I am pretty sure that you can use the 3 ring in place of the 2. Have heard others discussing this. Let me do some checking.
The old 2 ring pistons required 16:1 fuel ratio. That's a pretty old mower you have. Somewhere in the mid-70's they went with the 3 ring pistons and 32:1 fuel ratio. If I were you, I would get the part # of the connecting rod your mower takes. Then compare that to a later model D series engined mower with a 3 ringed piston. R7266 is a model mower you can use to look that information up. If the #'s match, you're good to go. Good luckhi all i am restoring my second lawn boy. it has a d449 engine with a 2 ring piston. now i couldnt buy a new piston from lawn boy so i purchased one from tulsa engine warehouse. the piston clearly stated that it replaces lawn boy part # 606607 which is what mine calls for, however the picture of the piston depicts a 3 ring piston, i have found many other aftermarket pistons that replaces the #606607 piston that is a 3 ring not a 2 ring. my question is will it work? here is the link Piston Assembly Replaces Lawn-Boy: 606607 please help thanks much
Thanks for clearing that up. I was backwards with my infoIf you ordered a 606607 piston from Tulsa then you will be getting a 2 ring piston. I just ordered 3 from there and recieved them yesterday. A good looking piston to I might add, I just hope that it will last like the original OMC pistons. The ring gap checked good (.015-.025). What Brad said is exactly right, the 3 ring piston and 2 ring piston are not interchangeable. If you want to convert from the 3 ring to the 2 ring piston, or vice versa, then the connecting rod would also have to be changed, the wristpin on the 2 ring setup is slightly bigger than the 3 ring setup. Not sure why anyone would want to convert from a 2 ring to the 3 ring though, since the 3 ring does not have the needle bearings in the small end of the connecting rod. Most folks convert from the 3 ring to the 2 ring because of the wristpin needle bearings, and it enables the motor to be run at 32-1, instead of the 16-1 that was recommended with the 2 ring piston. From my experience with these old 16-1 machines is that with the plain bearing wristpin, it causes the hole where the wristpin goes through the piston to become elongated, whereas with the 2 ring piston the wristpin doesn't really rotate against the soft aluminum piston boss, so the small end of the connecting rod will last much longer with the needle bearings installed.