Indicator cards should be taken under steady conditions when the weather is calm. The load on the engine should be between 85 and 100%. Liaise with the OOW that there is no intended change of course which could vary the load on the engine.
Run the engine at full load for 30 minutes before taking the cards, especially if it has been running at low load in the previous 24 hours. This is to burn off any carbon in the cylinder. Blow through the indicator cocks to prove they are clear and to remove any particles of carbon.
Ensure that the indicator equipment is in good condition and that the piston is free to move in the cylinder. Ensure that the correct spring is fitted.
Fit the pressure sensitive paper to the drum
Before fitting the indicator equipment to each cylinder blow the indicator cock through.
Fit the equipment to the indicator cock. Press the pen against the drum and pull the cord to rotate the drum by hand to draw the atmospheric line.
Unlock the indicator cam drive and drop it onto the cam. Attach the cord to the drive. The drum will now be rotating back and forward in synch with the piston position.
Open the indicator cock fully. Press the pen against the paper and trace out the indicator card. Release the pen and shut the indicator cock. Disconnect the cord from the cam drive. Remove the equipment from the indicator cock and remove the paper with the indicator diagram from the drum.
Record exhaust temperature, fuel rack setting, scavenge pressure and temperature
Repeat for all the engine cylinders.
A set of draw cards should also be taken.
Indicator cards should be taken at regular intervals as part of the planned maintenance for the engine. They should also be taken after any major overhaul of the engine or changes to the fuel injection equipment, or adjustment of the camshaft to allow for elongation of the timing chain.
An evenly balanced engine is desirable because it ensures that the engine is operating at its maximum efficiency and will prevent overloading of individual cylinders which can lead to excessive bearing loading and crankshaft vibrations and stresses.
Cylinder power output is directly proportional to the Mean Indicated Pressure which is again proportional to the amount of fuel burnt in the cylinder, but before adjusting the fuel pumps, the draw cards (or crank angle diagram) should be examined to ensure that compression pressures and peak pressures are the same, and that there are no faults with the fuel injection. If compression pressure is down on an individual cylinder, it may point to poor ring sealing or leaking valves. If the peak pressure is too low or too high, then fuel timing should be checked.
Also to be taken into account are the exhaust temperatures and fuel pump rack setting.
Adjustments should be small, and noted down. After each adjustment, wait for the engine to settle down before retaking the cards.