Replace this piston?

[Grumpy Bear]

Hello all. I'm rebuilding the powerhead of a 1974 Merc 500 50hp. One of the pistons I know I need to replace (and not just the rings). Another, however, had good compression but when I looked at it, it was pretty scuffed up (it was next to the other piston that was pretty much fubar). I've attached a pic. Can I get away with just replacing the rings on this thing?

Thank you!

 

[MTboatguy]

Well, you could probably get away with it, but this far into a motor, I would replace both of them, normally when I am rebuilding motors, it s just habit, I replace the pistons, they are really in the whole scope of things not that expensive and the piece of mind is worth it to me. What do the cylinder walls look like?

 

[Grumpy Bear]

Thanks for the reply. The cylinder walls look great. I do plan on honing any glaze off them.

 

[merc850]

I would retime the engine and make sure you have a new impeller and the right plugs installed from what I can see.

 

[gm280]

It would be a lot easier to answer that question if you could clean the piston up so we can see if there are some serious scratches on the piston. But it could clean up well and look nice...we just can't ell from that picture. I'd take the time to soak and clean them first and see what you're dealing with...

 

[Grumpy Bear]

Thanks for everyone's replies -- really appreciate it!

 

[Faztbullet]

(1) You aint going to clean that piston up (2) The cylinder walls will have some grooves and transfer in it (3) You wont clean it(cylinder) up with a spring or ball hone you will need a ridged hone. I have 2 STD Vertex pistons that still have some of the break-in coating and I know their good as they have been spun up over 8000rpms.

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