Sometimes engine starts when I RELEASE the key

[Kiddo's Driver]

O-320-D2A, 1700 SMOH, 10 year old Slick magnetos with a couple hundred hours on them.
Most of the time it starts up just fine. Sometimes you crank away, nice & fast, but it doesn't start. When you release the key to give up on that try at starting it starts right up.
I know the non-impluse coupled magneto is grounded during the start. Maybe it is spinning fast enough to produce a good spark when you release the key & it un-grounds?
If that is what is going on, then I have an intermittent fault on my impulse couple magneto, right?

 

[bnt83]

Don't chase starting issues on Lycoming O320, they are terribly inconsistent IMHO.

 

[Magman]

It is possible your P-leads are swapped which would act that way.

Could be at either end.

Timing light or meter will tell.

 

[bradg33]

Bingo. Your left mag is having some sort of starting issue, so it's only starting when it's still rotating (creating a spark) but the right mag is no longer grounded out. So you either have an impulse coupling issue or some other issue with the left mag.

Same thing can happen on shower of sparks mags when the shower isn't working; when you release the key and un-ground the right mag, it sometimes starts. Not really very good for it, as sometimes, rather than actually starting, it can result in a hard kickback and can damage things.

 

[Skip Miller]

@Kiddo's Driver It could also be a starter switch issue.

Is it a Bendix Key switch with Off Both Left Right Start positions?

If yes, this switch has an AD against it, and what you describe is exactly what the AD is about. Hold a good switch in the start position fully rotated against the stop, then one mag is grounded (the non-impulse mag) allowing the engine to start on the impulse mag. In its failure mode, holding the key against the stop while cranking, both mags are grounded. Crankie but no startie! releasing the key to the run position, and the engine will frequently fire and start. Happened to me in an Archer.

-Skip

 

[Kiddo's Driver]

It is an off left right both with push to crank.
I THOUGHT I read that the Bendix-King AD was NA due to not installed. I’ll definitely check it.
Thanks!

 

[Dan Thomas]

If yes, this switch has an AD against it, and what you describe is exactly what the AD is about. Hold a good switch in the start position fully rotated against the stop, then one mag is grounded (the non-impulse mag) allowing the engine to start on the impulse mag. In its failure mode, holding the key against the stop while cranking, both mags are grounded. Crankie but no startie! releasing the key to the run position, and the engine will frequently fire and start. Happened to me in an Archer.

Nope. It's fault in the Off position that's covered by the AD.

1. For switches subject to this AD, conduct the following checks within the next 100 hours' time in service and each 100 hours thereafter to detect possible switch malfunction:

(a) Observing regular ground run-up procedures, allow the engine to reach operating temperatures and perform a normal magneto check.

(b) With the engine at normal idle, rotate the switch key or lever through the "OFF" detent to the extreme limit of its travel in the "OFF" direction.

(c) If the engine stops firing, this indicates an airworthy switch.

(d) If the engine continues to run with the switch in the extreme "OFF" direction indicating a malfunctioning switch, prior to the next flight accomplish Part III outlined in Bendix Service Bulletin No. 583, dated April 1976, for Repair and Replacement or use an alternate method approved by Chief, Engineering and Manufacturing Branch, Eastern Region.

https://drs.faa.gov/browse/excelExt...5D956BD86256E520053A53E.0001?modalOpened=true

You have a different problem with that switch.

 

[Dan Thomas]

It is an off left right both with push to crank.
I THOUGHT I read that the Bendix-King AD was NA due to not installed. I’ll definitely check it.
Thanks!

The Bendix (not Bendix-King, which is applicable to radios) AD specifically mentions a push-to-start version:

76-07-12 BENDIX IGNITION SWITCHES: Amendment 39-2575 as amended by Amendment 39-3024. Applies to all aircraft employing magnetos and using Bendix ignition switches listed in the table below except switches identified by four digit date code (new) adjacent to the model number or a white dot (modified) on the support plate adjacent to the Bendix logo.

Bendix Switches	Rotary Action, Key or Lever Actuated
Switch Function	Bendix (series) Part Numbers
Twist-to-Start	10-357XXX, 10-126XXX
Twist-to-Start/Push-to-Prime	10-357XXX, 10-126XXX
Push-to-Start	10-357XXX, 10-126XXX, 10-157XXX

 

[Magman]

Couple ways to Determine the type of switch

Do not disconnect wire!

Some have an ID plate on the front.

1. Black wiring plate = Bendix

2. White = ACS

Some recent use Green whivh I think is ACS


If you need to drop switch down do it by removing the ring nut.

No wires disconnected.

 

[flyingron]

Nope. It's fault in the Off position that's covered by the AD.

1. For switches subject to this AD, conduct the following checks within the next 100 hours' time in service and each 100 hours thereafter to detect possible switch malfunction:

(a) Observing regular ground run-up procedures, allow the engine to reach operating temperatures and perform a normal magneto check.

(b) With the engine at normal idle, rotate the switch key or lever through the "OFF" detent to the extreme limit of its travel in the "OFF" direction.

(c) If the engine stops firing, this indicates an airworthy switch.

(d) If the engine continues to run with the switch in the extreme "OFF" direction indicating a malfunctioning switch, prior to the next flight accomplish Part III outlined in Bendix Service Bulletin No. 583, dated April 1976, for Repair and Replacement or use an alternate method approved by Chief, Engineering and Manufacturing Branch, Eastern Region.

https://drs.faa.gov/browse/excelExt...5D956BD86256E520053A53E.0001?modalOpened=true

You have a different problem with that switch.

Unfortunately the test is a cop out. I had a bendix switch that would pass that test perfectly, but would still leave one mag ungrounded when you removed the key.

 

[Kiddo's Driver]

The Bendix (not Bendix-King, which is applicable to radios) AD specifically mentions a push-to-start version:

76-07-12 BENDIX IGNITION SWITCHES: Amendment 39-2575 as amended by Amendment 39-3024. Applies to all aircraft employing magnetos and using Bendix ignition switches listed in the table below except switches identified by four digit date code (new) adjacent to the model number or a white dot (modified) on the support plate adjacent to the Bendix logo.

Bendix Switches	Rotary Action, Key or Lever Actuated
Switch Function	Bendix (series) Part Numbers
Twist-to-Start	10-357XXX, 10-126XXX
Twist-to-Start/Push-to-Prime	10-357XXX, 10-126XXX
Push-to-Start	10-357XXX, 10-126XXX, 10-157XXX

I fixed the “King” part.
I would be surprised if my 1992 aircraft had a 1976 AD applicable to it.

 

[FORANE]

Not applicable in the case the op describes in post 1 but an e-mag can do the same thing. In the case of the e-mag, if the battery voltage reaching the e-mag drops below 9 volts (I think it is) the e-mag will not fire. When the power is stopped from the starter the e-mag can get the required voltage and fire just after stopping cranking. This tends to occur in the winter with cold temperatures. The optional separate 9v battery circuit for starting rectifies this issue.

 

[Dan Thomas]

would be surprised if my 1992 aircraft had a 1976 AD applicable to it

Read that AD. Switches made after a certain date before the AD were fixed at the factory. The updated switches are marked.

But you might have an ACS switch to which an entirely different AD applies every 2000 hours no matter when the switch was made. Bit of a design deficiency.

 

[Dan Thomas]

Not applicable in the case the op describes in post 1 but an e-mag can do the same thing. In the case of the e-mag, if the battery voltage reaching the e-mag drops below 9 volts (I think it is) the e-mag will not fire. When the power is stopped from the starter the e-mag can get the required voltage and fire just after stopping cranking. This tends to occur in the winter with cold temperatures. The optional separate 9v battery circuit for starting rectifies this issue.

That was a problem in old cars. Points and capacitor ignition. For 20 years or so they used a coil rated for 8 volts instead of 12, and a big resistor was wired into the line between the ignition switch and coil. When starting, full battery voltage went to the coil from a separate terminal on the switch, to counteract the voltage drop caused by the starter's draw. Sometimes that part of the switch failed and the engine would only catch when the key was released. If the resistor burned out the engine would only fire while cranking.

 

[Gary Ward]

Read that AD. Switches made after a certain date before the AD were fixed at the factory. The updated switches are marked.

But you might have an ACS switch to which an entirely different AD applies every 2000 hours no matter when the switch was made. Bit of a design deficiency.

Here's my ACS switch at approx 2000 hrs since new. It was working just fine, I bought the kit for diode that goes on the starter relay coil. It was 18 bucks a few years ago. One of the cheaper upgrades that have done to the plane.

Directions said to paint the screw heads red indicating that it has been updated?