Piston and rings question

[weezzell_5400]

Ok so the motor is a 1987 120hp evinrude ....small bore ....here is my spill....the motor had low compression when I got it a few days ago...all cylinders around 58 to 60 psi....checked with 2 separate gauges....its been sitting up for about 7 or so years ...but has great potential...has an awesome spark ...and overall everything looks great ....so I pulled out the telescoping gauges and the micrometer ....and the cylinder walls are reading right around 3.4975 ...and one right on the dot of 3.5000.....so the bore of this motor is supposed to be 3.5 stock....so my question is ...can I replace just the rings ...or are the rings specific to each piston and have to do full piston and rings ....the walls of the cylinders look great ...but one has a little rust or something at the very edge that can be cleaned up with a light honeing ....

 

[jimmbo]

Before ripping the engine apart to rering, you say the bores aren't scored? I suggest a good decarbing of the rings, by spraying some Engine Tuner or another Combustion Chamber cleaner into the cylinders and letting it soak a few days, then doing a standard decarb spraying the stuff into the carbs. Myself, I wouldn't be too concerned about a teeny tiny bit of dust rust, But if the cylinder looks orange, well...

 

[Faztbullet]

If that motor has had any use the top of cylinder will measure bigger than bottom as these wear at a taper, all came from factory 3.500 so cant measure under size. Measure top,middle and bottom of cylinder at 12 and 6 and 9 and 3.

 

[Silvertip]

Yes -- you can re-ring without replacing pistons -- provided you use rings for whatever piston is in the engine which may be stock, .010, .020, .030 oversize etc. You cannot put oversize rings in a standard bore engine, nor can you put standard size rings in an oversize bore.