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Thread: Mercury 402x 35ss

  1. #11
    Administrator Ron Hill's Avatar
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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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    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

  3. #13
    Richard Sacher curbman's Avatar
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    So how did you make out with this build any follow up?, video?

  4. #14
    Team Member zul8tr's Avatar
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    Quote Originally Posted by Ron Hill View Post
    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!
    Also true with the Merc 25ss with surface gap plugs poor plug for racing. We racers quickly found the projecting center cold Champ L61Y gapped plug with cut back ground electrode (Champ made them that way) And with the CD ignition could gap at 0.050 and beyond and read them. I indexed them as well to the intake ports. This made a big difference with the 25ss in the circuit racing.
    " Three may keep a secret if two of them are dead" Ben Franklin
    " ------- well Doctor what have we got a Republic or Monarchy? A Republic he replies if you can keep it"
    Benjamin Franklin, 1787 Constitutional Convention, as recorded by signer James McHenry's in his diary at the Library of Congress

    Location: SW Orlando, Fl

  5. #15
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    Quote Originally Posted by ice_spy View Post
    It would be great if anyone has any information on the Mercury 402x 35ss? NFL crypto betting Surely all the 44xs guys back in the day, https://www.viberate.com/music-analytics/may have some info about this class and motor? . This would be a great place to include this Mercury outboard's history on BRF
    indeed looking for info on the Mercury 402x 35ss, especially from the 44xs folks. Sharing its history on BRF would be awesome!

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