No Wire from retard point to buzz box - Why does my plane start?

[Skates97]

I've had my plane since December and have put over 100 hours on it. It has an O-360-A1D in it and the mags are Model 4370 (rev E) and 4347, with the shower of sparks. The only problems I ever had with starting was when it was hot and after I replaced the starter solenoid those went away. Other than that it has always started easily.

I had the 500 hours inspection done on my Slick Mags. From what I knew they were at 530 hours. It's possible they were older than that because the log entry only says "swapped mags" as part of an engine tear-down after a prop strike about 10 years ago, but doesn't say how many hours were on them at that time. The mag checks were always good, but I went ahead and had them done anyway. The mag checks are now about what they were before, but it seems that it has more power. I've taken off from Corona 40+ times and know right where I typically leave the ground. Last night I was off the ground about 200+ feet sooner than normal for when I am flying alone. That doesn't make much sense to me because I was making 2,700 rpm before having the mags done and still making 2,700 rpm so I'm not sure what is making the difference, perhaps someone can explain it.

Anyway... The A&P left me a message Monday that the plane was done and back in the hangar but to give him a call because there was something "odd" that they had found. (Not exactly what you want to hear). I called and he asked how long I had had the plane for and if I ever had trouble starting it. I told him since December and no with the exception of the starter solenoid. He said that when his mechanic was putting the mags back on that he didn't see a wire from the buzz box that would go to the retard points. He told him he must have just missed it, but they both looked and couldn't find one. He told him to go ahead and put everything back together but that he was sure it wouldn't start.

They got it all together and tried starting it. Two blades and it fired right up to their surprise. They tried it four more times and every time it fired up after two blades. He told me he's still not sure why it starts without that wire running from the retard points to the buzz box, but that it starts so well he didn't want to add anything to it that wasn't already there.

[Yetti]

I thought on some models the Key switch grounds out one of the mags and fires off the SoS.   There is a really good thread where someone explains the various methods used on Mooneys

[Andy95W]

My guess- and it's just a guess- is that you have a fairly new battery and a newer light weight starter that spins the engine fairly fast.  That means that it's actually spinning the left magneto fast enough that it is producing enough of a spark to start. 

 

[MIm20c]

I was having some trouble with my new aircraft starting when warm. Because of this my IA and I sorted out the system. 

The SOS gets its power from the same lead as the starter solenoid direct from the ignition switch. The BO output from the SOS goes back to the starter switch and is looped to the LR output which is connected to the left mag.  There is no direct wire, at least on mine, that stretches between the SOS and the mag.  I think this is just another safety so the left retard cannot be energized during flight. 

[Gary0747]

This is intersting. I have not actually heard my shower of sparks buzz for some time but have not worried about it since my airplane starts fine both hot and cold. I do have the wire on the retard breaker connection and have had a light weight starter for some time now.   I wonder if shower of sparks is really needed with the higher speed starters?  

[jamesm]

By any chance  Are your  slick Mags impulsed coupled?    (a very noticeable clicking  or snapping sound as you  turn the prop) 

If I understood you correctly you mentioned that you have Slick Magnetos...  It my understanding the SOS (stating vibrator /shower of sparks) is for the  Bendix  Series 20 and 200 Magneto's not sure about other Bendix models installed in Mooney's .  I am not sure How Slick does their retarding of  the spark on start up  for their Magneto's. Many years ago  Slick had a product called "Slick Start"  I believe it was a  solid state  device and Slick's  answer to Bendix's SOS am not sure if it still out there or not.  I have forgotten which  aircraft catalog that  I saw the   advertising for the slick start. This  was many years ago and there was a particular  model number of  slick start  that was not compatible with Bendix 20/200 Magneto's. Slick  did advertised Model of Slick start for Bendix  20/200 Series Magnetos but when I called to inquire about them  they weren't available. 

It would be pretty impressive that if it starts  in always within 2 blades  without shower of sparks (of some sort  stating vibrator /shower of spark equivalent)  and no impulse coupling and  Mag timing (mag's physical  mounting to the  engine) to engine was in spec.   I would be afraid  to touch it.

James '67C

 

 

 

Edited August 18, 2017 by jamesm

[Skates97]

A&P said it is SOS and if I turn to the start position without pushing the key in I can hear the buzzing. He didn't want to try to change anything because I hadn't had problems and when they tried it would start up right away every time. 

[Raptor05121]

That sounds weird. Now I'm curious how mine work, I don't have a "push to start", I just turn to start and the starter engages. I've never heard a buzzing either. I know I don't have impulse coupling. 

[N201MKTurbo]

The ignition key has to un-ground the main points and connect the main points and retard points together. The output from the SoS is connected to the paralleled points. As the engine rotates the main points opens first but because the retard points are connected the primary coil is still grounded. When the engine rotates to TDC the retard points open. Now both are open and the MAG fires. The SoS supplies additional energy to the primary circuit through the paralleled p-leads to make up for the slow turning magnets in the magneto. 

[orionflt]

No Wire from retard point to buzz box - Why does my plane start?

Because you can't keep a good Mooney down!