1977/06/29 Caterpillar

Because of the nature of the information in this article, it is not written in Caterpillar Fundamental English.

Here is an article of direct interest to servicemen who work on Caterpillar fuel systems. Please test all fuel injection nozzles (capsule-type or pencil-type) removed from any engines before a new nozzle is used as a replacement. If the removed nozzle tests satisfactory, use it again.

Tests by Caterpillar Tractor Co., with the 5P4150 Nozzle Tester Group and in engines, have shown that many used nozzles returned to Caterpillar as defective did not need replacement. The 5P4150 Nozzle Tester Group or the 8S2242 Nozzle Tester Group with the 5P4149 Conversion Group must be used to make a test on all nozzles removed from an engine, unless the nozzle shows damage. The 5P4150 Tester is the only tester that can be used for 9L6884 Nozzles in 3400 Series Direct Injection Engines. These tools and their Special Instruction Form FM055225-03 were made available to provide a quick, accurate method of testing all types of fuel nozzles.

Be sure you are thoroughly familiar with the correct procedures and specifications in the Special Instructions. For example, one Step sometimes overlooked in testing the 9L6969 Pencil-type Nozzles is the failure to remove the cap from the nozzle. This must be done to prevent a hydraulic lock when the nozzle is checked with the tester.

Nozzle tester for pencil-type nozzles-8S2242 Nozzle Tester Group shown.

If you make tests on large quantities of pencil-type or capsule-type nozzles, use two testers. Use a tester for each nozzle type. This prevents leakage by eliminating repetitive tightening and loosening of the line and adapter on the tester. The former 8S2242 Group can be used for all nozzles in 1100, 3100, and 3208 Engines

Tips For More Exact Tests

... You do not need to make tests on new capsule nozzles, but if you do make a test, install the nozzle in a precombustion chamber and tighten to the correct torque. Remove the nozzle and make the test. The tightening forces can seal the internal parts the same as if the nozzle were installed in the engine.

... Do not make tests on hot nozzles. High temperatures reduce the fluid viscosity and cause too much "leak down" (pressure drop).

... If the calibrating oils listed in the Special Instruction are not available, use a diesel fuel in the API range of 35 to 41 at 60°F (16°C). With diesel fuel, the specifications for PC (precombustion chamber) capsule nozzles are:

Used PC Nozzles (With Diesel Fuel)

Pressure to Open Valve (VOP):

400-750 psi (2750-5200 kPa)

Rate of Leakage:

With a pressure of 300 psi (2050 kPa), pressure reading must not be less than 100 psi (690 kPa) after 30 seconds. Therefore, permissible pressure drop is 200 psi (1380 kPa).

New PC Nozzles (With Diesel Fuel)

Pressure to Open Valve (VOP):

685-750 psi (4720-5200 kPa)

Rate of Leakage:

With a pressure of 600 psi (4150 kPa), pressure reading must not be less than 200 psi (1380 kPa) after 30 seconds. Therefore, permissible pressure drop is 400 psi (2750 kPa).

Test specifications with different test fluids are not known for the direct injection nozzles.