M20K starting process worse and worse - why does it start with releasing the ignition key?

[NicoN]

At our last annual we lost your primer assembly accroding to the SB.

Before, our 1980 M20K was starting like a charm - at least cold.

But since then starting became more and more a PITA.

Starting needs a lot of fuel and the starter motor has to turn the prop quite a while.

Now we found out that after a couple of seconds it seems to be fine just to release the ignition key and it starts. Sounds funny?

I was thinking of magneto issue, but both of them were replaced with overhauled ones two years ago.

Any ideas on this effect?

 

BTW: my partner recently came up with a document, which says to prime only  3-4 sec in normal mid temperatures while I learned that priming needs 7-8s, more when colder.

Nevertheless; his method also did not work well.

 

 

[Hank]

Engine starting when the key is released is a symptom of a failing left magneto. I had mine overhauled away from home, it failed again on the 3.2 hour return flight.

Reasoning:  with the key turned and pushed, your right magneto is grounded and the left magneto is firing very close to top dead center (the starting timing). When you release the key, both begin firing at 20° / 25° before TDC, igniting the fuel already present. 

[RH Galyen]

Check P leads are correct. Most switches turn off the right mag, on start, if the left mag  has an impulse. 

[N201MKTurbo]

I’m not sure what kind of magnetos you have. My old M20F had that problem once. It had SOS mags. The problem was the retard point lead inside the mag had warn the insulation off the wire and grounded the retard points. I fixed it by putting the spade lug connector on 180 deg. from how it was so the wire didn’t touch the side of the mag any more. If you have impulse coupling mags, see the post above.

[NicoN]

That does not sound promising.  They are more or less brand-new! Only 90h or so.

How to diagnose?

The magneto check was fine. We have  around 50RPM drop, left may be little more than right, if I remember.

I also saw the typical uniform rise in EGTs while checking the magnetos

Do the GAMI test while in flight?

 

Edited September 8, 2022 by NicoN

[Shadrach]

Pretty sure you have impulse coupled mags. Reads like the impulse coupling is not firing, but the engine the starts when the switch moves to both it ungrounds the mags and starts.

Given that your likely starting the engine with a spark firing at 20° BTDC (Normal mag timing) vs 0° (Impulse coupling) there is a significant risk of kick back and starter damage.

if you have an SOS system it could be the switch or the retard breaker.

[Shadrach]

13 minutes ago, NicoN said:

That does not sound promising.  They are more or less brand-new! Only 90h or so.

How to diagnose?

The magneto check was fine. We have  around 50RPM drop, left may be little more than right, if I remember.

I also saw the typical uniform rise in EGTs while checking the magnetos

Do the GAMI test while in flight?

 

This has nothing to do with how the mags operate in the both position. The starting circuit is the problem. You either have shower of sparks (SOS) or an impulse coupling (more likely). For whatever reason, the left mag starting circuit (SOS or impulse coupling) is not sparking in the start position. This is why the engine starts when you release the key back to both. If you continue to operate the engine this way, there’s a good chance it will kick back which could take out the starter shear pin.

[David Lloyd]

2 hours ago, NicoN said:

 

Before, …was starting like a charm - at least cold.

But since then starting became more and more a PIT.

 the starter motor has to turn the prop quite a while.

Now we found out that after a couple of seconds it seems to be fine just to release the ignition key and it starts. Sounds funny?

I was thinking of magneto issue, but both of them were replaced with overhauled ones two years 

 

 

 

Several years ago, I could have written this.

2 hours ago, RH Galyen said:

Check P leads are correct. Most switches turn off the right mag, on start, if the left mag  has an impulse. 

P leads were reversed.

[A64Pilot]

2 hours ago, Hank said:

Engine starting when the key is released is a symptom of a failing left magneto. I had mine overhauled away from home, it failed again on the 3.2 hour return flight.

Reasoning:  with the key turned and pushed, your right magneto is grounded and the left magneto is firing very close to top dead center (the starting timing). When you release the key, both begin firing at 20° / 25° before TDC, igniting the fuel already present. 

I’m with this guy it IS very likely a symptom of a failing magneto, and not the starting system. The system kills the non bendix equipped mag, and if the bendix equipped one isn’t working well, so when the key is released the grounded mag is now hot and starts the engine.

Very often weak magnetos won’t fire at low RPM even with an impulse, but will work well enough at high RPM for a mag check.

It’s not a bad idea to do an unofficial mag check at idle, every so often that can point out a failing mag. Also every now and again turn the engine off with the key, that tells you of course that you don’t have a hot mag

[KSMooniac]

It is a mag problem.  What kind of mags, and who did the overhaul?

[PT20J]

If I were troubleshooting this, I would disconnect the p lead from the left mag making it hot, and ground the p lead on the right mag disabling it. That would eliminate the wiring and switch. If it doesn’t start, it would implicate the left mag.

However, the original post indicates that this issue arose after some change to the primer system, so it might be good to investigate that.

Skip

[kortopates]

1 hour ago, NicoN said:

That does not sound promising.  They are more or less brand-new! Only 90h or so.

How to diagnose?

The magneto check was fine. We have  around 50RPM drop, left may be little more than right, if I remember.

I also saw the typical uniform rise in EGTs while checking the magnetos

Do the GAMI test while in flight?

 

You're lack of understanding of Mags is preventing you from understanding what folks are trying to tell you here.

You can't tell a thing about the independent starting circuitry of your Mag from a Mag check. What you need to understand is that when you are starting the engine the Mag(s) use a different circuit or method to retard the timing in order to start the engine versus the 20 BTDC once it starts. Two entirely different kinds or stylers of Mags are used: either a Mag with an extra set of points in it, called the retard points, used to fire at only 0 BTDC when key is in "start". As you release key to start, then it goes to the normal points to run at 20 BTDC (which are the points you are testing during a mag check - not the starting points). The retard points are only used in starting. But not all engine mags use retard points. The other technique or style is called impulse couple mags. These don't have a extra set of points to fire retarded, but the impulse coupling does two things: think of it as a spring that delays turning rotating the mag internally till it's almost ready to fire and then the spring releases to spin the mag magnet much faster than the engine is actually turning over the last few degrees to provide a stronger spark. It also acts to retard the timing while the impulse mechanism is working so it fires at 0 BTDC versus the normal 20 BTDC. 

Consequently you need to know exactly what kind of mags you have to trouble shoot this effectively. What your describing is a failure of the starting mechanism of the MAG and in particular a failure in the retard breaker points since it starts soon as you switch from Start to Both. But most of the later K's came with a pair of Slicks, both  impulse couple mags, which start really easy. But some have Bendix. But what your early 231 has is up to you to investigate. It may turn out to be a more general mag failure too, not necessarily the starting circuitry but your description is pointing to the starting circuitry. 

A simple test can tell you if you have impulse coupling, If you pull the prop slowly and you hear a loud click noise, that is the impulse spring releasing and firing. No click would mean you have a mag with breaker points. (Be careful handling the prop in case you have a broken p-lead). Your engine logs will also identify the kind of mags you have.   

[Fly Boomer]

3 hours ago, NicoN said:

I was thinking of magneto issue, but both of them were replaced with overhauled ones two years ago.

Doesn't matter if they were overhauled five minutes ago -- what's important is their condition now.

[PeteMc]

4 hours ago, NicoN said:

Starting needs a lot of fuel

I know a lot of the real engine guys are telling you lots of things to check with the  Mags, etc.  But as a 1980 K owner I need to ask about your priming?  If I understand the problem correctly...  AFTER they changed your primer assembly you have trouble starting.  AND you are using a lot of "fuel" which I'm reading as a lot of priming.  That mega priming is probably your problem.

With the old prime we shot fuel into one cylinder.  With the new prime you are just basically running the High Fuel Pump and you are putting fuel into ALL cylinders.  So I'm wondering if you're over priming and then cranking until the mixture gets lean enough  to start.  For normal start I now go full rich, full throttle and then give about 3-4 seconds prime.  I then take my my time resetting the throttle and double checking around the plane, calling "Clear", checking around the plane, etc. to give the fuel time to atomize (so at least 10-20 sec), then it usually starts right up.  (Double or more in the winter pending the temps.)

 

[Guest]

The fact that the engine starts when you release the key from the start position would suggest left magneto issues.  in most ignition systems the right magneto is grounded by the ignition switch during starting.  When you give up trying to start and release the key, you open the ground circuit on the right magneto, it comes to life and the engine starts, leading you to believe you flooded the engine.

Removing the old priming system should actually make the engine easier to prime and start, after all you’re delivering fuel directly to the intake port of each cylinder now, just like when the engine is running. In the original configuration you squirted fuel into the front of the intake tubes sharing two priming jets for six cylinders.

[carusoam]

Hey Nico!
 

Summary…ish.

1) Starting after release of the key…. Is often a sign the left mag, starting circuit isn’t working… (might be a broken part of the Left mag)

2) The mag switch is complex… decades and thousands of hours may have it not working correctly… an OH is possible…. (Might be a broken or worn part of the ignition switch)

3) once started, the pilot won’t know that the starting circuit isn’t functioning properly…. (This circuit is only used for starting)

4) Often starting circuits include mag timing for the start at TDC…. It’s amazing that it starts using the normal mag timing…. The risk comes in with the prop moving too slowly… the ordinary mag might fire before the piston arrives at TDC…

5) Priming system on the M20K is as complex as it gets… the recent updates alter where the prime gets delivered… these details are worth a review…. The new system behaves much better…

6) Normal start vs Cold start for Continental’s IO550… the Cold start uses 2X the normal start prime… measured in seconds of the fuel pump running….

 

PP thoughts only,

Best regards,

-a-

 

[NicoN]

As I stated, our mags have been overhauled less than 100h ago. So, I am not happy to hear that most likely the mag is faulty (again)

 

 

 

 

[carusoam]

1 minute ago, NicoN said:

As I stated, our mags have been overhauled less than 100h ago. So, I am not happy to hear that most likely the mag is faulty (again)

 

 

 

 

Mag or

wire related to install or 

Ignition switch

It might be a simple fix….

 

But, you are ahead of the game armed with all of the detail you got from the fine MSers in this thread….

Best regards,

-a-

[NicoN]

Thanks to all posters  on this issue.

I think, I learned  that a running engine has nothing to do with a starting engine.

So, our mag check might be useless.

in fact, we did all the mag checks in idle, in flight (according to Savvy).

According to our maintenance maual we have  Slick magnetoes and both are equipped with impuls coupling.

 

@PeteMc: I was  already using the High-Boost-pump-method even before the primer assembly was removed. And it worked fine - far better than the POH-method. But the behaviour changed a lot after teh SB was done. But I will try your method of waiting  quite a bit of time with the shorter priming phase - I never waited 10-20s. Lets see

 

 

 

[Aerodon]

I think you are getting it now.  Both mags have an impulse couple, when in the 'start position' both should still be working.  You should be a little sceptical about freshly overhauled mags, maybe not so much after 100 hours, maybe again after 5 years.  Harness condition?  Be sceptical of Champion spark plugs, do the resistance check under pressure.

Finally, part of the SB to remove the primer diverter valve is to make sure you have the correct 'new style' primer nozzles (see picture).  The new ones are taller and create a little dam of fuel.  Allowing some time to evaporate may help.  And remember you are now priming 6 cylinders at once, you need to find a new 'happy place' for priming duration, waiting, temperature and cranking duration.

 

Aerodon

 

[Guest]

2 hours ago, NicoN said:

Thanks to all posters  on this issue.

I think, I learned  that a running engine has nothing to do with a starting engine.

So, our mag check might be useless.

in fact, we did all the mag checks in idle, in flight (according to Savvy).

According to our maintenance maual we have  Slick magnetoes and both are equipped with impuls coupling.

 

@PeteMc: I was  already using the High-Boost-pump-method even before the primer assembly was removed. And it worked fine - far better than the POH-method. But the behaviour changed a lot after teh SB was done. But I will try your method of waiting  quite a bit of time with the shorter priming phase - I never waited 10-20s. Lets see

 

 

 

Not knowing your serial number, this SI might apply to you for improved starting.  S/I M20-59A

https://www.mooney.com/wp-content/uploads/2020/12/SIM20-59A.pdf

[Fly Boomer]

11 hours ago, NicoN said:

I was  already using the High-Boost-pump-method even before the primer assembly was removed. And it worked fine - far better than the POH-method. But the behaviour changed a lot after teh SB was done. But I will try your method of waiting  quite a bit of time with the shorter priming phase - I never waited 10-20s. Lets see

Mike Busch says, as a general rule, if you are having trouble starting and it's cold out you are probably not priming enough; if it's warm, you are probably over priming.  Of course none of that matters if you have wiring issues or bad mags, regardless of when they were overhauled.

[Ragsf15e]

42 minutes ago, Fly Boomer said:

Mike Busch says, as a general rule, if you are having trouble starting and it's cold out you are probably not priming enough; if it's warm, you are probably over priming.  Of course none of that matters if you have wiring issues or bad mags, regardless of when they were overhauled.

Agreed.  It takes reasonable spark too.  Obviously the starting circuit seems most likely, but what type and how old are the plugs?