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Thread: Mercury 402x 35ss

  1. #11
    Administrator Ron Hill's Avatar
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    Nov 2004
    Tustin, California
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    Default 402 XS Was Really A "JUNK" Motor

    By the time the 402XS came out Mercury was moving away from the "Direct Charge: Pistons, and building V6 motor.

    Most 402 XS's that I knew about broke the sleeves around the exhaust ports. We kind of surmised that the exhaust was getting out fast enough and the engine developed enough heat to crack the struts in the ports.

    My dad being the engine builder that he was, noticed a drop in RPM when the engine warmed up. HE SPENT MANY HOURS RUNNING MY MOTOR IN OUR TEST TANK.

    In the spring of 1977 I broke Kilo records in 35 SS Hydro and 35 SS Runabout. I out ran BOB WARTINGER'S TIME IN 35 S HYDRO.

    The one thing we didn't know was that gapped plugs would run in a surface gap motor. Clark Maloof taught me that after he beat me at the 1977 National. I could beat him o the turn but my surface gap plug would load in the corners, and Clark would drive around me...

    Replacement locks were expensive and didn't last very long. Most 402 XS's got switched to 55-H's or D Motors, a fishing blocks were made legal and powerheads were everywhere, cheap!

  2. #12
    Team Member ice_spy's Avatar
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    Aug 2009
    NSW Australia
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    Thanks Ron, that gives me a bit of an idea about the days when this motor was being run. So the 35hp performance was ok ? Top mph ? Would it rev up quick enough out of the corners ? Or bog down and take time to reach top end ?
    I read this motor suffered from the heavy flywheel ? Or was that the early 4 cylinder 402? Was the inertia problem only present on V hulls ?
    It was quickly coined as a failure with Mercury as it was coming back with broken crankshafts, when loaded up low rpm ONLY. Apparently due to a lack of center bearing crankshaft support. The starter motor broke its brackets, and was resolved by fitting an extra lower strap clamp to the motor.
    The exhaust port windows (3), look very small to me and could be a choke point for heat. I intend to port the exit casting alot. There is ways to reduce the temp on the exhaust side cylinder walls, I may have to incorporate this into the build.
    The race never stops

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