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12-23-2013, 07:44 PM
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Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 9,035
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A traditional and typical shower of sparks mag has a second set of retard breaker points that need to be switched to during cranking of the engine to start.
This is typically done using one of the "extra" terminals on the back of the traditional key switch that we don't use with impulse coupling mags.
If a toggle switch is being used to control the SOS mag, it is likely that the even if engine is being started with only the left mag. active, the engine is still being started without retarding the timing. This does have a danger of kick back.
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Opinions, information and comments are my own unless stated otherwise. They do not necessarily represent the direction/opinions of my employer.
Scott McDaniels
Van's Aircraft Engineering Prototype Shop Manager
Hubbard, Oregon
RV-6A (aka "Junkyard Special ")
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12-23-2013, 07:53 PM
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Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 9,035
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Quote:
Originally Posted by Mike S
I see no reason to start on left only in your case---------as at cranking speeds the right mag is not doing much of anything in the spark department, unless it also has a SOS or impulse coupling-----just not enough electrical energy developed in the mag at cranking speed. It will not hurt to start left only if it is the only mag with the shower of sparks setup.
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Not entirely true mike.
You are correct that without the snap of an impulse coupler, the spark is weak, but it is still strong enough to cause a problem. Especially with the fast spinning starters that we typically use now a days.
This weak spark is not retarded in timing (not good).
This is why the traditional keyed start switch has a location for a grounding plate so that the right mag (if it is a non impulse mag) is disabled while cranking in the start position. If both mags are impulse, then the grounding lug is left off so that both are enabled during start.
__________________
Opinions, information and comments are my own unless stated otherwise. They do not necessarily represent the direction/opinions of my employer.
Scott McDaniels
Van's Aircraft Engineering Prototype Shop Manager
Hubbard, Oregon
RV-6A (aka "Junkyard Special ")
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12-25-2013, 10:30 AM
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Join Date: Jan 2007
Location: Picton, Ont., Ft. Myers, Fl
Posts: 294
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yesterday
I did 4 starts yesterday, all using L mag only for start and I feel that it cranks smoother using only the left, still starts quickly.
Thanks for numerous enlightening responses. 
Enjoy the holidays!!
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Dave Main
Membership due Oct., 2020
RV-4 0-360-188 Catto 3-blade C-FTDQ...
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12-25-2013, 11:06 AM
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Join Date: Feb 2006
Location: Valley Forge, Pa
Posts: 636
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Shower of sparks
May I ask is this a 0-360A1D out of a Mooney? If so there is a switch for this application and one of the two mags has a extra set of retarded points for starting.
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12-25-2013, 11:18 AM
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Join Date: Jan 2007
Location: Picton, Ont., Ft. Myers, Fl
Posts: 294
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Mooney
YES, it is an A1D out of a Mooney!
Can you elaborate on the switch? The left mag has a "shower of sparks" label on it. Not the right.
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Dave Main
Membership due Oct., 2020
RV-4 0-360-188 Catto 3-blade C-FTDQ...
Last edited by 777Dave : 12-25-2013 at 11:20 AM.
Reason: additional
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12-25-2013, 02:35 PM
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Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 9,035
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Quote:
Originally Posted by 777Dave
YES, it is an A1D out of a Mooney!
Can you elaborate on the switch? The left mag has a "shower of sparks" label on it. Not the right.
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As I mentioned in post 11, if the shower of sparks mag is a retard breaker magneto (I think they all are but can't say for certain), it requires the use of a traditional keyed ignition switch for the timing to be retarded during start.
The retard breaker points are a second set of points inside the mag that is positioned so they open later in rotation which retards the firing of the magneto while cranking for start.
The keyed ign. switch is wired in a way that switches between the two sets of breaker points depending on whether it is in the start (cranking position) or the both position.
A retard breaker mag should have two P lead connections on it.
I suspect that your starting vibrator is being switched on by your start toggle switch, but if the left mag is only controlled by a single toggle, it is likely that it is not being switch into retarded timing mode while cranking... danger of kick back.
A quick google search found THIS explanation by John in the Sacramento Sky Ranch manual (see page 45).
__________________
Opinions, information and comments are my own unless stated otherwise. They do not necessarily represent the direction/opinions of my employer.
Scott McDaniels
Van's Aircraft Engineering Prototype Shop Manager
Hubbard, Oregon
RV-6A (aka "Junkyard Special ")
Last edited by rvbuilder2002 : 12-25-2013 at 02:45 PM.
Reason: added link
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12-25-2013, 07:02 PM
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Join Date: Jan 2007
Location: Picton, Ont., Ft. Myers, Fl
Posts: 294
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I think I will have to look closer at the switch wiring. Thanks for the great link.
This is what my mag selector switch looks like.
http://s7.photobucket.com/user/idleo...]=1&sort=1&o=0
Anyone recognize its origins?
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Dave Main
Membership due Oct., 2020
RV-4 0-360-188 Catto 3-blade C-FTDQ...
Last edited by Mike S : 12-26-2013 at 11:07 AM.
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12-25-2013, 09:25 PM
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Join Date: Feb 2006
Location: Valley Forge, Pa
Posts: 636
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0-360A1D shower of sparks
This system has a vibrator box on the firewall,One of the two mags will have two leads coming off the back,this is the one containing the retarded points for starting,you can find these switches on ebay from time to time.The good thing about this engine is its an easy conversion to Pmags as you have two good drive gears and mounting studs are the right length,something to think about at rebuild time.
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12-26-2013, 10:53 AM
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Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 9,035
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Quote:
Originally Posted by 777Dave
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I don't recognize it... looks very old and not likely compatible with a SOS mag.
The simplest process for you to evaluate your system at this point is to just look at the mag that says shower of sparks. Does it have a P-lead wire connected to each of the two terminals on the mag.? If not, then you are for sure starting without the mag timing being retarded (regardless of what procedure you use) and are at a high risk for kick back. If there is a wire connected to each of the two terminals, then you need to do further investigating to determine what means (if any) is being used to switch between the two sets of breaker points when cranking or in normal run mode.
__________________
Opinions, information and comments are my own unless stated otherwise. They do not necessarily represent the direction/opinions of my employer.
Scott McDaniels
Van's Aircraft Engineering Prototype Shop Manager
Hubbard, Oregon
RV-6A (aka "Junkyard Special ")
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12-26-2013, 04:25 PM
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Join Date: Nov 2010
Location: Australia
Posts: 53
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That magneto selector switch looks very similar to what is in my Yak-52. It has a shower of sparks on the left magneto. Starting technique on the Yak is to hold the starter button in with the magnetos on '0', then after the engine kicks, flick the Maggies to both, then release the starter button. The shower of sparks is engaged by holding the starter button in. Perhaps you have a similar setup?
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