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Kick back

calbrigsr

calbrigsr

Well-known member
What would cause a engine ( 0540 Fuel injected straight valve) to kick back when trying to start? ( Both mags are impulse mags. ) All ready broke two starters. I was thinking a timing problem, but the boat started when hand propped. ( 5 blade Warp Drive, doing like doing that ).
 
One or could be both, but I doubt it, of your Impulse coupling's are not working, could be a spring or stop pin, when you pull the prop through by hand can you hear the coupling clicking?
 
I just learned something that may or may not apply in your situation: I was turning the engine over with the mags "on" instead of winding up the starter, then turning the mag(s) on while it's spinning.
Because of this and/or the timing being off, the kick-back was so hard the starter bracket became slightly bent and the ring gear got chewed all to hell.

Also, aren't O-540's notoriously hard to turn-over?
 
I never had a problem with my 540 being hard to turn over. Have someone look at it that knows about mags. Like Mike Thurman. There is a few things that could cause it. MOST LIKELY timing, JMO
 
I never had a problem with my 0540. I didn't even have to spin it with the mags off. However it was hard to turn over when it was hot, but never a problem with cold starts.
 
I have not seen this problem, But I was told of someone else having the problem. I was told the teeth for the impulse coupling are worn. I was told they can be turned around to fix it. Eventually they will need to be replaced though.
 
I bought a used rig a few months ago, my problem was a 45 degree impulse,( :shock: ), (instead of 25 degree), it would impulse at 20 degrees past TDC when set at 25 degrees, (ineffective), so when starter spun it fast enough it would crank like a straight mag and kick back sometimes. I've had an impulse hang up due to condensation in accessory case. Found wrong impulse with timing light, in fact, I've allways used auto timing light for final setting of mags, you can find mag problems sometimes at higher rpms.
A trip to Lacy Everette solved problem. :wink:
calbrigsr, if your timing is correct, you have a non working impulse. Turn it thoough by hand and listen for clicks with mags off!! The impulse could be intermittant due to crud buildup. They need to be pulled and checked by a mag man.
 
You have a timing problem. Either your internal timing is off on the mags or your engine timing is off. I'm guessing that you need to pull the mags off and send them to someone who knows what they are doing. Why is it so hard to spend a few buck to solve such a simple problem. Just do it.
 
Like RL Williams said listen for the "CLICK" on the mags when turning the motor over. Or pull the little plugs out of the side of the mag and look through the hole at the plastic gear while somebody turns the prop WITH THE MAG SWITCHES OFF and see if the gear stops while the prop is turning. When the gear stops the impulse coupling is loading and will soon snap and make that loud click. If you do not hear that click then the spring is bad or the catch pins are flat spotted or the coupling arms are rounded. You should hear a click from each mag if they are both impulse and working. I am a believer in hitting the starter button and then throwing the impulse mag switch, instead of throwing the switch and then pushing the starter........Mike
 
When I had a true 170 with helo cam, I set mags at 28 to 30 degrees and had starter humming before I turned impulse mag on, seldom kicked back, but when it did, new starter nose. This engine would turn a 66X36 3350 on the trailer. I had mag marked and if starter broke, I would reset mag to 25 degrees to hand crank.
Now, the reason for my post, has anyone put a GM HEI distributor on an aircraft engine? I guess it would have to drive from camshaft for right rpm. With the timing control you would have, it would make a lot of difference at low and high rpms. I guess it would be too expensive to do.
The timing on A/C engines is only correct at aircraft cruise RPMs, most of our A/B running is a lot less than that.
The electronic ignitions are getting cheaper, (what timing control do they have ?) maybe in a couple of years, this po boy can get one. :wink:
 
You need to make sure that impulse coupling are @ least a 35 if not a 45 degree lag for the fuel injected lyc with angle valves. & that both couplings are working. The must fire after top dead cent. If the fire before top dead center when starting the motor is going to run back wards -kick back. The fuel injected angle valve engine is more sensitive to this than the parallel valve engine. It has higher compression ratio. With working implus couplings you do not have to start the motor first then turn the mags on if your set up right & thing working. Stat with impluse coupting mags on- hot( if the other mag is a non impluse coupling it MUST be grounded out or it will kick back).

The impulse coupling is for 2 reason, To retard the timing so the engine will not kick back during starting. Second it spins the mag over very -fast like then engine was running - so you get a hot spark. The faster you turn a mag the hotter the spark. At engine cranking speed the mag can not put out but a very weak spark if any. The impluse coupling, when it trips, will give a spart hot enough to jump the gap like 1/2". This is why when you turn the engine over by had very slowly you just make the mag click the engine can start. I have sean this one time when some body just leaned on the prop & it moved just faction of an inch & the motor was runing . It had not been started for 2 weeks. This scared the shit out of the people workiing the airplane. None one was in the plane & thy had to catch it.
 
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