TURBOCHARGER GP 1458884 - Caterpillar

3116 (4KG, 1SK) Marine EnginesThese engines have an additional Low Idle Adjustment Screw "Buffer Spring Adjustment Screw" on the governor that is used with the standard low idle adjustment to minimize low idle surge or instability. This additional adjustment screw is used ONLY on the 3116 Marine Engines, and is usually referred to as the "Buffer Spring Screw". This is because the screw and related internal spring and other parts are used to "buffer" or dampen the response of the governor at low idle. The larger fuel nozzle orifices in the marine engine injectors and the lower low idle setting make the engine more susceptible to low idle instability.
The "Buffer Spring Adjustment Screw (2) is located on the outboard side of the governor, slightly forward and below the larger core plug in the side of governor housing.
3116 Marine Engine Low Idle Adjustment Procedure
Use a digital photo tachometer to accurately measure the engine low idle rpm. DO NOT use the instrument panel tachometer to set engine low idle. Use this procedure any time the low idle rpm is changed, even slightly.
Location of "Standard" low idle adjustment screw (1) and "Buffer" spring adjustment screw (2).1. Start the engine and allow it to warm up and allow the low idle reading to stabilize. Low idle readings should be taken after snapping the throttle open about (1/3 of its travel), and releasing it quickly. This will help insure the governor control is in its natural low idle position against the standard governor low idle screw (1).2. Turn the "Buffer" spring adjustment screw (2) out (counterclockwise) until there is no further change in low idle rpm. The rpm should drop slightly when screw (2) is turned out.3. Actuate the governor control lever, and then quickly release the lever. Check the low idle rpm. Use the "Standard" low idle adjustment screw (1) to adjust the low idle to 600 10 rpm. Actuate the governor control lever, and then quickly release the lever. Check the low idle rpm. Adjust screw (1) as needed to obtain the 600 10 rpm.4. Slowly turn the "Buffer" spring adjustment screw (2) in (clockwise) until the low idle rpm begins to increase. Continue to turn screw (2) until the low idle rpm is 650 10 rpm. Actuate the governor control lever, and then quickly release the lever. Check the low idle rpm. Adjust screw (2) as needed to obtain the 650 10 rpm. The "Buffer" screw (2) MUST be turned out (counterclockwise) initially, while the low idle is set 50 rpm LESS then the final value with screw (1). Then the "Buffer" screw (2) is used to adjust the low idle rpm upward to the final (specified) low idle rpm. If the "Buffer" screw is used to raise the rpm too much or too little, it does not dampen the movement of the internal governor parts. Low idle instability or surge can be a result.