Cummins N14 – Injection Timing – General Information

The injection timing is the relative measurement of the distance remaining between the injector plunger and the injector cup when the piston is 5.161 mm [0.2032-inch], or 19 degrees before top dead center (TDC) on the compression stroke.
Injector timing is expressed by the amount of push tube travel remaining.

The injection timing code appears on the engine dataplate. Codes are alphabetic letters that relate to a numerical specification.
Specifications can be found in the Control Parts List (CPL) Manual, Bulletin No. 3379133.

Advanced timing (1) means the fuel is injected earlier into the cylinder during the compression stroke. Retarded timing (2) means the fuel injection occurs closer to TDC in the cylinder.

The amount of push rod travel determines the time of fuel injection in relation to the piston position.
A low numerical value of the push rod travel remaining indicates a greater degree of advanced (1) or fast timing.
A high numerical value of the push rod travel remaining indicates a greater degree of retarded (2) or slow timing.

Injection timing changes are accomplished by advancing (1) or retarding (2) the cam follower action in relation to the piston position.
This is accomplished by changing the orientation of the camshaft lobe to the cam follower using different cam follower gasket thicknesses or offset camshaft gear keys.

NOTE: Gear train timing (index mark alignment) always remains the same.

NOTE: The injection timing check is a measurement which determines the injector push rod travel in relation to the piston travel. Due to normal parts tolerances, it is necessary to check one cylinder for each cam follower housing.

Timing Tool Installation
Install the piston plunger rod in the injector bore of the No. 1 cylinder.

NOTE: Make sure the plunger is centered and on top of the piston.

Align the swivel bracket with the injector clamp capscrew hole. Install the 6-inch swivel bracket capscrew. Tighten the capscrew finger tight.
Position the push rod plunger rod near the push rod.

Tighten the swivel bracket capscrew enough to hold the timing tool rigid. Make sure the piston plunger post is clamped squarely to the cylinder head.

Align the plunger rod (1) and the injector push rod (3) with each other, and parallel to the plunger rod.

NOTE: Tighten the clamp handle (2) after the plunger rod is aligned with the injector push rod.

Loosen the support bracket (4) and slide the bracket down until the plunger rod (1) engages the injector push rod (3).

NOTE: The support bracket must be aligned with the vertical line on the clamp handle bracket. The push rod (3) must be vertically aligned with the plunger rod (1).

Compress the plunger rod tension spring approximately 12.7 mm [0.50-inch], and tighten the support bracket.

Determine the piston top dead center (TDC) on the compression stroke by rotating the crankshaft in the direction of engine rotation (clockwise) until the piston plunger reaches its uppermost position.

NOTE: Use only the crankshaft to rotate the engine. The use of the gears will result in false measurements. Gear lash must be closed up in the direction of normal rotation (crankshaft clockwise ).

NOTE: The timing tool indicator needles will both start to move in the same direction of rotation as the piston approaches TDC if the cylinder is on the compression stroke. If both needles do not move in the same direction, rotate the engine one complete revolution in the same direction of rotation.
The next frames explain proper orientation and measurement with the dial indicators.

Put the piston travel dial indicator over the plunger rod with the contact tip in the center of the piston plunger rod.
Lower the indicator to within 0.63 mm [0.025-inch] of the fully compressed position.
Tighten the thumbscrew to hold the gauge in position.

Rotate the crankshaft back and forth to make sure the piston is precisely at top dead center (TDC) on the compression stroke.

NOTE: Always set the dial indicator at ‘‘0’’ (zero) at TDC with the crankshaft having just been rotated in the direction of normal rotation (clockwise) to reduce the timing errors due to gear backlash.

NOTE: TDC is indicated by the maximum clockwise position of the piston travel indicator pointer.

Set the dial indicator at ‘‘0’’ (zero). Lock the indicator face with the thumbscrew.

Rotate the crankshaft in the direction of engine rotation (clockwise ) to 90 degrees after top dead center (ATDC).

NOTE: The piston travel plunger will be at the ‘‘NH/NT 90-degree’’ mark on the timing tool.

Put the push rod travel dial indicator in the center of the injector push rod plunger. Lower the indicator to within 0.63 mm [0.025-inch] of fully compressed position, and tighten the thumbscrew to hold the indicator in position.

Set the dial indicator at ‘‘0’’ (zero). Lock the indicator face with the thumbscrew.

Rotate the crankshaft in the opposite direction of engine rotation (counterclockwise ) through TDC to 45 degrees before top dead center (BTDC).

NOTE: This step is necessary to remove the gear train lash and to provide more accurate indicator readings.

Observe the dial indicator readings prior to crankshaft rotation to assist in later determining BTDC piston setting and timing reading.

NOTE: If the crankshaft is rotated beyond the -5.161 mm [-0.2032-inch] position, the crankshaft must be rotated counterclockwise back to 45 degrees BTDC. Repeat the following step.

Rotate the crankshaft slowly in the direction of engine rotation (clockwise ) until a reading of -5.161 mm [-0.2032-inch] BTDC is reached on the piston travel dial indicator.

Compare the reading of the injector push rod travel indicator to the specification listed for the timing code.

NOTE: The push rod travel indicator is read in a counterclockwise direction from ‘‘0’’ (zero). The total amount of travel represents the injection timing value.

If the injection timing is not within the specified limits, check the following:
1. Is the timing tool correctly installed?
2. Are the dial indicators correctly adjusted?
3. Has the crankshaft been rotated in the correct direction and timing sequence?
4. Are the cam follower housing capscrews correctly tightened?
5. Are the crankshaft and camshaft gears in proper alignment?

NOTE: To verify the correct injection timing for a particular engine, check the injection timing code on the engine dataplate. To acquire the timing specifications, refer to the Control Parts List (CPL) Manual, Bulletin No. 3379133.

If the indicator reading is higher than the specification,the timing is retarded (2).
If the indicator reading is lower than the specification, the timing is advanced (1).

NOTE: The injection timing can be changed by removing the cam follower housing and by increasing or decreasing the gasket thickness. Each 0.18 mm [0.007-inch] of gasket thickness affects injection timing by approximately 0.05 mm [0.002-inch] indicator travel.

NOTE: Gaskets are available in the following nominal thicknesses:
1. 0.18 mm [0.007-inch].
2. 0.43 mm [0.017-inch].
3. 0.43 mm [0.017-inch] (Print-O-Seal*).
4. 0.56 mm [0.022-inch].
5. 0.76 mm [0.030-inch].
*One Print-O-Seal gasket must be used for each cam follower housing.

Increase the gasket thickness to advance the injection timing (Add = Advance).

Decrease the gasket thickness to retard the injection timing (Remove = Retard).

The accompanying chart lists the different cam follower housing gaskets, the gasket thickness, and approximate change in push rod travel at 19 degrees BTDC 0.2032 inch piston travel.

NOTE: The Print-O-Seal gasket (1) must be against the cylinder block with the sealing bead toward the cam follower housing. The minimum amount of gasket stack-up thickness which can be used is 0.43 mm [0.017-inch] (one Print-O-Seal gasket). The maximum gasket stack-up thickness allowed is
2.03 mm [0.080-inch].

If you can not correct the injection timing by increasing or decreasing the thickness of the cam follower housing gaskets (1), an offset camshaft key (2) must be installed.
The timing code specifies the required camshaft key. An offset key can be required initially.

After completing the injection timing check on cylinder No. 1, check the injection timing on cylinders No. 5 and No. 3.

15. October 2020 by samuel
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