M20J won't start and my mechanic is stumped

[PT20J]

1 hour ago, MisfitSELF said:

I’ve kept on digging and what I’ve managed to find is that my A3B6 may be properly configured with the jumper removed.  The Champion/Slick site isn’t really clear but my right Mag (different model number than my left mag) may not have the impulse coupler.

Lycoming shipped my A3B6 with Slick mags: 4372 (impulse coupling) on the left and 4370 (no impulse coupling) on the right. That is the condition that SHOULD have the strap installed as the purpose of the strap is to ground out the right mag so it doesn't operate during starting. Since the right mag doesn't have the impulse coupling, the spark will not be retarded during start and it will fire the plugs too early at the low cranking rpm without the strap. You only remove the strap if you have two impulse mags installed or if you have the dual mag on the A3B6D. Check with your A&P.

Skip

[RogueOne]

On 9/4/2016 at 1:04 PM, pfactor said:

I think I'm going to have to decide between spending around the same amount of money for either a SlickStart or new Tempest fine wires. I'm leaning towards the new spark plugs since I haven't seen any support for the SlickStart idea.

Oh, and the shop that overhauled the magnetos last year says they'll re-inspect and fix them for free. So we're going to do that as well.

The Champions are no bueno.  There is an “in between” regarding Champion massive and Tempest Fine Wire.  Tempest Massives.  I installed and they are a vast improvement.  Do you have a lightweight starter and extra cranking battery?  These made a nice difference in getting the prop spinning for start.  Good luck “finding the culprit in starting dilemma.  My bet is on the Slick mags/mag. 

[201Steve]

Resurrecting this thread. 77j w/ a1b6D I am having trouble starting as of today it was nearly impossible to start and I’ve never had this problem. The D3000 “new” from Kelly is about 400 hours. After some research; it appears I can isolate the p leads simply by removing the p leads and installing the  timing posts. Sounds like this should make both mags all time hot. If it starts, focus on the switch and remedy. If it continues to hard start (or not at all); focus on magneto\impulse coupling. (Side not here; make sure the grounding strap is not installed as it was called out in Mooney si m20-59a applicable to my serial number to ensure impulse coupling is energizing both magnetos). 
 

Today; I cold started OK ish. Seemed to fire a little funny but whatever. Trying to hot start; it was nearly impossible; and propellor back spinning was observed on a slight false start. Very similar results ans the original posters complaints.  After much agonizing I finally got a cylinder firing with a lot of follow thru keeping the starter engaged much longer and barely got it going where it then ran fine eventually. It sounds like it started at 25 advanced and not from the impulse coupling based on commentary regarding back spinning. 
 

ok so eliminate the switch with timing posts; proceed from there. I feel like impulse coupling is the culprit. I looked to see if you could buy an impulse coupling assembly; with no results. Is it true that you can only buy parts for the impulse coupling and rebuild? That’s what it sort of sounds like. Is impulse coupling a part of a standard R&R or overhaul? I’ll probably just send it out as it is near 500 hours anyway. 
 

thanks for any feedback!

[EricJ]

21 minutes ago, 201Steve said:

Resurrecting this thread. 77j w/ a1b6D I am having trouble starting as of today it was nearly impossible to start and I’ve never had this problem. The D3000 “new” from Kelly is about 400 hours. After some research; it appears I can isolate the p leads simply by removing the p leads and installing the  timing posts. Sounds like this should make both mags all time hot. If it starts, focus on the switch and remedy. If it continues to hard start (or not at all); focus on magneto\impulse coupling. (Side not here; make sure the grounding strap is not installed as it was called out in Mooney si m20-59a applicable to my serial number to ensure impulse coupling is energizing both magnetos). 
 

Today; I cold started OK ish. Seemed to fire a little funny but whatever. Trying to hot start; it was nearly impossible; and propellor back spinning was observed on a slight false start. Very similar results ans the original posters complaints.  After much agonizing I finally got a cylinder firing with a lot of follow thru keeping the starter engaged much longer and barely got it going where it then ran fine eventually. It sounds like it started at 25 advanced and not from the impulse coupling based on commentary regarding back spinning. 
 

ok so eliminate the switch with timing posts; proceed from there. I feel like impulse coupling is the culprit. I looked to see if you could buy an impulse coupling assembly; with no results. Is it true that you can only buy parts for the impulse coupling and rebuild? That’s what it sort of sounds like. Is impulse coupling a part of a standard R&R or overhaul? I’ll probably just send it out as it is near 500 hours anyway. 
 

thanks for any feedback!

It does sound like it could be the impulse coupling, especially if you got some backwards energy during start attempts.   And, yes, the impulse coupling should be part of a normal 500-hour/IRAN or overhaul.   It is considered part of the magneto.

[N201MKTurbo]

The impulse coupling is a simple mechanism. I would just pull the mag and look at it.

One thing you can check without pulling the mag, is just pull the prop through and see if it still snaps. If it doesn’t you could have a broken spring or the post fell out.

[201Steve]

Well, went back today and it started pretty well from cold. I didn't have a lot of time, but let it warm for about 5 minutes and tried 2 subseqent "warm" starts and it fired up. Will be curious to see if perhaps it is a true hot start issue after the next flight to full operating temps.

Interesting commentary above regarding baking a magneto in an oven for a true stress test.

 

Could be a sign of an internally degrading magneto that's just showing early signs. We shall see.

[201Steve]

Question for the mag gurus in here.... there isn't any good reading about how the mag retardation works on the impulse coupler. I get that it has a spring and spins the magneto shaft at a higher speed, but I'm not understanding how that also creates a retarded timing. Seems like, all other things equal, a faster spinning shaft would simply ignite the spark at the same time as it normally would. Would like to understand this better......

[MikeOH]

19 minutes ago, 201Steve said:

Question for the mag gurus in here.... there isn't any good reading about how the mag retardation works on the impulse coupler. I get that it has a spring and spins the magneto shaft at a higher speed, but I'm not understanding how that also creates a retarded timing. Seems like, all other things equal, a faster spinning shaft would simply ignite the spark at the same time as it normally would. Would like to understand this better......

I believe there is a separate set of points (retard points) that are set to fire later (TDC?) which are active when the key is in the 'start' position, and disconnected when in R, L, or BOTH positions.