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Rebuild Question Johnson 115, piston sizes. hopefully not a dumb question here

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  • Rebuild Question Johnson 115, piston sizes. hopefully not a dumb question here

    My 115 teardown (first time) went smooth and uneventful. I had 1 outter ring break (prior to my purchase) it tested fine and had good compression. When I got into it, it Had no damage other than a pocked head and Piston. Walls very smooth.

    My plan was to replace offending Piston & Head, hone and ring all 4 holes. However, Since I cant be sure of any previous work, I cant be sure what sizes are in there from the past.

    I'm assuming a good practice would be to baseline the whole thing--Meaning I should take it to be measured fully (pistons and holes). Rings are sized to specific Piston sizes right? If there was an oversize in there already I wouldnt know it, and I'd probably put the same rings on all 4 inadvertently. Going to have them clean it, and take out 2 broken Mount bolts too.

    Ha...as I write this, I'm answering my own question I think!!!!!

    Also, while this is opened up-is there anything else I should replace that one would consider critical. I'll spend some, but dont want to replace everything just to do it.

    Thanks

  • #2
    Re: Rebuild Question Johnson 115, piston sizes. hopefully not a dumb question here

    Clean the top of the pistons. If it has been bored before, the pistons usually have the size stamped on them. .20. .30. Or .40.

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    • #3
      Re: Rebuild Question Johnson 115, piston sizes. hopefully not a dumb question here

      you would certainly need to tell ius what year and model # the motor is...then we might be able to tell you right off what the dia is supposed to be from the factory.

      bob

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      • #4
        Re: Rebuild Question Johnson 115, piston sizes. hopefully not a dumb question here

        Originally posted by bob johnson View Post
        you would certainly need to tell ius what year and model # the motor is...then we might be able to tell you right off what the dia is supposed to be from the factory.

        bob

        Thanks, 1984

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        • #5
          Re: Rebuild Question Johnson 115, piston sizes. hopefully not a dumb question here

          Originally posted by Capt Ken View Post
          Clean the top of the pistons. If it has been bored before, the pistons usually have the size stamped on them. .20. .30. Or .40.
          Hmm, Thanks. Will clean the tops and see. I'm thinking it will still be good idea to take it to be fully measured and go from there. Thay way I'll truely know the shape of the holes and know what parts to purchase.

          thanks for the feedgack

          Comment


          • #6
            Re: Rebuild Question Johnson 115, piston sizes. hopefully not a dumb question here

            I'm thinking it will still be good idea to take it to be fully measured and go from there.
            That the only and correct way to rebuild one....
            When in doubt,Trim it out!!!
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            • #7
              Re: Rebuild Question Johnson 115, piston sizes. hopefully not a dumb question here

              Originally posted by rothfm View Post
              My 115 teardown (first time) went smooth and uneventful. I had 1 outter ring break (prior to my purchase) it tested fine and had good compression. When I got into it, it Had no damage other than a pocked head and Piston. Walls very smooth.

              My plan was to replace offending Piston & Head, hone and ring all 4 holes. However, Since I cant be sure of any previous work, I cant be sure what sizes are in there from the past.

              I'm assuming a good practice would be to baseline the whole thing--Meaning I should take it to be measured fully (pistons and holes). Rings are sized to specific Piston sizes right? If there was an oversize in there already I wouldnt know it, and I'd probably put the same rings on all 4 inadvertently. Going to have them clean it, and take out 2 broken Mount bolts too.

              Ha...as I write this, I'm answering my own question I think!!!!!

              Also, while this is opened up-is there anything else I should replace that one would consider critical. I'll spend some, but dont want to replace everything just to do it.

              Thanks
              from all that i have heard, one thing to make sure that is new and working properly is the water diverters...

              I dont have them on my motor style...but those crossflows had them and they seemed to be a problem area

              bob

              Comment


              • #8
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                Re: Rebuild Question Johnson 115, piston sizes. hopefully not a dumb question here

                Originally posted by bob johnson View Post
                from all that i have heard, one thing to make sure that is new and working properly is the water diverters...

                I dont have them on my motor style...but those crossflows had them and they seemed to be a problem area

                bob
                Oh yea, very familiar with the diverters. I was actually surprised to see they are still round. Replacing anyway. A very important item for sure.

                Thank you. Got all the pistons out, everything labeled and in bags. Going to take it to a shop for cleaning, and measuring.

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