Improved High Idle Display Of The 6V3100 And 8T5300/8T5301 Engine Timing Indicator Groups

All Caterpillar Engines

SUPPLEMENT: 04/20/87
SERVICE MAGAZINE; MARCH 16, 1987; PAGE 12; “Improved High Idle Display Of The 6V3100 And 8T5300/8T5301 Engine Timing Indicator Groups” on all Caterpillar engines. The third sentence of the second paragraph should read, “The second solution is to purge the air from the transducer cavity by filling the cavity with a fluid such as diesel fuel, silicone or glycerin.”

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Unstable readings on the displays of the 6V0050 or 8T5250 Indicators are most likely caused by air trapped in the transducer cavity or tubing. The unstable readings occur at 000 for the RPM display and the DEG readings at low idle. Also, valid rpm readings but unstable DEG readings occur at high idle. Although readings are obtained at high idle, they may not be accurate because the air, acting as a shock absorber, will delay the pressure pulse.

There are two solutions to the problem. One is to purge the air from the transducer cavity by running the engine at maximum governor speed until the speed and DEG readings are steady. The second solution is to purge the air from the transducer cavity by filling the cavity with a nonflammable fluid such as diesel fuel, silicone or glycerin. A simple fill device such as described in the following procedure will correct the unstable display reading.

Procedure For Improving Operation Of Timing Indicator Display
1. Obtain a plastic squeeze bottle having a removal cap and a capacity of 3 ounces or more. Two bottles recommended for this purpose are HYPO-RH200 from Rohm & Hass Co., Philadelphia, PA and Lindy Wormblower which can be obtained at any fishing supply store.

NOTE: If you use the HYPO-RH200 bottle, remove the cap and discard the metal nozzle. Also, use a No. 58 (.0420″) drill to enlarge the hole in the snout of the plastic cap as shown in Illustration 1. The Lindy Wormblower bottle does not require this modification because the hole in the cap is the correct size.

2. Obtain some plastic tubing (teflon, nylon, polyethylene, or equivalent) having an inside diameter of approximately 0.56 mm (.022″) and a wall thickness of 0.25 mm (.010″). Cut the tubing to a length of 89 to 127 mm (3.5 to 5.0″).

3. Insert the tubing into the snout of the plastic cap and pull the tubing partially through the cap. Using a fine point hot soldering iron or a heated nail, flare the end of the tube which extends from the inside of the cap as shown in Illustration 2. Cool the flared end immediately so it does not shrink and return to its original shape. After cooling, pull the tube through the cap until the flared end of the tube contacts the inside opening of the cap.

NOTE: Make sure that the inside and outside of the tube and injection bottle are free of dirt and contaminants which could damage the engine.

4. Squeeze the sides of the bottle, immerse the open tip end of the squeeze bottle in the fluid and fill the bottle with fluid, then secure the cap/tube to the bottle as shown in Illustration 3.

5. Hold the 6V7910 Transducer in an upright position with the injection bottle above it and insert the free end of the tube into the transducer until the end of the tube bumps into the diaphragm of the transducer. See Illustration 4. Squeeze the injection bottle to force the fluid into the transducer cavity until the fluid begins to exit where the tube enters the 5P7435 Adapter. While maintaining the pressure on the injection bottle, slowly withdraw the end of the tube from the transducer adapter. This will ensure that the fluid fills the cavity previously occupied by the tube and the air.

6. Keep the tube end of the transducer in an upright position until it is installed in the fuel line. After installation, run the engine at full throttle for eight to twelve minutes to allow all the components to reach normal operating temperature and to purge any remaining air from the transducer cavity.

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