855437A 2 Mercury FITTING KIT, Pump Outlet

Introduction
The problem that is identified below does not have a known permanent solution. Until a permanent solution is known, use the solution that is identified below.Problem
The turbochargers surge on some G3520B petroleum engines. This condition occurs mainly in cold ambient conditions below 10° C (50° F). A symptom of turbocharger surge is sudden fluctuations in the manifold air pressure which causes fluctuations in speed. This generally occurs when the engine is being loaded. Also, this generally occurs between 50 percent and 100 percent engine load. Noise from the turbocharger may be present while the turbochargers surge.The turbocharger surge is caused by an increase in the pressure across the turbochargers. An increase in turbocharger boost enables the engine to maintain higher manifold pressures at lower throttle positions. A reduction in the throttle position for a given manifold air pressure reduces the air flow through the compressor side of the turbocharger. When the air flow through the compressor decreases enough, the turbocharger compressor will surge. When the turbocharger surge occurs the air flow through the compressor can reverse. This will result in a sudden drop in manifold air pressure. Also, the speed will become unstable.Solution
When the problem is encountered, the compressor bypass must be adjusted in order to reduce the boost pressure. Perform the procedure in the coldest ambient temperature in the engine's operating range. Use the following procedure to adjust the bypass valve for the turbocharger.
Stop the engine.
Turn the engine control switch to the STOP position.Note: The Electronic Control Module (ECM) and the actuator for the compressor bypass must be powered. This will keep the bypass actuator in position.
Illustration 1 g01735314
(1) Sleeve (2) Coupler (3) Set screw (4) Nut
Mark the location of sleeve (1) on the coupler (2) .
Loosen the set screws (3) on the coupler (2) .Note: The flats on the nut of the valve (4) are 60 degrees from each other. Use the sleeve (1), the nut of the valve (4) and the coupler (2) as a reference.
Illustration 2 g01735402
Flow arrow
Rotate the shaft of the valve in the direction of the flow arrow. Adjust the valve so that there is approximately 15 degrees between the reference mark on the coupler (2) and the sleeve (1). This will slightly open the valve of the compressor. A small adjustment of the valve will have a large effect on the differential pressure of the throttle. If the valve is adjusted too much the throttle will go to the 100 percent position before the engine reaches rated load. This is due to the loss of boost pressure.
Tighten the set screws (3) to 15 1 N m (11 0.7 lb ft).
Restart the engine and attempt to load the engine.
Repeat the procedure increasing the angle of the bypass valve, if the engine surges with a load.
The engine must stabilize for five minutes at full load after the engine loads smoothly.
Adjustments to the exhaust bypass valve can be made if the engine is not capable of full load or the throttle position is greater than 75 percent open at full load. The adjustments can be used to increase the boost and the adjustments can be used to lower the throttle angle. Reduce the angle of the bypass valve if enough turbocharger boost is not gained in order to allow the engine to reach full load capacity through the adjustment of the exhaust bypass valve. Also, reduce the angle of the bypass valve if the throttle remains open greater than 75 percent.
Ensure that the engine is operating at proper emissions.
Record a complete Performance Data Sheet for future reference.Note: The G3520B petroleum engine requires a special rating request for altitudes above 1524 m (5000 ft).