Piston Scoring

[Jho928]

What is the determining factor for piston replacement.I have a spare block 4 pistons and crank for a 35 hp BT that i wish to assemble.All of the pistons exibit some scoring (some worse than others )I guess my question is How much is too much? Also this is a 57 BT 35 hp Mod#25930 and new pistons are NLA ??? Also what is the paint or coating that is on the inside of the block and head .One head I have has no more on it after cleaning the carbon off it.Thanks Jim

 

[ledgefinder]

Re: Piston Scoring

You should be able to get those pistons easily, aftermarket - try the antique outboard sites.<br /><br />On 2-stroke karts engines, Yamaha used to say if you can remove the scoring with 600 grit wet-and-dry, then it's OK to reuse the piston. That assumes the piston still mikes up OK, and the ring lands look very good (really the most important part).

 

[Chinewalker]

Re: Piston Scoring

Hi Jim,<br /> I've used lightly scored pistons that have cleaned up with 180-grit sandpaper. I do it in a cross-hatch pattern, 45-degrees to the direction of travel. This accomplishes two things - it cleans up the piston, and creates a rough-ish surface to hold oil. <br /> As was pointed out, the key is to get the ring grooves PERFECT. You don't want a scorched over ring groove sticking a ring first time you run it... Use an old, broken ring to clean the grooves and test for fit...<br />- Scott

 

[Jho928]

Re: Piston Scoring

Thanks for the info ,I think i'll try to find NOS pistons first (it's a small price to pay for peace of mind)Any suggestions on were to try?<br />Also as for the paint or coating inside the block(looks like red primer,but i'm sure it's not primer ?) What is it? ,and can I get it to reapply to the inside of a head?

 

[R.Johnson]

Re: Piston Scoring

I have never seen anything in writing what the red paint is. I just assumed it was a sealer they used to guard against any porosity that might be present in the cast aluminum block, I would'nt worry about putting it back on the head.

 

[Paul Moir]

Re: Piston Scoring

A couple places to try:<br /> PartsForOutboards <br /><br />Twin City Outboards <br /><br />Laings Outboards <br /><br />Good luck!