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Why?

cgoldy

cgoldy

Registered User
Moogerah Queensland Australia
Why (often) does the engine start when I release the key?
And why does it often take 6 blades to start with the key and only one when hand propping?
I think I have noticed this with cars as well.

Or am I imagining this?

One mag and one Emag


Col Goldy
 
Take a look at your mag and ignition switch set-up. In the crank position most ignition switches are set up to utilize only the mag with the impulse coupling installed which retards the timing and increases spark output. Usually this is the left mag. Then when you release the switch both mags fire. You say that you have one mag and one Emag. Where is each mounted? Left or Right? The Emag will produce great spark at low RPM since it is powered by the battery and is programmed to automatically retard timing at low rpm. I suspect that you are running the standard mag on the left and that it may be weak, improperly timed, or that the impulse coupling may be malfunctioning. Personally I would set it up to start on the Emag and eliminate the impulse coupling altogether.
 
You probably have a points-related issue on the impulse mag. The other mag is shunted out while cranking but wakes up when you release the key. If pulling the P-lead off the right mag makes the issue go away, you have your culprit, left mag is dying. CAUTION-- the engine will always be hot with a mag lead disconnected.
 
cubdriver2 said:
Mags fire better at a slower speed

Glenn
Click to expand...

To quote from The Magneto Ignition System by John Schwaner “the amount of primary current is determined by how strong and how fast the rotating magnetic field crosses the primary windings”. Page10.
 
hotrod180 said:
Starter might be spinning the engine too fast for the impulse to work correctly?
Click to expand...

You might be onto something here Hotrod. Since I fitted the light weight prop and earthx batery it cranks faster but does not start as easily.

Mag on left and Pmag on right and wired correctly. When hand propping I start it on the impulse only.
 
yup, check your impulse coupling health.. you will break the starter off if impulse fails to engage and retard spark/attempt to kick back....
 
cruiser said:
To quote from The Magneto Ignition System by John Schwaner “the amount of primary current is determined by how strong and how fast the rotating magnetic field crosses the primary windings”. Page10.
Click to expand...

The FASTER the field crosses the coils, the more voltage is produced. Mags get hotter with speed until you reach the point that saturation time becomes an issue. That's why the drag racers use them. As speed increases and saturation time diminishes, induction voltage continues to climb so spark intensity stays relatively constant. With our low RPM engines the spark intensity is hotter all the way to redline. We don't get anywhere near plateau speed.
 
mike mcs repair said:
yup, check your impulse coupling health.. you will break the starter off if impulse fails to engage and retard spark/attempt to kick back....
Click to expand...


All I I know is that it clicks when turning by hand. How else do you check it Mike?

And that doesn't explain why it fires on first blade when hand propping.
 
I wonder if my tach reads when starting. I'll check to see what rpm the starter runs it at. Any one know what RPM impuls couplings work up to?
 
PerryB said:
You probably have a points-related issue on the impulse mag. The other mag is shunted out while cranking but wakes up when you release the key. If pulling the P-lead off the right mag makes the issue go away, you have your culprit, left mag is dying. CAUTION-- the engine will always be hot with a mag lead disconnected.
Click to expand...


I might just swap the wires on the back of the switch and test if it starts better on the emag.
 
cgoldy said:
You might be onto something here Hotrod. Since I fitted the light weight prop and earthx batery it cranks faster but does not start as easily.

Mag on left and Pmag on right and wired correctly. When hand propping I start it on the impulse only.
Click to expand...
If the engine is turning enough faster the impulse will not engage because it thinks that the engine is already running. The impulse fly weights will be centrifugally disengaged. So the spark will be advanced to the run setting rather than being retarded for starting. That is why it starts when hand propping as it's not turning too fast.

If you have both a P-mag and an impulse coupled magneto you should remove the grounding connection on the back of the mag/starter switch. Then when you select start, both will be firing.
 
I have propped a bunch of engines going back to 1911. 20 hp thru a 400 V12 Liberty. Mag speed is important to generate current. The 50 hp Franklin in the Honroit had to be propped closes to the hub to get enough speed. But others like a B5R Kinner on a Fleet will " never " start moveing the prop fast, starts better hardly moving it. We had an Oliver tractor with a mag that we converted to 12V and it spun so fast it wouldn't start till when you released the starter button and it slowed down. The 400 Liberty just like the 680 in the Stearman fired with one hand slowly pullinging the blade. But what do I know?


Glenn
 
Last edited:
“I have propped a bunch of engines going back to 1911.”

Man Glenn, you look great for your age! (If I didn’t say it, you know darn well someone would...)
 
cgoldy said:
I wonder if my tach reads when starting. I'll check to see what rpm the starter runs it at. Any one know what RPM impuls couplings work up to?
Click to expand...
To my knowledge, they typically disengage at about 300-350 engine RPM. I don't think any starter is going to get past about 200 BUT... If you have weak springs (or one broken) in the IC, that number is going to come down. I'd been thinking about it some more and I think you have 1) an internal timing/e-gap issue in the left mag and - 2) a failing IC. Basically time to overhaul lefty.
 
Hardtailjohn said:
I was just gonna say....watch someone that doesn't know how, try to start a Kinner!!
John
Click to expand...

Most time I'm too stupid to understand the why's and what's that make it work. But I'm lazy enough to figure out what it likes to make it work, my bad

Glenn
 
mam90 said:
“I have propped a bunch of engines going back to 1911.”

Man Glenn, you look great for your age! (If I didn’t say it, you know darn well someone would...)
Click to expand...

Dang, I was just going to say something similar. ;-)
 
When someone asks a question about some special technique to get this or that started and the secret start system begins with driving around the hangar in a clockwise direction but under a full moon you must go in a counter clockwise direction or some such BS I always believe that the real answer is basic preventative maintenance. Fuel, air and ignition is all it takes. In the correct proportion. Some folks are too smart for that.
 
skywagon8a said:
.....If you have both a P-mag and an impulse coupled magneto you should remove the grounding connection on the back of the mag/starter switch. Then when you select start, both will be firing.
Click to expand...

FWIW I much prefer a off/left/right/both key switch with a separate starter button.
 
I had this problem after an overhaul and it turned out that the "new" left mag was bad, so it started when you let go of the key to hit both. Make sure it's working. After that the mag check was weird and we weren't getting any drop on right, so we knew something was up.
 
hotrod180 said:
FWIW I much prefer a off/left/right/both key switch with a separate starter button.
Click to expand...

If you have a separate starter button, and 2 impulse mags, is there anything wrong with cranking the starter first to get up to speed and then switching the mag switch to both to start the engine? I know the usual method is to switch on and then crank to start.
 
PerryB said:
To my knowledge, they typically disengage at about 300-350 engine RPM. I don't think any starter is going to get past about 200 BUT... If you have weak springs (or one broken) in the IC, that number is going to come down. I'd been thinking about it some more and I think you have 1) an internal timing/e-gap issue in the left mag and - 2) a failing IC. Basically time to overhaul lefty.
Click to expand...


I think I am seeing 300 rpm with the starter only. But I have a crappy little tach so hard to be sure that low down. But you might be onto it Perry.

So just to recap. Last month before I replaced my heavy borer with the whirlwind and lead acid with an earthex and moved the battery location from rear seat to fire wall, she would start on the second or third blade religiously.
 
Last edited:
AK81 said:
If you have a separate starter button, and 2 impulse mags, is there anything wrong with cranking the starter first to get up to speed and then switching the mag switch to both to start the engine? I know the usual method is to switch on and then crank to start.
Click to expand...
. That is standard operation in radial engines to get some of the oil cleared out of the lower cylinders to avoid liquid lock. I frequently do it on four-cylinder opposed engines as well when I have a separate starter button I don’t know who invented this key switch start thing but I hate it. For example how in the heck are you supposed to crank a loaded engine through with the throttle open and the mixture lean with the mags off It looks to me like a combination of slick marketing and security theater in that having a key is somehow supposed to keep people from stealing airplanes. That said I also hate cars with a new computer style on off button. it strikes me as one more way to remove competence - and responsibility- from people. Crabbiness aside I’d like to wish everybody a joyous Easter
 
cgoldy said:
So just to recap. Last month before I replaced my heavy borer with the whirlwind and lead acid with an earthex and moved the battery location from rear seat to fire wall, she would start on the second or third blade religiously.
Click to expand...
Colin, That is why I said in post#14 that it is turning too fast for the impulse to do it's job. Try exchanging the P leads on the back of the mag switch so that the mag is shut off and the Pmag is on during starting.


WhiskeyMike said:
. I don’t know who invented this key switch start thing but I hate it.
Click to expand...
This key start thing showed up when they started using the "shower of sparks" for starting instead of impulse couplings. They wanted to ensure that one mag was dead and that the "shower of sparks" was properly turned on only while the starter was engaged.
 
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