Starter kickback Cherokee 6 260

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Danny Dub

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Danny Dub
On occasion when starting it is like the starter disengages at just the wrong time and the engine spins backwards for several rotations. Usually starts on the next crank. I've never seen an engine kickback so hard to literally spin backwards. Normal deal for a lyc 0540? Plane is new to us...

Thanks,

Dan

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Danny Dub said:
Normal deal for a lyc 0540
Click to expand...
No. Or any other engine. Was it like this since you bought it? Have your mechanic check the magneto timing before you start it again and ensure the mags are operating properly. If it is kicking back hard as you state you can break things internally. I think Lycoming has some guidance on this but I do know TCM has a bulletin out that does address this with a good breakdown on what to look for. A weak starter circuit can also be a contributor but for the most part it's usually a mag problem.
 
Seems to just be on a hot start. Runs great otherwise. Maybe the timing is early and it kicks back too hard. We will investigate further.

Thanks

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What model year Cherokee? Are you following piper’s starting suggestions?
 
Just adding to the warnings.
Depending on your vacuum pump, running it backwards could damage it.
Please update on the resolution/cause.
 
A defective or improperly wired mag switch can do it. If the engine has only one impulse mag, it should be starting only on that mag.

A wrong mag model can do it, too. There are various degrees of impulse retard, and if the mag has too little it will fire too soon before TDC and kickback is the result. And, as Bell206 says, mags set too far advanced will do it, and they'll also damage the engine.

If the vacuum pump fails during kickback, thank your luck. It saved you from an inflight failure. No vacuum pump will fail being spun backward unless its vane wear was really bad. That's one reason why I only bought Rapco or Tempest pumps: they had a means of periodically measuring vane wear so that one could replace it before it failed. Never had an inflight pump failure on any of the school's airplanes that way.
 
Ugh. Can’t be good. Imagine the stress on those parts reversing course. Keep us posted as to root cause.
 
My vote for it kicking back is a mechanical issue if not a procedural issues.

Quite a number for pipers require starting on the left (as I recall) mag since only the left has impulse coupling.
Starting on both can cause a kick back.

If one of these planes and using the proper procedure then.
The switch is wired backwards (including impulse coupling could be on the wrong mag)
Or the impulse coupling in just not working.

If a plane with ignition switch/key start
Switch might be wired backwards
Impulse coupling might not be working.

I am sure there are other things that might cause it as well, timing to far advanced has been mentioned.

Brian
 
The Impulse Coupling is several pieces of steel on the end of a magnet.

If the flyweights in this assembly become magnetized they may not engage

to retard the spark. Then you would get a weak , advanced spark.
 
My vote is starting on both mags. Had this conversation with my instructor since he flies mainly Cessna's. Left mag only.
 
I have to check the POH for The lance I recently starting flying… the checklist does not mention startup on one mag but the checklist is just what’s in the plane might not be accurate…
 
benyflyguy said:
I have to check the POH for The lance I recently starting flying… the checklist does not mention startup on one mag but the checklist is just what’s in the plane might not be accurate…
Click to expand...

The lance also likely has a twist to crank key switch, which the OP’s airplane does not, unless it was added at a later date. The twist to crank key switches will ground a magneto in the start position if it is only supposed to start on one. In other words, the flight manual may remain silent on this because it automatically happens.

Many Lycomings only come with a single magneto that has a start retard of some sort on it, hence my original inquiry in the thread. I still wonder if the OP is or is not starting on left magneto only, since the question was never answered. It may or may not be the problem here (many start fine on both even if it is not correct) but we need to start with the basics.
 
We are having it checked by an a&p. The checklist for the plane doesn't mention one mag start but when starting on left only it has not happened. I'm fairness it has only happened about 2 times or of probably 20 starts so it isn't consistent. I will update when we find the solution

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Ignition Switches with a Start feature have a small jumper that allows 1 mag

inoperative in START. If not installed the non- impulse mag may cause kickback.

If it is installed with 2 impulse mags you are starting on one.
 
Magman said:
Ignition Switches with a Start feature have a small jumper that allows 1 mag

inoperative in START. If not installed the non- impulse mag may cause kickback.

If it is installed with 2 impulse mags you are starting on one.
Click to expand...


Every once in a while I learn something on POA. Did not know this is how they worked. Thanks

Brian
 
Brian Thank you for the Thanks.

My take is forums are intended to allow folks to ask questions or provide

answers as they see fit.
 
I am a new owner of a 1967 Cherokee 6 with a push button start. I’ve been starting it with both mags and didn’t seem to be having any issues but this has got me thinking. I hadn’t heard of impulse coupling before, so I have been watching this thread and doing some reading. According to an article I read you can tell if the mag has impulse coupling by looking for a roughly 1.5” “shim” between the mag and the engine. I checked mine out today and it looks like they both have something between the mag and the engine. Am I looking at the wrong thing or do they both have it?

B19D92D1-6503-47FD-B89B-76978D2D972C.jpeg Left mag

9903493C-E33D-4507-9690-F92C6FC9D2A2.jpeg Right mag
 
It would certainly look like both your mags have impulse couplings. You should be able to hear both of them clank almost together (exactly???) when slowly turning the engine over by hand. Do it switch OFF of course.
 
nrpetersen said:
It would certainly look like both your mags have impulse couplings. You should be able to hear both of them clank almost together (exactly???) when slowly turning the engine over by hand. Do it switch OFF of course.
Click to expand...
I would never trust the switch. Take all the plug leads off before fooling with the prop, listening for the clicks.

Before shutdown we always set the engine at idle and shut the switch off to see if the engine would die, then back on and pull the mixture to kill it. We wanted to know that the switch was doing its job. A lot of pilots never do that and if they have a bad switch or P-lead they might never know it, maybe until the next flight when they can't get a mag drop in the runup. If then, even.
 
Should have mentioned it but I was assuming a previous shutdown with the mixture, and not a Bendix Stromberg carb engine. My friend has a C-85 Aeronca Chief and has to shut the engine off with the switch.:eek:
 
Just to let everyone know the end of the story...

We ended up having the mags sent out for the 500hr check. The impulse coupling was not working properly and I guess there was some other damage internally.

It turned out that the kickback had damaged the starter too so that had to be replaced.

Bottom line, about 3 AMUs later, we are back in business. Thanks for all the comments and suggestions.

Dan

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Bendix ( now TCM ?) Published a booklet “ I am your Impulse Coupling”.

The unit must have a Rodney Dangerfield complex as it is often

misunderstood or ignored with dire consequences including complete

engine failure.

Available on-line, I think.
 
Considering that both the Bendix and Slick magnetos for the 540s have impulse coupler ADs, it would be a good idea to treat them with some respect.
 
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