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How to Adjust Cummins Engine Injectors and Valves

The Cummins engine uses its unique PT fuel system. The injector controls the fuel entering the cylinder. The valve controls the intake and exhaust valves of the engine. At the same time, the adjustment of the injector and the valve are interrelated in the adjustment sequence and method. Only if these two adjustments are properly made can the engine operate normally. Taking the NT(A)855 and KT(A)-1150 engines applied to construction machinery as an example, two methods for adjusting the valve of the injector are introduced.

1. Torque method: The NT (A) 855 engine with a large cam non-stop injector is taken as an example to introduce the torque adjustment method.

Adjustment requirements

Look at Table 1 for the technical requirements for the adjustment of the injectors and valves of the NT(A) 855 engine.

Table 1: Adjustment parameters of injectors and valves for NT(A) 855 engine Oil temperature Injector plunger adjustment torque N.m Valve clearance mm Aluminum rocker chamber Cast iron rocker chamber

Oil temperaturePlunger adjustment torque N.mValve clearance mm
Aluminum rocker chamberCast iron rocker chamberIntake valveExhaust valve

First determine whether the engine uses a cast iron rocker arm chamber or an aluminum rocker arm chamber.

1 Loosen the lock nut of the injector rocker adjustment screw for all cylinders.First confirm whether the engine uses a cast iron rocker arm chamber or an aluminum rocker arm chamber.

2 Twist the engine in the direction of engine rotation (right-handed) so that the mark A or 1-6VS (B or 2-5VS, C or 3-4VS) on the pulley is aligned with the arrow on the gear chamber cover.

3 Check the valve rocker arm of the I and VI cylinders (II and V, III and IV) to which the pulley mark is aligned. The valve of one cylinder must be closed, which is the cylinder that should be adjusted.

4 Adjust the injector plunger. Tighten the injector adjustment screw until the plunger contacts the nozzle cup, then screw in 15° to squeeze out the fuel in the cup; repeat twice to ensure that the fuel in the cup is completely squeezed; remove the adjustment screw ring, use a torque wrench and a screwdriver to tighten the adjusting screw according to the adjustment requirements, and then tighten the lock nut with a torque of 54 ~ 61N.m.

5 Adjust the T-plate so that the gap between the nail plate and the valve spring seat is at least 0.51mm.

6 Adjust the valve gap. Loosen the lock nut, exit the adjustment screw, put it between the rocker arm and the nail platen with the feeler gauge, then screw  in the adjustment screw until the rocker arm just touches the feeler gauge, and then lock the adjustment screw with the torque of 54~61N.m. Tight nut.

7 Continue to turn the engine and adjust the remaining cylinders in the same steps. When applying the torque method adjustment, it should be noted that the valve of the same cylinder should be adjusted immediately after adjusting the injector of one cylinder, but it is not allowed to adjust the valve after adjusting the valve.

2. Thousands of points means that the dial gauge method is a method to adjust the injector plunger stroke to achieve correct adjustment.

The plunger stroke must be adjusted to the specified value. Here, the adjustment of the KT (A)-1150 engine is taken as an example to introduce this method.

(1) Adjustment requirements The adjustment requirements for KT(A)-1150 engine injectors and valves are shown in Tables 2 and 3, respectively.

(2) Adjustment method

1 Twist the engine in the direction of rotation until the mark A on the pulley is aligned with the arrow on the gear chamber. In this position, the valves of the V-cylinder are closed, and the injector plunger of the III-cylinder is at the top of the stroke. If not, the engine crankshaft should be turned 180° and realigned with the arrow. When the engine is turned around, no fan can be used to turn the engine, and a specially designed engine shaft is used. In the process of marking, any mark can be used as a starting point for adjustment, and it is not necessary to start with mark A.

2 Install the adjustment dial gauge correctly onto the rocker arm chamber so that the joint rod contacts the top of the III cylinder injector plunger.

3 Loosen the lock nut of the adjusting screw, screw the adjustied screw, squeeze out the fuel in the oil cup, then exit 1/2 turn, carefully screw it to the bottom to ensure that the injector plunger contacts the bottom of the fuel injector cup. Tighten the adjusting screw too much. Set the dial indicator to zero.

4 Slowly retract the adjustment screw until the dial gauge reads 7.72 mm, then tighten the lock nut.

5 Press the injector plunger to the bottom with a rocker lever to check if the zero adjustment of the dial gauge is correct, then slowly pull the plunger back up and check if the dial gauge reading is within the adjustment requirements. After adjustment, tighten the lock nut with a torque of 41 to 47 N.m and remove the dial gauge.

6 Adjust the III cylinder injector and V cylinder valve; when adjusting the valve, the valve T-plate must be adjusted first. The adjustment gap of the valve is shown in Table 2.

7 After adjusting the III cylinder injector and V cylinder valve, follow the same steps to adjust the remaining cylinders.

Note: When adjusting the injector and valve, using the dial gauge method, never adjust the injector and adjust the valve on the same cylinder. It should be adjusted strictly as per the mark listed in Table 3 and the corresponding cylinder number of the injector and valve.

Table 2: Adjustment parameters of the KT(A)-1150 engine using the dial gauge method

Injector plunger strokeValve clearance
7.72±0.003Intake valveExhaust valve

Table 3: KT(A)-1150 engine injector and valve adjustment position

Turning directionPulley positionAdjust the nozzle cylinder numberAdjusting valve cylinder number
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