Question about piston rings....

[FoolOfAFisherman]

I'm doing an overhaul on my motor and I've noticed that several different piston part numbers are applicable to my motor. Can you use a 2ring piston to replace a 3 ring piston and what would be the disadvantages of this? It's a '73 1150 115. SN3027266

 

[paultjohnson]

Re: Question about piston rings....

On another small engine i was rebuilding [non-marine]. A single ring piston version was available to replace the stock 2 ring piston. According to that source, switching to a single gave a little better top end. Im sure there is more to it, but thats one thought........

 

[FoolOfAFisherman]

Re: Question about piston rings....

My thought was that, just like the needle bearings, if you replace one you replace them all because you want there to be an equivalent distribution of stress across all pistons. I was thinking that with 2 piston rings, you would have less compression which would cause there to be an unequal distribution eventually resulting in engine failure. Any thoughts on this?

 

[FoolOfAFisherman]

Re: Question about piston rings....

I was told that the three ring pistons for my motor are NLA and that the two ring pistons are all I can buy for it. Anyone know this for sure?

 

[Faztbullet]

Re: Question about piston rings....

The 2 ring piston will work fine and it may have a little lower compression if you use a low dome piston.

 

[FoolOfAFisherman]

Re: Question about piston rings....

ok..thanks for the info..im gonna need it

 

[Droll]

Re: Question about piston rings....

From the service bulletin about the 2-ring pistons

MARINER AND MERCURY 35 THRU 150 (IN-LINE)
Piston assemblies with half keystone rings are now available
as service replacements, on models listed. The half
keystone ring design is more resistant to carbon sticking
than the previous rectangular ring design.

QUICKSILVER:
NOTE: Half keystone two ring pistons and rectangular
three ring pistons may be intermixed in the same engine.
Piston assemblies with half keystone rings, will supersede
the corresponding piston assembly with rectangular rings.
PRODUCT IMPROVEMENT:
Piston assemblies with half keystone piston rings, are offered
as a product improvement and are not covered by
warranty to up-grade previous models.

2-ring pistons high dome...
774-9137A12 STD
774-9137A13 + .015"
774-9137A14 + .030"

OR you can use pistons from a 3rd part, some of them still got 3 ring piston in stock
Sierra Marine, ProMarine

Wiseco ( inline engines... )

Arne Kjetil