M20 C Engine Start problems

[MIm20c]

I would disconnect the starter signal wire and make sure you can hear the SOS every time you turn and push in the key. If it sounds like it’s working look up the procedure given earlier in this thread to make sure the left mag is working properly. 

[Urs_Wildermuth]

1 hour ago, MIm20c said:

I would disconnect the starter signal wire and make sure you can hear the SOS every time you turn and push in the key. If it sounds like it’s working look up the procedure given earlier in this thread to make sure the left mag is working properly. 

Yes, the SOS can be heard every time. The left magneto has been removed for repair in the recent maintenance action and should therefore work ok. But one never knows, we will do that.

[Hank]

2 hours ago, Urs_Wildermuth said:

Yes, the SOS can be heard every time. The left magneto has been removed for repair in the recent maintenance action and should therefore work ok. But one never knows, we will do that.

My left [Slick] magneto went to the Kelly factory in summer 2015. On a trip to NC in March 2017, it failed and was sent to Tulsa for overhaul as the condenser wire inside had been placed over the big plastic gear and worn in two, with additional evidence of internal arcing. That magneto failed on my 3 hour flight home . . .

Good luck with your magneto overhaul. I hope it's better than mine was!

[Urs_Wildermuth]

Last update:

We managed to ferry the plane to maintenance.

Normal starting failed. Then we tried twice the method described by several here, cranking and releasing the switch. It did indeed start on the 2nd try.

Arriving at the maintenance airfield, the mechanic had us try again the normal way and it started....

I'd say the main suspect is now the SOS box. But this still does not explain why it starts once and then not. Of course also the box can be intermittendly defective... 

 

[Hank]

Intermittent electrical troubles are difficult to track down. Best of luck! Releasing the key will often make the engine run because it energizes both magnetos at 20°/25° BTDC, where it runs all the time anyway. This will get around SOS and Left Magneto issues.

[MIm20c]

If you can hear the box every time check the wiring from the SOS to the switch and back to the left mag. If everything test normal and is tight on the back of the switch I’d have someone check the left mag again. 

[bob865]

How loud is the shower of sparks vibrator?  I have been having trouble getting my engine to start and after reading this I believe I have a bad shower of sparks vibrator also.  She will only start when I let go of the key and I do not remember ever hearing the vibrator.  Is it loud enough that it is obvious when it is vibrating?

[Andy95W]

Yes, it is definitely loud enough to be heard.  Remember that old "Operation!" Game from the 1970's?  Imagine if that buzzer was inside a Rubik's Cube mounted on the firewall in front of the radio stack.  That's about what it sounds like.

[DXB]

On 2/6/2018 at 9:00 PM, bob865 said:

How loud is the shower of sparks vibrator?  I have been having trouble getting my engine to start and after reading this I believe I have a bad shower of sparks vibrator also.  She will only start when I let go of the key and I do not remember ever hearing the vibrator.  Is it loud enough that it is obvious when it is vibrating?

Can’t be heard easily over the starter spinning the prop.  Turn key to right without pressing in and you will hear the loud buzz without engaging starter.

[Urs_Wildermuth]

Ok, I have gotten the message today that the problem is solved, will have to wait and see what the end result is.

In the end, it appears that the troubleshooting was not as thorough as we thought it had been. On 2nd glance, a lot of problems were found in previously cleared items.

- The carburettor was sent to be checked and the accelerator pump was found faulty. So the original assessment by maintenance was inadequate.

- A new SOS box has been installed. I would like to have the old one bench tested, can Don do this or who can? I simply want to know if it was faulty or not. If it still works or can be reconditioned, I'd like a spare. New ones are $650 or so, so it may be worth looking at it.

- The left magneto was sent for repair and found faulty.

- A new ignition lock was installed and the old one was confirmed faulty. .

 

We will test it next week, we got the message today that the starting now works perfectly in the shop. We'll have to see if it does work nice as well once the airplane is out of the shop....

The way it looks is that we went about rectifying this much too hesitantly. In the end, it was not one element faulty but ALL of those who could have been.

 

[Mooneymite]

The shower of sparks box is pretty sturdy.  The most common parts needing replacement are the points and the condenser.  Usually a bad condenser causes burned points, so both get replaced.  Neither is very expensive.  I would highly doubt that the whole box is bad.

[Guest]

3 hours ago, Urs_Wildermuth said:

Ok, I have gotten the message today that the problem is solved, will have to wait and see what the end result is.

In the end, it appears that the troubleshooting was not as thorough as we thought it had been. On 2nd glance, a lot of problems were found in previously cleared items.

- The carburettor was sent to be checked and the accelerator pump was found faulty. So the original assessment by maintenance was inadequate.

- A new SOS box has been installed. I would like to have the old one bench tested, can Don do this or who can? I simply want to know if it was faulty or not. If it still works or can be reconditioned, I'd like a spare. New ones are $650 or so, so it may be worth looking at it.

- The left magneto was sent for repair and found faulty.

- A new ignition lock was installed and the old one was confirmed faulty. .

 

We will test it next week, we got the message today that the starting now works perfectly in the shop. We'll have to see if it does work nice as well once the airplane is out of the shop....

The way it looks is that we went about rectifying this much too hesitantly. In the end, it was not one element faulty but ALL of those who could have been.

 

Send me a PM and I’ll send you the Shower of Sparks manual if you’d like.

Clarence

[ShuRugal]

On 2/6/2018 at 9:00 PM, bob865 said:

How loud is the shower of sparks vibrator?  I have been having trouble getting my engine to start and after reading this I believe I have a bad shower of sparks vibrator also.  She will only start when I let go of the key and I do not remember ever hearing the vibrator.  Is it loud enough that it is obvious when it is vibrating?

Mine is loud enough that it startled me the first time I started the plane (startled the IA doing my prebuy too, he hadn't seen a SoS system in a while).

In fact, mine is faintly audible over the starter, with my headset on.  it's got some oomph in it.

[jaylw314]

On 2/9/2018 at 2:22 PM, Urs_Wildermuth said:

Ok, I have gotten the message today that the problem is solved, will have to wait and see what the end result is.

In the end, it appears that the troubleshooting was not as thorough as we thought it had been. On 2nd glance, a lot of problems were found in previously cleared items.

- The carburettor was sent to be checked and the accelerator pump was found faulty. So the original assessment by maintenance was inadequate.

- A new SOS box has been installed. I would like to have the old one bench tested, can Don do this or who can? I simply want to know if it was faulty or not. If it still works or can be reconditioned, I'd like a spare. New ones are $650 or so, so it may be worth looking at it.

- The left magneto was sent for repair and found faulty.

- A new ignition lock was installed and the old one was confirmed faulty. .

 

We will test it next week, we got the message today that the starting now works perfectly in the shop. We'll have to see if it does work nice as well once the airplane is out of the shop....

The way it looks is that we went about rectifying this much too hesitantly. In the end, it was not one element faulty but ALL of those who could have been.

 

I don't know, that sounds an awful lot like shotgun maintenance.  How could the accelerator have anything to do with starting?  How was the ignition lock faulty, and how could that lead to hard starting but ok mag checks?  I think you are right to be suspicious of the SOS box.  How was the left mag "faulty"?

In my mind, just a weak left mag would be an adequate explanation.  With a weak spark at low RPMs, you'd have hard starts, but with idle or higher RPMs, the problem would go away.  I didn't see anything about the mags being bench-tested, just checked on runups, right?  And a weak spark would be consistent with what you described requiring a rich mixture and full throttle to start.

[Andy95W]

It does sound like shotgun maintenance, but all of those items can indeed conspire to make for difficult starting.

-accelerator pump: on the carbureted M20C, the only primer the airplane has IS the accelerator pump in the carburetor, so if it was faulty, then the engine definitely didn't have enough fuel to start.

- ignition switch: a lot of stuff happens when you turn the switch to start and push in to engage the starter.  The right magneto gets grounded, the starter gets engaged, the left magneto is advanced to TDC, and the high-energy SOS current is allowed to flow to the left magneto.  If any of those things don't happen, the engine will either not start or be very difficult to start.  None of those additional functions would be found on a mag check on runup.

-left magneto:  there are two sets of points in the left mag, one for normal operation (25° BTDC) and the other is for starting (TDC).  If the starting points were not set correctly or pitted/burned, the engine would either be difficult or impossible to start.  Again, this would not show up on a normal mag check.

[Urs_Wildermuth]

Well, we finally were able to ferry it back to base from maintenance and for the first time I own this airplane it starts like it is supposed to according to POH. 2-3 pushes of the throttle, then it fired after 2 blades.

I think the very critical thing was the SOS box which "pretended" to work but did not really. The other bits and pieces just helped aggravate the situation.

The pump did work but not as it's supposed to, that is why we had to prime 5-6 times instead of 1-2. There was enough fuel, in fact it sometimes overflowed and dripped down... but now it is much faster and we don't have to worry about weird procedures anymore just follow the POH.

Maintenance originally thought that the SOS box was ok as it could clearly be heard. But I think it was not. However, the whole action showed that other stuff also was amiss, particularly the carburettor.

Well, it was a very expensive exercise but at least the end result is finally what it was supposed to be in the first place.

[Hank]

Glad to know you got it fixed. Cs should be easy to start, hot or cold; doing runups during annual and the post-maintenance check flight, my A&P/IA was impressed by how easily she started each time.

[carusoam]

Urs,

Great update!

Recently somebody else came to the same conclusion around here...  the SOS box sounded right, but wasn’t working...

You might compare notes with... @TWinter

Unfortunately it was being chased at the same time.  No opportunity to learn from each other’s experience.

Possibly helps the next MSer with a SOS challenge...

Best regards,

-a-

[TWinter]

As I read this post it sounded all to familiar. Glad you got it up and going and I truly believe your main issue was the SOS. Hopefully our episodes will help the next MS guy/gal when everything looks right, but just isn't. I do credit Mooney Space with a lot of my trouble shooting help that finally helped me narrow it down. With complex electronics and old airplanes sometimes it's hard to pinpoint problems. Glad your up and going, but I think next time one or the other of us tries solving the problem first.  One of us might save a few bucks..

 

-Tom

[1963M20C]

I am currently having the same problem with my C. LAst summer it would fire right up on one or 2 sweeps of the blades. As soon as it started to cool down it became very difficult to start. Now it has been sitting for about 2 months due to bad weather. My brother went to the airport this week and could not get her started. 

[Ragsf15e]

Surefly.  No sos or mag.

[Hank]

57 minutes ago, 1963M20C said:

I am currently having the same problem with my C. LAst summer it would fire right up on one or 2 sweeps of the blades. As soon as it started to cool down it became very difficult to start. Now it has been sitting for about 2 months due to bad weather. My brother went to the airport this week and could not get her started. 

Where are you? How cold did the weather turn?

Living along the Ohio River, my C was much easier to crank in winter if I preheated the engine or pulled into a heated hangar for 30-45 minutes or more [an hour was always good]. Then follow the Cold Weather Starts procedure in your Owners Manual, with one small change:  after pumping the throttle several times, give the cold fuel extra time to evaporate. That's when I wind and set the yoke clock and put on my headset, then crank the engine. Much better!

Now when I travel during cold weather, I take a long extension cord with me to plug in my oil sump heater. Works great!