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Mid 80s 60hp #1 piston started melting

C

C_roy08

New member
Hi guys, trying to get some help to why my piston started melting on #1 cylinder of my 84 60hp merc. Was running great then started throttling down and it lost power, after getting in home pulled plugs and found #1 plug was coated with aluminum, shined flash light in plug hole and the ridge that's on top of the piston has about a 1/2 spot where it has been ate out, also pulled exhaust cover to get better look, cylinder walls appear to be ok on all cylinders, 2 and 3 exhaust ports are pretty clean and #1 has a noticable amount of carbon build up on it. Motor always started and ran great, had one spot when coming up on plan that the motor would loose power but always pulled out of it
If anyone would have a idea on what might have caused this it be much appreciated, thanks
 
Unfortunately that's typical of those motors. Not only is the impeller is too small for them, Merc made the dumb mistake of sending some of its desperately needed cooling water through the fuel pump. (That line needs to be plugged off!)

The PH has to come apart. With some luck a new piston and a hone job will make it run again--I've rescued several that were that bad.

Jeff
 
fastjeff said:
Unfortunately that's typical of those motors. Not only is the impeller is too small for them, Merc made the dumb mistake of sending some of its desperately needed cooling water through the fuel pump. (That line needs to be plugged off!)

The PH has to come apart. With some luck a new piston and a hone job will make it run again--I've rescued several that were that bad.

Jeff
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So the water line to the fuel pump can be plugged off is what your saying right?
 
Fazbullet, would that be a weak ignition system
Click to expand...

No..it would be a over advanced timing issue such as trigger or bad switchbox(bias)
. All the ones I have worked on that had pre-ignition have been ignition issues and have never plugged the fuel pump water line as it was designed to cool pump and prevent vapor lock.
 
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