- Caterpillar Products:Machine Engines All 3500 Series
- Caterpillar Products: 3500 Family Generator Sets and Power Modules
- Engine: All 3500 Engines
- Caterpillar Products: 3500 Family Generator Sets and Power Modules
Introduction
Do not perform any procedure in this Special Instruction until you have read and understood the information.
Using these instructions can help detect a single cylinder with excessive pressure blowing past the piston rings.
The blowby can be due to piston rings that are worn or broken. The blowby can also be due to worn or damaged cylinder liners.
The common materials that are needed for the testing can be obtained in most shops.
This test uses the crankcase breathers or T-hoses, where all venting locations are fitted with caps or plugs.
One plug is drilled to provide restriction and amplification of the pressure signal.
One is fitted with a 1/8 inch hose barb fitting and a hose that is routed to a manometer.
All other breathers are capped off.
A manometer is used with the cylinder cutout function of Caterpillar Electronic Technician (ET) to determine crankcase pressure changes associated with individual cylinders.
A torque converter load is maintained on the engine during the test in order to maintain a small load on the engine. The load enables all the injectors to have similar injection duration so that failed cylinder can be found more easily.
Ensure that there are no other leak paths for exhaust gas to escape the crankcase in order to perform the test.
Note: Oil filter differential pressure typically runs between 2 and 4 PSI at coolant temperatures above 77° C (170° F). Excessive blowby is suspected If oil filter differential pressure alarms are present or the filter differential pressure exceeds 5 PS.
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Do not operate or work on this machine unless you have read and understand the instructions and warnings in the Operation and Maintenance Manual. Failure to follow the instructions or heed the warnings could result in injury or death. Contact your Caterpillar dealer for replacement manuals. Proper care is your responsibility. |
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Required Test Materials
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| Illustration 1 | g03251500 |
(1) 1/8 inch hose (2) Hose clamp (3) 1/8 inch hose barb fitting in a plug or cap (4) Plug or cap with drilled hole for restriction and amplification (5) Manometer | |
| Required Materials | |
| Material | Comment |
| 3 ABS plastic plugs 1-1/2 inch inner diameter and 2-1/4 inch outer diameter Or Six similar caps |
The plugs or caps are used to seal off the breathers. Install a threaded fitting into one plug or cap, enabling installation of a 1/8 inch hose barb fitting (3) . Drill a 1/2 inch hole into one plug or cap (4). A 1/2 inch hole is a good starting place. Having a few different caps with 3/8, 1/2, and 3/4 inch orifices will allow the restriction to be varied as necessary. Different sizes can help produce 4 to 10 inches H2O at the beginning of the test. The holes in the plugs or caps provide restriction and amplify the signal to the manometer. A smaller hole increases the restriction (pressure) and therefore increases the amplification. Too little or too much amplification will make cylinders with more blowby difficult to find. A variable sized orifice can be fabricated by inserting a ball valve into the hole. The ball valve can be set to the desired restriction and resulting amplification at the beginning of the test. Do not alter the valve throughout the duration of the testing. Having different sizes that can reduce the amplification can be helpful with engines that have higher blowby. |
| 3 to 6 hose clamps | Clamps (2) secure the plugs or caps onto the breathers. |
| 1/8 inch rubber hose long enough to route from the engine to the engine control. Use hose that resists kinks. | Hose (1) will convey pressure changes to the manometer. |
| Digital manometer with a resolution of 0.01 inches H2O | Manometer (5) will measure pressure changes. |
| Personal computer with Caterpillar Electronic Technician (ET) software | Cat ET will be used to perform the cylinder cutout test. |
Install the Test Materials
- Install the plug or cap with the 1/2 inch orifice (1) into the outlet of one of the crankcase breathers (2). The preferred location is nearer to the engine control. Alternatively, install the plug or cap into the tee hose (3) for a pair of breathers.
The plug provides restriction and amplifies the signal to the manometer.
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| Illustration 2 | g03251555 |
(1) Plug with the orifice hole | |
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| Illustration 3 | g03251519 |
Alternative locations for the plugs (2) Outlet of the breather (3) Outlet of the tee | |
- Install the plug or cap with the 1/8 inch hose barb fitting (4) into another breather or tee hose. The preferred location is nearer to the engine control.
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| Illustration 4 | g03251546 |
(4) Plug with fitting for the 1/8 inch hose | |
- Connect the rubber hose to the fitting. Route the hose to the manometer in the cab. Approximately 15 feet of rubber hose is needed to connect the fitting to the manometer.
- Block the remaining breathers or tee hoses with solid plugs or caps (5), preferably on the right-hand side of the engine.
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| Illustration 5 | g03251557 |
(5) Solid plug | |
- Establish communication with Cat ET and the engine ECM.
Perform the Test
- Operate the engine until a temperature of at least 77° C (170° F) is achieved.
Note: In cold ambient temperatures the radiator may require a tarp to restrict air flow across the radiator in order to maintain coolant temperatures at or above 77° C (170° F).
- Maintain a small load on the engine at low idle to help keep the operating temperature above 77° C (170° F) during the test. For example on a 793D, operate the engine at idle (700 RPM), lock the brakes, chock the wheels, and put the truck into first gear.
- Observe the manometer and allow the crankcase pressure to stabilize. Record the pressure reading from the manometer before each cylinder is cut out.
- Perform a single cylinder cutout test for each cylinder. Closely watch for the change in crankcase pressure. Record the pressure reading from the manometer when a stabilized value is reached.
Note: Make sure to allow the pressure to stabilize for each reading.
Note: Under ideal conditions, the crankcase pressure should be between 4 and 10 inches H2O. If the crankcase pressure is higher or lower than 4 to 10 inches H2O, adjust the orifice size.
- Repower the injector for each cylinder. Closely watch for the change in crankcase pressure. Record the pressure reading from the manometer when a stabilized value is reached.
Note: The crankcase pressure should return to approximately the same value taken before the cylinder was cut out. If the engine changed load during the test due to cycling parasitic load, rerun the test on that cylinder.
Analyzing the Results
The value for the blowby for each cylinder is obtained by subtracting the stabilized reading taken during each cut out cylinder from the reference value. The reference value is taken just before each cylinder is cut out. When repowering the injector the crankcase pressure should return to approximately the same stabilized value, duplicating the same change in blowby.
Example Analysis
The example in Table 2 only uses four cylinders. For an actual test, values for all of the cylinders are used.
| Cylinder 1 | Reference Value | 8.32 in H2O |
| Measured Value by cutting injector 1 | 7.52 in H2O | |
| Measured Value when repowering injector 1 | 8.41 in H2O | |
| Cylinder 8 | Reference Value | 8.52 in H2O |
| Measured Value by cutting injector 8 | 8.63 in H2O | |
| Measured Value when repowering injector 8 | 8.46 in H2O | |
| Cylinder 13 | Reference Value | 8.22 in H2O |
| Measured Value by cutting injector 13 | 8.12 in H2O | |
| Measured Value when repowering injector 13 | 8.18 in H2O | |
| Cylinder 16 | Reference Value | 8.89 in H2O |
| Measured Value by cutting injector 16 | 7.89 in H2O | |
| Measured Value when repowering injector 16 | 8.79 in H2O |
| Cylinder 1 blowby contribution | 8.32 - 7.52 = 0.80 in H2O |
| 8.41 - 7.52 = 0.89 in H2O |
Cylinder 1 has excessive blowby or a failed top ring.
| Cylinder 8 blowby contribution | 8.52 - 8.63 = -0.11 in H2O |
| 8.46- 8.63 = -0.17 in H2O |
Cylinder 8 shows an increase in crankcase pressure. This cylinder is fine. The increase in blowby is caused by the transfer of load and increased injector duration to other powered cylinders.
| Cylinder 13 blowby contribution | 8.22 - 8.12 = 0.10 in H2O |
| 8.18 - 8.12 = 0.06 in H2O |
Cylinder 13 shows only a slight drop in crankcase pressure. This cylinder is fine.
| Cylinder 16 blowby contribution | 8.89 - 7.89 = 1.00 in H2O |
| 8.79 - 7.89 = 0.90 in H2O |
Cylinder 16 has excessive blowby or a failed top piston ring.
Recommendations for Inspection
When suspect cylinders are found, perform the leak test in Special Instruction, REHS7138.
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| Illustration 6 | g03316761 |
(1) Exhaust side plug (2) Valve cover hole | |
Alternatively, cylinders can also be inspected with a borescope through the plug on the exhaust side of the cylinder head. Alternatively, the borescope can also be used through the valve cover hole with the respective valves open.
If necessary, visually compare the suspect cylinder/s to a cylinder that tested ok.
Evaluation Worksheet
| Date |
Unit |
Engine hours |
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| Serial number |
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| Coolant temperature (°C) |
rpm |
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| Reference value for the whole engine (in - H2O) | |||
| Oil Filter Differential Pressure at 1800 Rpm (170°F+ Coolant) | Oil Filter Differential Alarms | Yes / No | |
| Cylinder | A. Stabilized Reference in H2O | B. Stabilized Value after Cutout in H2O | C. Stabilized Value after Repower in H2O | Contribution of Cylinder A-B to B-C in H2O |
| 1 | ||||
| 2 | ||||
| 3 | ||||
| 4 | ||||
| 5 | ||||
| 6 | ||||
| 7 | ||||
| 8 | ||||
| 9 | ||||
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| 13 | ||||
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| 16 |