1985/05/27 Caterpillar

All Caterpillar Engines

SUPPLEMENT: 06/24/85

SERVICE MAGAZINE, MAY 27, 1985, PAGE 7. In the article "Use Caterpillar 6V50 Engine Timing Indicator For Accurate Readings" reason number one appeared incorrectly. It should read: The 6V7910 Injection Transducer can determine the point of injection within ± .2° by measuring the actual pressure inside the fuel line (something that clamp-on units cannot do).

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We have received a number of inquiries from dealers and field representatives about the use of clamp-on timing indicators on Caterpillar diesel engines. We have evaluated two competitive units and compared their operation to the Caterpillar 6V50 Engine Timing Indicator, part of the 6V3100 Timing Indicator Group. The results of our tests indicate that clamp-on timing units operate erratically, and, at best, their readings are quite inaccurate when compared to the Caterpillar 6V3100 Timing Indicator Group.

Some of the reasons for this are:

1. The 6V7910 Injection Transducer can determine the point of injection within ± 2° by measuring the actual pressure inside the fuel line (something that clamp-on units cannot do).

2. All diesel engines have a fixed time delay from the time the fuel leaves the fuel injection pump until it reaches the fuel injection nozzle. This fuel line timing delay can vary between 6° and 11° and is dependent on line dynamics such as length, diameter, material, pressure and engine RPM. These factors must be taken into account when making timing measurements. This delay is automatically taken into account in the circuitry of the Engine Timing Indicator when the 6V7910 Injection Transducer is correctly installed at the injection pump. Published timing specifications for Caterpillar engines are based on reading the timing at the injection pump.

In the clamp-on timing units that we tested, the measured point of injection varied depending on where the pickup was fastened to the fuel line, the clamping force, the RPM of the engine, the residual fuel line pressure, and the fuel line pressure at which the pickup sensed injection. These factors, as well as the delay due to the fuel line length, were not taken into account by the unit and had to be compensated for by an adjustable offset. This means that only relative timing and not absolute readings could be obtained.

3. Clamp-on timing unit readings are very susceptible to normal fuel line vibration and shock produced by both the engine and high pressure fuel injection pumps. This interference caused the timing readings to be erratic.

Using Clamp-On Pickups For RPM Measurements

The 6V2100 Multitach uses a clamp-on 6V6114 Fuel Line Pickup to count the number of fuel pulses per minute to determine RPM. For this type of operation, the clamp-on pickup is well suited because the number of fuel pulses per minute is all that is required to calculate engine speed.

The clamp-on pickup for the 6V2100 Multitach was designed so that it could not be used on the 6V50 Timing Indicator in place of the 6V7910 Injection Transducer.