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Yamaha OX66 Piston

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  • Yamaha OX66 Piston

    So, I think I pretty much know this motor is shot after just 800 hours but I'm not sure what would cause this piston to project so far out of the block. Seems like it was getting plenty of lubrication and it doesn't look overheated. It was definitely hitting the head. Shame because the rest of the cylinders are fine. Bad crankshaft bearing?

  • #2
    crankshaft bearing sounds like a real good guess. Report back when you get deeper into it.
    Rick Loszewski[br]Derry, NH


    • #3
      rod bearing or wrist pin bearing
      76 25 \"Aenigma\"[br]73 17[br]Richland/Long Beach, MS[br][br][br]17 project[br]


      • #4
        The piston was not directly hitting the head, but did ingest and hit some foreign object which moved around a bit before finally getting spit out the exhaust port. Likely the rod bearing or a piece of a broken ring. You can tell by rolling the motor over slowly until the piston starts to travel back down, stop and try pushing the piston a little with your thumb. If there is rod clearance you will discover it then, as it will move in easy until the clearance is taken up. When a rod bearing fails on a two stroke it gets moved around and up through the intake ports and finds its home at the top of the piston. two stroke rod bearings are needle bearings contained in a shell. Dont rebuild the engine unless you have your injectors all checked, to find the source of the problem.
        [br]1994 Mako 215 Dual console Optimax 225[br]1978 Mako 19 with 90hp johnson[br]1996 Mako 22[br]1982 Mako 171 Angler 135 Black Max Mercury[br]1987 21b 225 Yamaha[br]1974 23 inboard Gusto gone.[br]1979m21 225johnson \"blue dolphin\" bought off this board and restored [br]with everyone\'s help!!Gone but not Forgotten....[br]1979 20 Mako 115 Suzuki gone[br]1977 19 Mako 115 Johnson gone[br]1976 23 Mako twin 140 Johnsons gone[br]1983 224 with closed transom and bracket[br]And 162 SOB (some other boats)[br]Venice Florida, Traverse city Mi.