PLATE 8R7912 - Caterpillar

All Marine, Industrial, Generator Set Engines Except 3600 Family Of EnginesReference: Service Magazine; October 21, 1985; Page 4, "Engine Shuts Down Immediately After Start-up". Service Magazine; February 13, 1984; Page 5, "Engine Will Not Restart Immediately After It Has Been Shutdown".Description of Change: The above engines have a 4W8471 Relay. This is a 70 second time delay relay (TDR) to make sure the engine stops completely when it is shutdown. A diode has been added to the circuit connected to the TDR to prevent damage to the TDR from high voltage spikes.Adaptable To: The 5N4988 Diode Assembly can be adapted to only the affected engines previously modified in the field to make it possible to override the 70 second TDR. This field modification has allowed voltage spikes to damage the TDR. Current production does contain a redesigned override feature that prevents damage to the TDR from voltage spikes. The control panel circuits on the earlier engines could have been modified in the field in one of two ways, depending on the design of the circuit. For circuits modified according to the first Reference Article (read Solution B), use Illustration 1. On these engines, the junction box jumper between terminals 27 and 28 has been removed, and terminal 27 has been connected to the output side of the electric starter magnetic switch (solenoid). Simply connect the new diode between 27 and 28 as shown.
Illustration 1. Diode added to engines previously modified according to the Service Magazine of October 21, 1985.For circuits modified according to the second Reference Article, use Illustration 2. Disconnect B- wire at 3 Neg terminal on the TDR. Connect the new diode to the B- wire and to the 3 Neg terminal as shown.
Illustration 2. Diode added to engines previously modified according to the February 13, 1984 Service Magazine.