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Instruments
On a new aircraft or engine change or instrument change, it is important to check that your instruments are giving you correct readings. Time after time we have had issues which end up being a tacho or oil pressure reading being incorrect. The VDO tachos can be fine tuned or calibrated to ensure accurate readings. This is best checked using an optical tacho on the prop although some folks have used a fluorescent light to 'freeze' the prop at 1500 RPM. Oil temperature can be checked by removing the transmitter at oil change time, rigging up an earth wire from the body of the transmitter to the engine earth, and dunking it in a thermos full of hot water which has a calibrated thermometer in it to use as a comparator. When replacing it, remember to use a smear of Loctite on the transmitter when reinstalling it. Oil Pressure is a bit more difficult, but ST have a pressure gauge which can be used for this purpose. Note that if you are fitting an EIS or any other non-standard engine monitoring Instrument, you may need to change the Oil Pressure Transmitter to an alternative type which is matched to the requirements of your EIS. Idle Setting This may be the most neglected item of the engine. Firstly idle is preset for a number of reasons. Engine operation in the air, taxi speed, starting speed etc. Cold idle is usually 75-100 RPM lower than when hot. Idle set for both engines when hot is around 700-800 for the 3300 and 850-925 for the 2200. At those settings engine “feels right” and starting works best. Idle set is by the 7mm set screw onto the throttle shaft. Idle air bleed is located next to the vacuum nipple and should be out around 1 turn to 1 ¼ turns. Correct starting procedure involves throttle closed (hence correct idle setting) and choke on, however very soon after pressing starter choke should be eased off. Prolonged cranking with the choke “ON” will only cause flooding. Hot starts require no choke. When using a new engine the idle will most likely need to be reset after a few hours operation. This function cannot be pre set during the “Dyno break in” and has to be done by trial and error due to the proximity of a large and sharp Propeller spinning close to the engine! Ignition Coils The gap between the poles of the coil and the flywheel magnets should be periodicaly checked to 0.010". there are 4 points to check on each engine (ie 2 coils x 2 points)
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