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    50cc rebuild/upgrade problem

    I have a 139fmb 50cc 4 stroke 4 gears semi auto electric under/kick on a mini chopper. Piston and cylinder and connecting rod bad. Ordered a new crank didn't realize it was a 49.5mm stroke till after I installed it when the 39mm piston pop out the top of cylinder.what would I need to get to...
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