since 1940

Lycoming or Continental aircraft engine kicks back on start

1. Severe kickbacks on engines with "Shower of Sparks" ignition systems are due to the retard breaker points not closing  resulting in a start attempt on the advance points. Improper timing of the retard breaker points.

When the starter switch key is turned to the START position, several things must happen at once:  the normal P-Leads of both magnetos are grounded to prevent the magnetos from firing too early, the P-Lead to the retarded points in one of the magnetos is un-grounded to enable firing at TDC, the “shower of sparks” vibrator is turned on and the starter relay is activated.  If any one of the following problems is present, a kickback may occur:

• The key-switch is bad and one of the normal P-Leads remains ungrounded during cranking.  This allows the normal, advanced points to fire early and cause a kickback.

• One of the P-Leads is broken or loose.  This allows the normal, advanced points to fire early and cause a kickback.

• One or both of the magnetos are defective.

For Shower of Sparks wiring diagrams and installation information a good reference is Teledyne Continental Service Information Letter SIL648. (Continental now owns the Bendix magneto).

Copy of SIL648 in Adobe Acrobat format

On Continental engines, severe kickback will break the starter adapter. This can be caused from the a broken wire to the retard breaker or a poor connection at the magneto.

Continental starter adapter and starter adapter shaft with spring installed.

2. Impulse coupling flyweights are not engaging. Replace impulse coupling. Very early Bendix impulse magnetos had only one stop pin and used impulse flyweights without springs. If the magneto were mounted so that the stop pin was at the top then the gravity would hold the flyweight in and it wouldn't engage. The second stop pin was later added so that at least one stop pin was at the bottom of the flyweight travel circle. Later flyweights have a spring to help hold the flyweight out. If you have this old style then it should be replaced with the newer "snap-ring" style that is more reliable. A second stop pin should be added also.

Bendix impulse coupling with broken rivet.

Newer "snap-ring" style Bendix impulse coupling.

3. Changing from Slick 4000 or 4100 series magnetos to the newer 4200 or higher series magnetos may cause kickback since the new magnetos will deliver a spark at a lower starter cranking speed. The non-impulse must be grounded during start. This does not apply when two impulse coupling magnetos are used. Refer to Slick Service Bulletin 1-79A 4. Attempting to start on the "both" magneto position with an impulse magneto installed.

4. Non-impulse coupling magneto not grounded during start.

5. Improper magneto to engine timing.

6. Mismatch between engine cranking speed and impulse coupling lag angle. The faster the cranking speed the less the lag angle should be. Hand propping with a small impulse lag angle (as you might find on some O-235L2C Lycoming's with the 5 degree impulse coupling)

7. You have a separate push-button for the starter and you are cranking with the magneto switch in the BOTH position. This allows the magneto that does not have a coupler to fire early and cause a kickback. You may get away with this starting procedure for years and hundreds of starts as the spark will be weak - but, one day, the mixture, temperature and fate will be just right an you will have a kickback. You have a separate push-button for the starter and you are cranking with the magneto switch in the LEFT position. A defective switch or broken or loose P-Lead to the right magneto, allowing it to fire while cranking and cause a kickback.

To Kill and kill and kill was the cry. To burn, to destroy, to devastate, to lay waste. Men heard the madness and knew it for madness and embraced it, some with fear and some with joy. Kill or be killed. Survive or parish. The Red Knight of Germany by Floyd Gibbons 1927

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