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Decompressor Mechanism, explained

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  • #1

    Decompressor Mechanism, explained

    I was working on the TL today and thought it might be helpful for some to see how the decompressor mechanism works and offer a few tips.

    The decompressor uses centrifugal force to cause the weighted arm to swing out when the engine is running. A small spring holds it in place when the engine is off or just being turned over by the starter. My thumb is replacing centrifugal force in this photo
    Last edited by Duken4evr; 09-28-2003, 01:09 PM.
    "The reasonable man adapts himself to the world; the unreasonable one persists in trying to adapt the world to himself. Therefore, all progress depends on the unreasonable man." - George Bernard Shaw
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  • #2
    When the lever is not swung out due to spinning forces (while starting the engine) the round side of the pin protrudes above the base circle of the cam, which allows the pin to contact the tappet bucket, which pushes it down, causing the exhaust valve to crack open a bit on the compression stroke during starting.
    Last edited by Duken4evr; 09-28-2003, 01:09 PM.
    "The reasonable man adapts himself to the world; the unreasonable one persists in trying to adapt the world to himself. Therefore, all progress depends on the unreasonable man." - George Bernard Shaw

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    • #3
      When the engine starts, centrifugal force causes the lever to open, this in turn rotates the pin so the flat side milled into the otherwise round pin faces the tappet so no contact is made and the cam operates normally.
      Last edited by Duken4evr; 09-28-2003, 01:11 PM.
      "The reasonable man adapts himself to the world; the unreasonable one persists in trying to adapt the world to himself. Therefore, all progress depends on the unreasonable man." - George Bernard Shaw

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      • #4
        Because of how this setup works, it is important to position the exhaust cams so the pin is not contacting the bucket when checking valve clearance on the 2 valves equiped with the decompressor hardware.

        If you simply line up the cam so the lobe is facing directly away from the bucket (a not unreasonable thing to do, ordinarily) while checking valve clearance, you will get an artificially large reading on the one exhaust valve on each cylinder that has the mechanism. This could cause you to errantly put too thin a shim in and have a two very tight exhaust valves.

        Of course, you can also grind off the rod that mounts the levers and do away with the whole thing pretty easily too
        Last edited by Duken4evr; 09-28-2003, 01:12 PM.
        "The reasonable man adapts himself to the world; the unreasonable one persists in trying to adapt the world to himself. Therefore, all progress depends on the unreasonable man." - George Bernard Shaw

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        • #5
          great explanation

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          • #6
            cool . now go grind it off and explain it all over again
            2002 TLR B/W . Yoshimura bolt on Titanium cans. Yosh box remap. Joe V airbox mod. plug in TRE. 17/41 sprockets. Zero Gravity double bubble screen. fan switch. HyperPro steering damper. Extreme Graphic Top Gun undertail. Ohlins rear shock.

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            • #7
              All the TL's have a decompression device? These work wonders on the deisels at work. I would think a gas engine would have a strong enough spark to start. We use the decompresson lever to heat the cyclinder and get the rings seated before it gets started. Helps out tremendously in the winter.

              Do the TL's need better rings? Mine starts like a damn deisel. But I know all the tricks and such to help cold starts.
              Don't know how it works? Take it apart and find out!

              Pictures

              Here's how it sounds.

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              • #8
                My DRZ400 has the same thing as well. The reason for it is to make the large pistoned TL turn over easier when starting. This theoretically allows Suzuki to get away with a smaller starter and battery than they would have had to spec otherwise, although many have removed the decompressor stuff without problems.

                I would imagine if your batter is in the right stage of being marginally worn out, the bike would start if left stock and would not, due to the higher cranking resistance of full compression, if modified.
                "The reasonable man adapts himself to the world; the unreasonable one persists in trying to adapt the world to himself. Therefore, all progress depends on the unreasonable man." - George Bernard Shaw

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