Hole in my piston! Mercruiser 120hp 2.5 with pre alpha outdrive!

[dominick19m]

my 120hp mercruiser 2.5 with hole in the piston in my 67 sterncraft

im wondering since this motor has a solid bottom end with no knocking can i replace the piston head and put the old rod and new or old rod bearings back in and get this thing running without getting the crank serviced or removing the other pistons or should i remove them all and get new bearings? Can i put new bearings in without getting the crank turned.? Im not sure that it matters my crank has zero damage there was no knock and the bearings show little wear i have next to no money for this.. Has anybody ever fixed a piston and put the old rod and bearings back in? Thanks for ur info and opinions

p.s. i did replace water pump and fuel pump to make sure it doesn't happen again..anything else that could cause it and could be done to prevent it in the future plz advise i just bought this boat its a gorgeous old boat for its age i just hope i can give it a few more yrs! i checked the bellows anything else on this boat i should check before hitting the water?


HAHA just found out its a mc-1 outdrive im learning already...!
​

 

[achris]

Re: Hole in my piston! Mercruiser 120hp 2.5 with pre alpha outdrive!

Hello Dominick.

Replacing just the one piston is not a problem, as long as it's the same weight as the others. If it were mine, I'd replace all the piston rings and hone the bores. If the bearings are very good, by all means reuse them.

Chris......

 

[Bondo]

Re: Hole in my piston! Mercruiser 120hp 2.5 with pre alpha outdrive!

Ayuh,.... I agree with Chris, changin' out a single piston is an option, so long as it's Exactly the same piston,....

That's no doubt caused by Detonation,.... probably from a Lean condition,...
Test the fuel system, insteada just Hopin' it was the fuel pump,...

 

[harleyman1975]

Re: Hole in my piston! Mercruiser 120hp 2.5 with pre alpha outdrive!

Were all the spark plugs the same? Was there a leak in the head gasket? What was the condition of the valves on the cyl that burned down?

 

[Volphin]

Re: Hole in my piston! Mercruiser 120hp 2.5 with pre alpha outdrive!

Just for giggles get a set of 4 pistons & rings. Reuse the bearings if not badly scored.

 

[dominick19m]

Re: Hole in my piston! Mercruiser 120hp 2.5 with pre alpha outdrive!

im not 100 percent the plugs belonged they wur all new but seem to be pretty long on the bottom also the fuel pump was no good thats why i replaced.. i could do all the pistons if i could find them cheap could i use the ones out of a old chevy II with the 2.5? if so i found some cheap valves all looked good no burned ones head gasket was also decent i have never had it running so i dunno as to what could of caused it..i intend to go thru everything that is suggested..any idea as to how the carb should be set i would like to check the needles when i get it back tog pretty sure they have been adjusted by previous owner...

 

[harleyman1975]

Re: Hole in my piston! Mercruiser 120hp 2.5 with pre alpha outdrive!

if carb problem it would be a high speed jet issue most likely caused by a dirty or partly plugged jet (or god forbid somone changed the carb with the wrong replacement).

 

[Bondo]

Re: Hole in my piston! Mercruiser 120hp 2.5 with pre alpha outdrive!

im not 100 percent the plugs belonged they wur all new but seem to be pretty long on the bottom also the fuel pump was no good thats why i replaced.. i could do all the pistons if i could find them cheap could i use the ones out of a old chevy II with the 2.5? if so i found some cheap valves all looked good no burned ones head gasket was also decent i have never had it running so i dunno as to what could of caused it..i intend to go thru everything that is suggested..any idea as to how the carb should be set i would like to check the needles when i get it back tog pretty sure they have been adjusted by previous owner...

Ayuh,.... Most of the Info ya need for the carb is in the instructions that come with the Rebuild Kit,...

The factory Manuals for yer motor can be found up in Don'S Adults Only section at the top of this forum,...