KEY-GEAR 4N4391 - Caterpillar

System Operation
Use this procedure to calibrate the overspeed of the engine speed switch (ESS). Perform this procedure when the ESS is replaced or when calibration is necessary. The engine overspeed is a adjustable setting. Typically, the setting is 118 percent of rated speed. Engine overspeed prevents the engine from running at a speed that could cause damage to the engine. A overspeed condition causes the ESS to energize the normally closed contacts of relay "SR1". This opens the normally closed contacts of relay "SR1". The fuel shutoff solenoid is de-energized and the engine shuts down. A overspeed lamp is provided on the ESS. A overspeed event has occurred when the overspeed lamp is on. The "RESET" button on the ESS will de-energize the overspeed lamp. Pressing the "RESET" button also returns power to the fuel shutoff solenoid.
Illustration 1 g01633296
Table 1
Engine Information    Overspeed Setting
"(Minimum - Maximum)"    75% Overspeed Setting
"(Minimum - Maximum)"    Setting for the Crank Termination
"(Minimum - Maximum)"    
Engine Model    Number Of Teeth On Flywheel    Typical Rated Engine Speed (RPM)    Engine Speed
Set at 118% of rated speed    Magnetic Pickup Frequency (Hz)    Engine Speed (RPM)    Magnetic Pickup Frequency (Hz)    Engine Speed (RPM)    Magnetic Pickup Frequency (Hz)    
3412     136     1200     1416
(1409-1423)     3210
(3194-3226)     1062
(1051-1094)     2407
(2383-2479)     400
(386-406)     907
(875-920)    
1500 1770
(1761-1779)     4012
(3992-4032)     1327
(1314-1367)     3009
(2979-3099)    
1800 2124
(2113-2135)     4814
(4790-4838)     1593
(1577-1641)     3610
(3575-3719)    Set the Approximate 75 Percent Overspeed with the Engine RPM
Remove the lockwire and the seal from the access hole for the overspeed of the engine speed switch.
Use a screwdriver to lightly turn the screw for the overspeed of the engine speed switch. Turn the screw twenty times in the clockwise direction.
Start and operate the engine at 75 percent of the desired overspeed setting.
Press the button and hold the "75% Verify" button on the ESS.
Slowly rotate the overspeed adjustment screw in the counterclockwise direction.
Rotate the overspeed adjustment screw until the overspeed lamp illuminates. Note: This is the approximate overspeed setting.Adjust The 75 Percent Overspeed Setting
Momentarily press the "RESET" button on the ESS.
Restart the engine.
Operate the engine at 75 percent of the desired overspeed setting minus 100 RPM.
Press the "75% VERIFY" button.
Release the "75% VERIFY" button.
Increase the engine speed by 10 rpm.
Press the "75% VERIFY" button.
Continue increasing the engine speed in 10 rpm increments until the overspeed lamp illuminates.Use a Signal Generator to Verify the Overspeed Setting
Turn the engine control switch to the OFF position.
Disconnect the engine speed input at ESS terminal 3 and terminal 4.
Connect a signal generator to ESS terminal 3 and terminal 4. Use 4C-6534 Adapter Harness for the connection.
Turn the engine control switch to the ON position.
Slowly increase the frequency. Monitor the overspeed lamp. Record the frequency that causes the overspeed lamp to illuminate. Note: The engine overspeed lamp should illuminate when the frequency input is within the range in table 1.