Starting problems on M20J continue

[NotarPilot]

After my last post I got some great feedback and thought I fixed the problem. Maybe I did and maybe this is a new problem. Based on some of the advice I received I replaced my 18 year old Skytec starter with a rebuilt one from Skytec. The prop turns over faster and stronger now but starting is still a problem and getting worse. I started thinking it was the contacts in the ignition switch but maybe it's not. Here's what's been happening...

First of all the problem is intermittent. Sometimes I turn and push the key and the prop turns and the engine starts right away. Sometimes the starter will engage and disengage, turning the prop maybe half a revolution. I'll release pressure on the ignition key then push in again to re-engage the starter and it'll turn and start. This might take 2-3 attempts sometimes. 

Today I flew a cross country flight, landed and refueled. Same deal when I first started it today. After refueling I tried to start the engine so I could taxi it to a parking spot and all I got was a click.  I attempted to start it about 5 times and still just a click each time. No turn of the prop, nothing, just a click sound. I get out, turn the prop and try again, still just a click. I get the tow bar out and schlep my plane over to a parking spot. I decided to try one more time before leaving the plane parked. I engage the starter and the prop starts turning right away like normal. 

This is the first time the problem was this bad.

I checked the Skytec troubleshooting chart and it doesn't cover a scenario where the problem is intermittent. Any ideas on what the problem is?

[Shadrach]

I thought it was a ground issue or perhaps an ignition switch issue the first time around. Those are still avenues I would investigate.

[NotarPilot]

You don't think it could be a starter relay?

[ArtVandelay]

2 hours ago, NotarPilot said:

You don't think it could be a starter relay?

If you are hearing the relay click, that tells me the switch is good.

It could be a bad connection, or a bad contact internal to the relay. Spruce has relays for $70 that are approved/certified (Skytech STS-S12), I would replace it and while at losen the starter cable connections, clean them, an retighten.  Any bad connection in the chain could cause what you are seeing, including ground contacts, battery cables.

[Guest]

I'd would suggest something in the starter control circuit, either the switch or relay. You can take a jumper wire from the main buss through a spare circuit breaker then out the side window.  Connect it to the control terminal of the starter relay(disconnect the original wire) Open the circuit breaker, turn on the master switch then use the circuited breaker as a starter switch.  

If it cranks steadily the relay is likely not your trouble and more likely the magneto switch, which can be removed, disassembled and cleaned, or simply replaced.

Clarence

[Yooper Rocketman]

I had a teaching moment with a couple of my younger techs last fall when my D-4 Cat Dozer was doing the same thing.  They were ready to start swapping parts until I came over and insisted they diagnose the problem instead.  With the starter switch engaged by one tech (and the starter NOT engaged), I had the other tech check where he had power (and ground via voltage drop check) going down to the starter.  Everything showed power when and where it should be but the actual starter coming out of the Bendix at the starter stud.  On relays, they usually have static power and ground, and the small "sw" terminal is feed by the starter switch.  This energizes a coil that moves a contact plate inside the relay to close the contacts between the large studs and on to the next component.  Some systems use a small relay on the firewall for this, some are just on the starter.  On the dozer, the Bendix was "clunking", clearly getting power, but when putting a voltmeter across the large studs, power was not transferring from the power stud on the relay to the actual power stud on the starter.  Disassemble found the typical problem, the contact plate arced up badly enough it wouldn't conduct between the studs when the plate was thrust against the stud ends.  

Your relays on our airplanes are likely "pressed" together, where you can't disassemble it short of destroying it to see the actual problem.  But, verifying where your power flow is interrupted will be far quicker and cheaper than throwing components at the problem.  Many starting problems will be of this nature, but I have seen a ton of starting problems go back to loose or corroded connections, and even crimp or solder ends on cables not passing the power through.  Those problems can be diagnosed with a simple voltage drop check (running your volt meter leads from point to point of a circuit to see if the voltage will take your meter path instead of the designed path, because your meter is the path of least resistance).

Not sure if it's practical, but someone with comfort with this type of diagnosis could likely nail the problem down in a few minutes (when it is actually acting up).

Tom

[ArtVandelay]

If checking voltages, you need to do it with the circuit active, if there is no current, there may be no voltage drop unless the there is a complete break in the circuit, a corroded connection would allow the other side to show voltage, but will not pass enough current to drive the starter.  Had this problem with a CB (brand new).

[Yooper Rocketman]

2 hours ago, teejayevans said:

If checking voltages, you need to do it with the circuit active, if there is no current, there may be no voltage drop unless the there is a complete break in the circuit, a corroded connection would allow the other side to show voltage, but will not pass enough current to drive the starter.  Had this problem with a CB (brand new).

Essentially that whole diagnosis process described by me was during an active current situation (starter switch engaged with no crank).  Agree you need draw for "most" voltage drop tests, but if you have a loss of voltage during static testing, before even applying a load, then the VDT will work then too.  But then you could do a simple voltage check to find the same problem then.  The great thing about a VDT is you may find multiple points of resistance in a circuit, sometimes eliminating a future failure point (such as a cable or connection allowing a small amount of voltage through the meter instead of the correct path) as well as fixing the current issue.  I've seen on intermittent electrical issues many times getting 1/2 a volt or more on a static circuit, which would give you a starting point for a problem that won't rear itself during diagnosis.

Tom

[Andy95W]

Starter relay from my experience.

Over the years of very slight arcing inside the starter relay, carbon builds up and the contactor erodes.  Now the electro magnet still makes a good solid clunk but the contactor only intermittently allows enough current to flow that will actually allow the starter to turn the engine over.

[NotarPilot]

I'm thinking it's the starter relay too but would that explain the intermittency of it? 

[Andy95W]

2 hours ago, NotarPilot said:

I'm thinking it's the starter relay too but would that explain the intermittency of it? 

Yes.  I owned an Aztec that had this exact symptom.  Sometimes the contactor made a good clean connection, other times it didn't. Sometimes I had to "blip" the starter switch to get it to work.  New starter relay made it reliably consistent.

I am not guaranteeing that this will fix your problem, but your description matches my experience to a 'T'.

When/if you change your relay, make sure you clean up your cables really well where the ring terminals attach to it.  

This one is a good price and is PMA'ed for the M20J:

https://www.aircraftspruce.com/catalog/eppages/sts-12s24s.php?clickkey=150737

[NotarPilot]

Thanks for the suggestions everyone. I'm going to do some diagnosing and swap out the starter relay.

[Shadrach]

12 hours ago, NotarPilot said:

I'm thinking it's the starter relay too but would that explain the intermittency of it? 

Relays can be intermittent.. I've encountered several vehicles over the years with fuel pump relays that inermitantly fail. The relay flips, but does not always complete the circuit.

[Browncbr1]

You probably already did, but did you check battery voltage?   Maybe your generator/alternator isn't charging or belt is loose??   

[carusoam]

Quirky thing about electromechanical devices... They wear and they get dirty.  In some cases the wear is responsible for the dirt.

With respect to relays...

I would be inclined to find out how old it is...

When it's 20+ years old with 2000+ hours on it, I could probably remove it, shake it up, test if it works, measure resistance, but realistically. Once you go that far, the money spent will probably have been better spent replacing it.

unlike other maintenance challenges where unnecessary swaps can generate more work than they solve, this one is hard to get wrong. If you swap out a good relay for a new relay, you probably won't need to revisit it again during your ownership.

but...

 

1) How many relays are really involved...?

- master power relay

- starter relay

- just because they mechanically close doesn't mean it makes a clean, resistance free, connection.

 

2) How many other electromechanical devices are in line...?

- Ignition switch 

- This was the last failure on my M20C.  It failed in the hands of the new owner...

 

3) What else is in the line that can be cleaned, re-connected, or re-grounded?

- Check POH wiring diagram for the main obstacles.

- know that all the grounding straps may not be depicted there.

- is it possible that the starter mount isn't grounding, loose or dirty..?

 

 

Collective thoughts from MS.  I am only a PP, not a mechanic...Not recommending swapping out things that are known to be working properly.  There are two other relays on board.  One gives me fear of failure, the other rarely gets used...

Best regards,

-a-

 

 

[Yetti]

Relay would be a good start.   Just because the master is passing enough current to engage the starter relay via the ignition switch does not mean that the master relay is passing full current or dropping out when full current is needed.   The most insidious to find would be corrosion in a connector that looks good on the outside and has been shined up in the terminal part.   All terminals should be shiny from the battery forward.

[Andy95W]

3 hours ago, Yetti said:

Relay would be a good start.   Just because the master is passing enough current to engage the starter relay via the ignition switch does not mean that the master relay is passing full current or dropping out when full current is needed.   The most insidious to find would be corrosion in a connector that looks good on the outside and has been shined up in the terminal part.   All terminals should be shiny from the battery forward.

Hmmm...

 I've usually found that a weak master relay will show itself as a charging problem/weak battery, a bad starter relay will show as a weak starter...

[NotarPilot]

3 hours ago, N1395W said:

Hmmm...

 I've usually found that a weak master relay will show itself as a charging problem/weak battery, a bad starter relay will show as a weak starter...

When the starter turns it gives no indication of being weak. I just replaced it in January. The old one was 18 years old. The new (rebuilt) starter turns stronger than the my old one. I'm hoping it's the starter relay because that's an easy fix. How easy/affordable is the master relay?

[carusoam]

Andy posted a link for a relay above, from AS, less than $100.  ( Check all details)

Best regards,

-a-

[N601RX]

4 hours ago, NotarPilot said:

When the starter turns it gives no indication of being weak. I just replaced it in January. The old one was 18 years old. The new (rebuilt) starter turns stronger than the my old one. I'm hoping it's the starter relay because that's an easy fix. How easy/affordable is the master relay?

The master and starter relay are about the same price from Skytec.  Until recently they were not an option.  If its the master you will see it show up on your volt meter in the panel during starting. Another thing I've noticed is that some of the large gauge wire on my plane looked fine on the outside, but if the insulation was peeled back there was a lot of white powder inside.  I've replaced most of it, but its very unlikely the wire would cause an intermittent issue. The connection between the wire and compression lugs on the ends are a possibility.

[Andy95W]

7 hours ago, NotarPilot said:

When the starter turns it gives no indication of being weak. I just replaced it in January. The old one was 18 years old. The new (rebuilt) starter turns stronger than the my old one. I'm hoping it's the starter relay because that's an easy fix. How easy/affordable is the master relay?

Sky-Tek is now also making a PMA'ed continuous duty solenoid (Master relay) also for about $70.  This is incredibly good news, since the OEM relay is well over $300.

https://www.aircraftspruce.com/catalog/eppages/sts-12a24a.php?recfer=4275

Both relays are right next to each other so also pretty easy.  Replacing both would give you the opportunity to clean just about every important electrical connection on your airplane.

Looking forward to hearing what you decide and how it works out.

[ArtVandelay]

Just now, N1395W said:

Both relays are right next to each other so also pretty easy.  Replacing both would give you the opportunity to clean just about every important electrical connection on your airplane.

Looking forward to hearing what you decide and how it works out.

IIRC, the footprint looks different, some customization maybe require to install the new relay.

[Andy95W]

 

1 minute ago, teejayevans said:

IIRC, the footprint looks different, some customization maybe require to install the new relay.

I believe this is correct, though not significant for your A&P, probably an extra hour of shop time.  The starter relay is a direct replacement.

And I think I mis-spoke:  on vintage Mooneys they are next to each other on the firewall, I believe on the J they are in the tail?

Edited March 22, 2016 by N1395W

[ArtVandelay]

Yes, the J has them in the tail.

[N201MKTurbo]

I believe both those relays are in the parts manual. One is a Cuttler-Hammer the other is a Stancor (now Skytec).