Tools Required
J 26999-30 Compression Gauge Adapter
Cranking speed is critical in order to start a diesel engine, whether
the engine is hot or cold. Some tachometers are not accurate for cranking
speed. The following procedure shows an alternate method of checking cranking
speed or determining the accuracy of a tachometer.
- Screw J 26999-30
into any cylinder
and connect the compression gauge.
- Disconnect the injection pump fuel solenoid lead on the top of
the injection pump.
- Install the digital tachometer to be checked.
- Depress the pressure release valve on the compression gauge.
- With the aid of an assistant, crank the engine for 2 - 3 seconds
to allow the start to reach full speed.
| 5.1. | Without stopping, count the number of puffs at the compression
gauge that occur in the next 10 seconds. |
| 5.2. | Multiply the number of puffs in the 10 seconds
period by 12. The resulting number will be the engine speed. |
The following are examples of counting puffs and measuring them to engine
speed.
| • | 10 seconds = 1/6 of a minute |
| • | 1 puff = Engine speed of 2 |
| • | Engine speed = Number of puffs x 2 x 6 or |
| • | Engine speed = Number of puffs x 12 |
Minimum cranking speed on the 6.5L diesel engine is 100 cold
and 180 hot. The actual cranking speed needed will vary depending on
the condition of the engine compression and the nozzles.
