1968-72 johnson 25hp outboard piston/ring issues

[sea assassin]

So i've got an old 25 hp johnson sea horse im working on rebuilding. I purchased it used and it has the metal tag ripped off of it so i'm not 100% sure on the year, but from my research it fits in the 68-72 range. Anyways it has bad compression in one piston. Pulled it and it has some marring on it, but nothing too bad so i'm working on replacing the rings. From my service manual it shows to have 2 rings only. My pistons both have 3 rings. I'm lost as to what to do. only numbers i could find on the piston are 307846 and on the connecting rod 307847. I've searched all over to find more info on them, but haven't found a thing. Anyone know what this could have come from or where to get rings to replace them. (purchased a set of oem rings to see if they would fit and they are much too small). thanks for the help.

 

[milliesdad]

Re: 1968-72 johnson 25hp outboard piston/ring issues

Could be that you have a commercial model? I've had several of these apart- same year range- and I haven't run across a 3 ring piston. I beleive -and I will be corrected if wrong- that the commmercial motors of this vintage were gray and have a 3 eared cllutch dog.

 

[boobie]

Re: 1968-72 johnson 25hp outboard piston/ring issues

Have you tried Shop.Evinrude.com with your approx yr and hp to find any three ring pistons??

 

[sea assassin]

Re: 1968-72 johnson 25hp outboard piston/ring issues

i've looked ALL over for any 3 ringed piston and can't find a thing. My pops thinks they could be aftermarket racing pistons because it has 3 rings instead of 2. The rings on it are much wider than the standard rings for this model motor. I just want to get some good compression on this bad boy again and get it running good. Thanks for the help so far guys keep the advice comin. Here's a shot of the motor as well.

 

[dew2]

Re: 1968-72 johnson 25hp outboard piston/ring issues

Have you looked at the welch plug on top the engine 1/3 way forward of the spark plug.It should have the model and ser# stamped into it.