COUPLING AS- 3971961 - Caterpillar

Illustration 1. Fuel System Data from "Fuel Setting And Related Information " microfiche 0T4858.
Illustration 2. Dynamic timing tolerance for 0T4858.Example 2 uses Fuel System Data from 0T4442. See Illustration 3. This is an example of an engine equipped with a timing advance mechanism. This dynamic timing tolerance will have three windows instead of two as in Example 1. Four data points are located and connected, as in Example 1, for low idle rpm, start rpm and stop rpm. This forms three windows. The extreme limits of all the windows are then connected to form the dynamic timing tolerance as shown in Illustration 4. The slope of the lines, from the start window to the low idle window, is the result of port effect. The slope of the lines, connecting the low idle window and the stop window, is the result of port effect and the timing advance mechanism spring rate. The scope of the lines can not be changed unless a different spring is installed in the timing advance mechanism. Only the points where the slope starts and stops can be adjusted.
Illustration 3. Fuel System Data from "Fuel Setting and Related Information microfiche 0T4442.If the measured fuel injection timing passes through each window of the dynamic timing tolerance, and does not fall outside the lines connecting the windows, no adjustment or repair is required. If measured timing is outside the Low Idle or Start RPM dynamic timing tolerance window an appropriate adjustment to static timing will be necessary to bring the measured timing back within tolerance. If the engine has acceptable Start RPM advance, but incorrect Stop RPM advance (outside Stop RPM window), an adjustment or repair of the timing advance mechanism is required. The change in slope of the measured dynamic timing indicates the start or stop of timing advance and should occur within the appropriate window. If not, an adjustment or repair of the advance mechanism is required. Consult the appropriate service manual for the repair or adjustment procedure necessary to achieve the correct dynamic timing.
Illustration 4. Dynamic timing tolerance for 0T4442.