to borrow a bore scope and the #1 cylinder wall shows no visible damage, thank goodness. Just debating on whether to make this a winter project or have a shop deal with it.
 
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undone

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A small pit on the dome of a piston that has been run with too little oil can be a couple of things. If the motor gets too hot it can burn a hole in the top of the piston, in this case you may have shut it off soon enough for it to not melt through. Or, it can mean a piece of something else broke off and bounced around inside the combustion chamber, bearings, rings, locating pins, etc. If something broke and bounced around inside it will have also damaged the head, which I think on this motor means a new block.

Did you check the compression?
 

racerone

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Saying that you did not add the " proper amount " does not help here at all !!!---post how much oil you used.----Do a compression test on the motor and post the actual values you observe.----That pit in the dome may be from a " machining centre drill " and is normal.
 

wrobdog

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As for the amount of oil, the tank was a ¼ full from last weekend and I added an additional 9.6 oz of 2 cycle oil and topped off with fuel.

I first noticed something on Saturday after a long day of fishing, returning to the boat launch the engine lost all power and would only run at trolling speed. Didn€™t think anything of it until I discovered the problem during winterization when I noticed some aluminum almost fused on the spark plug end and the pit is very noticeable right beneath the spark plug.

Undone - I think you're right about shutting it off before it did serious damage, but then again I won't know for sure until I complete the compression test.

I will post the compression results next weekend.
 
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racerone

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You need to post exact and complete information !!--------How BIG is the tank ?--How much fuel did you add ???------The aluminum tranferred to the plug does sound expensive !
 

wrobdog

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Performed the compression test with the throttle at full and holding 4-5sec for each cylinder. Cylinder #1 had the piston problem so I dodged a bullet. Figure while I'm replacing the #1 piston I should also replace #2&3 rings.

First Test = 1- 130psi , 2- 135psi, 3- 132psi
Second Test = 1- 132psi , 2- 138psi, 3- 135psi
 

undone

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Some pistons have a very small machined depression in the center of the dome, so if it's a perfect pit it could be that.
 
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