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Thread: Two-stroke piston slap?

  1. #1
    Join Date
    16th April 2011 - 11:22
    Bike
    1978 Yamaha RD250E
    Location
    NZ
    Posts
    197

    Two-stroke piston slap?

    Hey all, I've got an issue with a rattle or a clicking sound in the left cylinder of my RD250.. The sound is only present below 3,000RPM and it seems to be rhythmic and in time with the engine. I popped the heads off to have a look at the pistons and my left cylinders' piston has a little bit of play in it. They're both .25mm oversize but the left piston looks like it's second hand or something weird. Certainly more worn than the right. There's evidence of back-blow into the cylinder too, suggesting that the rings and piston clearance is a bit too high. My question is, what does piston slap sound like and would it be more prevalent at low RMP/idle rather than high RPM? Is it rhythmic or random? I'm having trouble discerning this noise from a top end bearing/gudgeon rattle... The cylinders barely have any wear on them. There's no lip and I can still see the scouring marks too. Am I best off reboring to 0.5mm or could I get away with popping in a new 0.25mm piston and rings into my left cylinder? Thanks!

  2. #2
    Join Date
    17th February 2005 - 11:36
    Bike
    Bikes!
    Location
    Christchurch
    Posts
    9,605
    Only you can answer that, measure it up.

  3. #3
    Join Date
    25th April 2008 - 23:01
    Bike
    KTM 950SM, '78 X7, FZ750, GN250
    Location
    Wellington
    Posts
    693
    Rebore on both, keeps the engine balanced

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