since 1940

Hard starting in cold weather

Cold weather causes the obvious reasons for hard starting:

1.including poor fuel atomization
2.low battery voltage and associated starter cranking speed.
3.Congealed oil in the impulse couplings can prevent the impulse couplings from retarding the spark.
4.Ice bridging across the spark plug gaps after a failed start attempt may require removal of spark plugs.

Less obvious is the effect that a weak magneto rotor magnet may have on starting in cold weather. During start the impulse coupling snaps the magneto to a high speed and produces a spark even with a weak magneto. In cold weather the starter turns the Continental or Lycoming engine slower and the engine accelerates slower because of the cold, thick oil. The engine fires, but fails to start because after the impulse snaps, the magneto must produce a spark at near cranking speed to accelerate the engine. If the magneto can't produce a spark at this low cranking speed the engine fires but quits. A normal magneto should have enough rotor magnetism to spark the plug at 150 rpm so that the engine not only fires but continues to run. If the aircraft magneto's rotor magnets are weak, the engine has to turn faster before enough energy is produced to spark the plug. Magneto rotor magnets may be 20 or more years old and have lost much of their strength. magnets are typically not restored to full strength at overhaul because of the high cost of magnetizing equipment. If the magneto is overhauled without re-saturating the magnet then nothing has been done to restore magneto energy. Higher magnet field energy allows the magneto to spark the plugs at a lower cranking speed. This improves cold weather starts.

Comply with Continental Information Letter SIL 00-11B 5/26/04 by replacing drain connector 632068 with  655742 drain connector. For further details see the latest edition of this Service Letter.

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Disclaimer: sacskyranch.com contains abundant information relating to aircraft maintenance. The information provided  is not intended to supercede or supplement the F.A.A. approved  maintenance and/or operator’s manuals. Those F.A.A. approved manuals must be utilized when performing maintenance and/or operating aircraft.