1982/01/20 Caterpillar


Improvements And Test Procedures For Hydramechanical Shutoffs

Usage:


D379 (68B5682-Up),
D398 (66B7444-Up),
D399 (35B4702-Up) Industrial Engines;
D379 (34Z478-Up),
D398 (35Z507-Up),
D399 (36Z469-Up) Generator Set Engines So Equipped

Several improvements have been made to the hydramechanical shutoffs for the above models. These improvements were made for better, more positive shutoff operation and longer component service life. A complete list and explanation of the changes which have been made is given in the topic "Shutoff Improvements".

To make sure the shutoff operates correctly and will stop the engine when necessary, test operation at specific intervals is very important. This is the reason for the recommendation in Operation And Maintenance Guides to test the shutoff operation every 500 SMU (Service Meter Units). The topic "Test Procedures" tells how to make the regular maintenance test, and how to check specific circuits and components for correct operation. An important component to check is the drive coupling, because a failure of the coupling will prevent operation of the complete system. The drive coupling test can be made during normal engine operation under full load conditions; it is not necessary to slow down or stop the engine for this test.

Shutoff Improvements

Air Inlet Shutoff Group

1. A new 5N8963 Cylinder (Hydraulic) is used in place of the former 5N3089 Cylinder. In comparison with earlier 5N3089 Cylinders, these improvements have been made:
... A different spring is used in the new cylinder, and in later 5N3089 Cylinders. The new spring is cadmium plated (has a layer of cadmium) to prevent rust. With the former spring, particles of rust fell from the spring to the surface of the seal and caused seal damage. Later 5N3089 Cylinders that use the new spring have an identification mark which is a square with a letter N or later letter inside the square.
... The head of the new cylinder is both longer and larger in diameter than the head of earlier 5N3089 Cylinders. Later 5N3089 Cylinders have a head which is larger in diameter, but not longer. See Illustration I. The larger head diameter prevents possible contact between fitting connections and the cylinder plunger, which can prevent operation of the cylinder. This contact was possible in some earlier cylinders, if fittings were tightened too tightly. The longer head used on the new cylinder gives more clearance so the fittings can be removed or installed without removal of the cylinder from the mounting flange. Also, the increased clearance makes it easier to remove or install the flange bolts.


Illustration 1. Air inlet shutoff cylinders.

2. A new 5N9202 Flange is used in place of the former 5N3084 Flange, which is canceled. The new flange is 6.00 mm (.236") thick in comparison with the 3.00 mm (.118") thickness of the former flange, and has a machined groove for an O-ring seal (see paragraph "3", which follows, and Illustration 2). The thicker flange gives a more rigid mounting for the hydraulic cylinder. Formerly, it was possible for distortion of the flange to prevent free movement of the cylinder plunger. In addition to the increased thickness, later 5N9202 Flanges are made of die cast aluminum. Earlier 5N9202 Flanges and the former 5N3084 Flanges were made of steel plate. For replacement of a former 5N3084 Flange, use the new 5N9202 Flange plus one 5N8963 Cylinder and one 3P5859 Seal.


Illustration 2. New and former mounting flanges for air inlet shutoff cylinder.

3. A new 3P5859 O-Ring Seal is used in place of the former 5N8330 Gasket between the new cylinder flange and the shutoff housing. This will also make the cylinder mounting more rigid (see paragraph "2"). Formerly, it was possible for compression of the soft gasket to cause distortion of the cylinder mounting flange and/or wrong alignment of the cylinder. The new seal, flange and cylinder must be used together.

Control Shutoff Group

Later control shutoff groups operate with a pressure of 760 kPa (110 psi). Earlier groups operate at a pressure of 450 kPa (65 psi).

An earlier article told about a new 5N8227 Gasket used in place of the former 5N3199 Gasket (which is canceled) in later control shutoff groups (760 kPa [110 psi]). The new gasket has separate openings for the rack cylinder passage and the oil drain passage next to it. The former gasket, used in earlier shutoff groups, (450 kPa [65 psi]), had a single opening large enough for both passages, because both were drain passages in the earlier groups. See Illustration 3. When a former gasket is installed in a later control shutoff group, the single opening permits an internal (inside) leakage of oil from the rack cylinder circuit to the drain passage. This can lower the pressure in the circuit enough to prevent positive operation of the rack shutoff in some conditions.


Illustration 3. New and former gaskets used in control shutoff group.

During the initial (first) production (construction) of the 760 kPa (110 psi) groups, the former 5N3199 Gasket was used. Identification of these groups which have the former gasket can be made by the code marks on the identification plate which is on the hydramechanical shutoff. A change has been made to this code since introduction of the 760 kPa (110 psi) groups. A 1E15 code was used first and then changed to a number sequence code. All 760 kPa (110 psi) groups with the 1E15 code, and those with a number sequence code below 00313 have the former 5N3199 Gasket. If a problem is found with operation of the rack shutoff on one of these groups, remove the 5N3199 Gasket and install the new 5N8227 Gasket.

Rack Shutoff Group

A new 9N4053 Spring is used in place of the former 5N5758 Spring in the rack shutoff group. The new spring is approximately 57.2 mm (2.25") long and the former spring is approximately 106.7 mm (4.20") long. The new spring has less force than the former spring, and permits more positive operation of the cylinder. See Illustration 4. With the former spring, oscillation of the cylinder piston was possible during tests for low oil pressure or emergency manual shutoff conditions (when the red knob is pulled while the air inlet shutoffs are held or fastened open). If this oscillation is found during test procedures, the spring can be checked as a possible cause. If replacement of the spring is made and oscillation does not stop, a check valve may be needed. See the November 3, 1980 Service Magazine, page 5.


Illustration 4. New and former springs used in fuel rack shutoff.

Test Procedures

All the tests shown in the paragraphs which follow are normally made at low idle engine rpm. The tests can be made at any engine rpm, but tests at a higher rpm are not necessary. If the shutoff operates correctly at low idle rpm, the systems will operate faster at a higher rpm.

While most of the tests make it necessary to stop the engine, the drive coupling, override valve and override actuator (palm valve) tests can be made during engine operation under full load conditions. This makes it possible to check the drive coupling when conditions do not permit the engine to be stopped. Under these conditions, the recommendation is to make this test every 500 SMU as a minimum check because a coupling failure will prevent operation of all control circuits.

Illustration 5 shows the primary components and circuits, and can be used as a reference during test procedures. Illustrations 6 and 7 show the locations of shutoff components on the engine.


Illustration 5. Schematic diagram for control shutoff.

Regular Maintenance Test (Every 500 SMU)

This test must be made every 500 SMU to be sure the hydramechanical shutoff operates correctly. To make the test, run the engine and pull the red emergency knob. This activates the control, and the engine must stop. If the engine does not stop, a repair must be made so the engine will have protection during operation. After the engine stops, check the air inlet shutoff valves to be sure both valves are completely closed, then open both valves.


NOTICE

Be sure both air inlet shutoff valves (one on each side of the engine) are open before the engine is started. Both valves must be open to prevent possible engine damage.


Drive Coupling Test

Run the engine and loosen the line nut one-half to three-fourths of a turn on the fitting for the oil supply line to the diverter valve. See Item 3 in Illustration 5. Put a shop towel around the line and fitting for protection from oil spray (fluid under pressure) and, if necessary, move the tube a little to be sure it is loose from the fitting. Any flow of oil from the loosened connection is an indication of rotation of the input shaft of the hydramechanical shutoff. Tighten the line nut.

Override Valve Test

Run the engine and disconnect the drain line from the override valve. See Item 5 in Illustration 5. Any flow of oil from this line is an indication of failure of either the override valve or override actuator. To find which valve has the failure, disconnect the air line between the override valve and override actuator. If the oil flow from the drain line stops, the failure is in the override actuator. If the oil flow does not stop, the failure is in the override valve.

Air Inlet Shutoff Valve Test

Run the engine at low idle rpm, and pull the red emergency knob. Both air inlet valves must close, and stop the engine. See Illustrations 6 and 7 for locations of parts.


NOTICE

After this test, both air inlet valves (one on each side of the engine) must be opened before the engine is started. If the engine is started while either valve is closed, the engine can be damaged.


Fuel Rack Shutoff Test

Fasten both air inlet valves in the open position. The valves can be fastened with wire, or held open manually by two persons. Run the engine at low idle rpm, and pull the red emergency knob. With the air inlet valves open, the fuel rack shutoff must stop the engine. If the engine does not stop, it is possible that the control shutoff group has an earlier gasket which permits leakage of oil from the rack cylinder circuit. See the Paragraph "Control Shutoff Groups" in the topic "Shutoff Improvements". If this is the problem, install a new 5N8227 Gasket.


Illustration 6. Air inlet shutoff valve on left side of engine.


Illustration 7. Shutoff components on right side of engine.

Remove the wire from the air inlet valves when the test is complete.

Low Oil Pressure Shutoff Test

At the control group, disconnect the oil supply line which is connected between the control and the thermostatic pilot valve in the cooling system. See Illustration 5. In place of this line, connect a 3N4847 Hose Assembly to the control. At the other end of the hose, install a 7D5363 Connector and 3R3837 Valve. Put the end of the hose with the valve in a container (reservoir) large enough for approximately one-half liter (one pint) of oil which will be drained. With the valve closed, start the engine and let it run at low idle rpm. Normal engine operation can be expected. Open the 3R3837 Valve to drain oil into the container. This lowers the engine oil pressure in the control circuit to activate the low oil pressure shutoff, and the fuel rack shutoff cylinder must stop the engine. Only the rack cylinder is activated by this circuit; the air inlet shutoff valves do not close.

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