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Machined stuff today!

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  • Machined stuff today!

    Burnt up a piston while out on the water last weekend. So stuff happened.

    Got home a little earlier today from work. Piston was sitting on the kitchen counter! So I went at it this evening!

    The scoring and everything packed with paper towel.



    The sunnen set up and ready to start work.



    After only about 50 revolutions of the hone.

    Andy

  • #2
    The pistons, old and "new".



    I only had to go .010" deep to get rid of the scoring so I had to take .020" off the piston. The .030" over is thicker than the stock piston by .020-.022". I put the same "ribbed" surface back into the piston.



    Cut the square ring .020" deeper to clear. Also cut the tapered ring groove deeper and a hair wider.



    Rings gapped, rod swapped over (hole facing up) popped in and rod cap torqued to 44ft/lbs.

    Andy

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    • #3
      All back together (minus intake side in pic).



      Started it up on the muffs tonight and made all the adjustments again. Running on the muffs with no coughing or popping! Can't wait to try it on the water again!

      Taking apart and putting back together the intake was the hardest (most time consuming) thing of the whole deal.
      Andy

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      • #4
        Would have thought those pistons would have been cam ground. Hope turning it round works for you.

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        • #5
          Originally posted by Gary Reif View Post
          Would have thought those pistons would have been cam ground. Hope turning it round works for you.
          Ditto that Gary!

          I'm not quite sure what I saw in the fotos, But "clearance" is not your friend in fitting two stroke pistons. Tight is right!

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          • #6
            Originally posted by Gary Reif View Post
            Would have thought those pistons would have been cam ground. Hope turning it round works for you.
            Ditto that Gary!

            I'm not quite sure what I saw in the fotos, But "clearance" is not your friend in fitting two stroke pistons. Tight is right!
            Any blow by leads to scuffing. Those "marks" after honing are the deaths knell.

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            • #7
              Originally posted by Gary Reif View Post
              Would have thought those pistons would have been cam ground. Hope turning it round works for you.
              Yep, more often than not the piston is oval instead of round and tapered so that skirt diameter is bigger than top. Albeit can't tell for sure, maybe OP turned the piston to tapered shape.
              Location: Helsinki, Finland, Europe

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              • #8
                I don't post much but read the forum everyday. I'm curious, Are you using gas with ethanol in it?

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                • #9
                  Book says piston cannot have more than .002" taper from top to bottom. .004" taper allowance on the cylinder. There is a .005" piston to wall clearance which is on the tight side of the book spec.


                  Jeff, yes we run 10% 87oct. I am not excited about it but it works. We run it in our work boats and never had an issue with it yet. I also don't feel this burn down was because of the fuel either. The reason why is I have been having an issue with this motor since I swapped it over. I have been chasing a coughing problem (lean) at idle and have done everything but stupidly not check the compression. So now I feel the cylinder may have been weak this whole time causing the coughing and just went finally. The other cylinders look perfect.
                  Andy

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                  • #10
                    Originally posted by CalM View Post
                    Ditto that Gary!

                    I'm not quite sure what I saw in the fotos, But "clearance" is not your friend in fitting two stroke pistons. Tight is right!
                    Any blow by leads to scuffing. Those "marks" after honing are the deaths knell.


                    I didn't stop honing after that first pic. I went another .005" deeper till all the marks were gone. I also then finished off with a J85 stone so the hone finish was extra smooth.

                    I have done this process before and have had great luck. I rebuilt one of our "parts motors" to use on our fishing boat. Has been going strong for years now. I do know about all you mention though. 2 cycles even though simple are quite finicky with their only moving parts.

                    This triple had similar scoring and went threw the same processes as the V4.

                    Andy

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                    • #11
                      Nice job.

                      Meh, stuff wears out, you fix it.

                      To me, it looks like a lubrication failure. Room for improvement? Do these require you to mix the fuel, or is there a lubricant mixing/injecting mechanism like my old Yamalube bike?

                      I have this suspicion that what the wear engineer wants for lubricating oil amounts, and what the nice government regulators require are different numbers, so there's that...

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                      • #12
                        cool beans! It's great to be able to fix your own stuff, whether it's a broken spoke on a bike wheel or a seized piston in an outboard motor. The latter is quite a bit more impressive mind

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                        • #13
                          Originally posted by michigan doug View Post
                          Nice job.

                          Meh, stuff wears out, you fix it.

                          To me, it looks like a lubrication failure. Room for improvement? Do these require you to mix the fuel, or is there a lubricant mixing/injecting mechanism like my old Yamalube bike?

                          I have this suspicion that what the wear engineer wants for lubricating oil amounts, and what the nice government regulators require are different numbers, so there's that...
                          This is an "oil injected" model, DRO is what they call it. It is not actually "oil injected" as they say. What it does (or supposed to do) is mix the right amount of oil and gas after the fuel/oil pump which then goes into the carbs. Depending on the vacuum pulse of the motor regulates (they say) the amount of oil mixed into the fuel. Many many people eliminate the oil side of the pump and just mix the fuel themselves. I have done this as well on the triple I posted a pic of earlier as its oil pump is shot.

                          However with this V4 the fuel/oil pump work very well. I can tell by the amount of oil being used in association with the amount of fuel being used. I have a couple suspicions of either a prior overheat or a prior loss of oil (PO forgot to fill the tank). But with the good condition of all the other cylinders I have a hard time believing either. I ave checked all the carbs multiple times and there is no debris or obstructions. It is odd this one cylinder burned up and the others are so perfect yet. The carb is neither at the top or the bottom of the feed line either for this cylinder.
                          Andy

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