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Welding a piston

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  • Welding a piston

    I managed to burn a 1/2 in hole in the top of my new piston. This is for a old 250 cc yamaha. This motorcycle is not a restored garage queen, but I just redid the top end. It is one I plan to ride now, and then. So to the piston problem. Because of a lean carb mixture the motor over heated and burned a hole in the piston. What would be the possibilites of welding the hole, and having the piston be good enough to last? I do plan to find the carb problem. I need to richen it up a bit.The piston is aluminum. A friend of mine has a good TIG welder, and more than likely not charge much if anything. Stan

  • #2
    Not having direct experience, I would think it is certainly possible with service time ranging from a few minutes to many years! I have seen some amazing repairs, including a hole brazed up in a cast iron piston without removing it. I successfully repaired two deep pin scores in a Mopar 360 cylinder with JB Weld and a friend put many miles on a Mercedes diesel with one of the rod bearings shimmed with a business card. Be aware that the rings may have lost their tension, as I have experienced that without piston damage in overheated auto engines.
    Don Young

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    • #3
      You should be able to weld it, but I doubt the piston will retain it's original dimensions.

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      • #4
        It ay not be the carb. A leaking gasket or crank seal can lean it out also.
        Jon

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        • #5
          Is it a dt250???reed or piston port???what size is the bore???? (70.??) Ihave lotsa spareslet me know...Shawn

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          • #6
            new pistons aint that expensive.... if you can get one?

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            • #7
              Ya might want to concider where the 'hole' went to! Some of it may be in the crankcase. Not all of it will vaporize or be exausted out. I ain't familiar with that motorsickle, but I have seen the results of others with melted pistons. You will need to see that the main bearings are chip free!
              Krutch


              Mentally confused and prone to wandering!

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              • #8
                I have repaired lean-burn holes in H-d pistons. Here is how it went.

                Soak the piston in rubbing alcohol overnight to remove the gas\oil contamination
                Place the piston in a ring compressor wrapped with a wet rag to work as a heat sink.
                Ground DIRECTLY to the piston skirt to prevent any errant arcing
                Use small, controlled blast deposits to the hole and allow to cool to touch( Weld nuggets no bigger than a peanut)
                Polish and machine as needed.
                Be careful of burn-through as it may alter the balance of the piston and directly impact the entire recip assembly. Basically, make it look like you were never there. Die grinder, Dremmel tool, axe, hatchet, what ever means you deem needed.
                Best o' luck. Anything I can do to help, drop me a line.

                Cy

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                • #9
                  I've had good luck with welding pistons, my method is to clean the top of the piston with a aluminum cleaner or hydrocloric acid and then wash after wards with hot soapy water.
                  I have different welding fixtures for each size piston that keeps the piston true. Since going this route I haven't had a piston warp yet.



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