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  #1  
Old 05-13-2012, 08:54 AM
LettersFromFlyoverCountry's Avatar
LettersFromFlyoverCountry LettersFromFlyoverCountry is offline
 
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Location: St. Paul, MN.
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Default Installing mags

I'm learning -- very, very slowly -- the ins and outs of magnetos. As you know if you've followed another thread, I had an RPM problem on the TMX IO-360 and it was suggested that the mag timing was off.

A pal, using the buzz box, set the mag timing, but when we tried to fire it up on Wednesday night, the prop whirred a time or two, then hung up briefly -- apparently this is a sign of a kickback about to happen. I had whirred it a few times with the mag off with no problem.

So, it was suggested, the mag needed to be internally timed. The mag was off the engine once -- when I was trying to get access to put the AN fitting on the oil port for the cooler lines -- and I probably wasn't very careful putting it back on ... or at least as careful as I needed to be.

What's odd is that I don't remember this occurring on first start last September and it only seems to have been a problem in the few times I've started the engine this spring. (It sat all winter)

Anyway, I took the mag off yesterday and took the distributor cap off and played around a little bit. I don't have a timing pin -- I've ordered one -- but just using an LP-4 pop rivet, I turned the rotor until it dropped in. This is the orientation if got on the impulse coupling assembly. It does not appear to be anywhere near the point at which the impulse coupling begins to wind and I was under the assumption that the timing pin assures that it is.



Another question: I notice in this excellent article it says that the mag should be reinstalled like so:

First, remove the top spark plugs from all of the cylinders. Then, turn the propeller in the normal direction of rotation with your thumb over the spark plug hole on the No. 1 cylinder. When the air pressure on the No. 1 cylinder starts to build up and tries to blow your thumb off the hole, slowly continue to turn the prop until the timing mark listed on the engine data plate lines up exactly with the split line on the top of the crankcase for Lycoming engines or the split line on the bottom of the crankcase for Continental engines. Typically, Lycoming engine timing marks are located on the starter ring gear and Continental engine timing marks are located on the propeller flange.

I've been led to believe the proper spot is when the 25 degree mark on the flange is lined up with the reference hole on the starter. Which is it?

Any additional education you can contribute would be most appreciated.
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Bob Collins
St. Paul, MN.
Blog: Letters From Flyover Country
RV-12iS Powerplant kit
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  #2  
Old 05-13-2012, 09:16 AM
aerhed aerhed is offline
 
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Location: Big Sandy, WY
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Bob, the pin doesn't index at the beginning of wind-up. It indexes at point break. The case seam reference is used on some airplanes with a one-piece nosebowl. In this situation the timing marks are on the aft side of the flywheel. Timing marks on the front side are to be lined up with the index hole on the outer side of the starter housing. I've seen the instructions you just referenced before. They are generic and not very accurate. On your last thread I did a full rant about timing. Did I waste my time?
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  #3  
Old 05-13-2012, 09:24 AM
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LettersFromFlyoverCountry LettersFromFlyoverCountry is offline
 
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Quote:
Originally Posted by aerhed View Post
Did I waste my time?
Not yet.

I'm using your advice and instructions. I guess I'm asking the question: Does it look right... so far?

Don't forget: You guaranteed this.
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Bob Collins
St. Paul, MN.
Blog: Letters From Flyover Country
RV-12iS Powerplant kit
N612EF Builder log (EAA Builder log)
Last article: "Gonna Finish This Sucker" (Kitplanes)
Waiting for the avionics kit (backordered: chip shortage)
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  #4  
Old 05-13-2012, 10:19 AM
aerhed aerhed is offline
 
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Yeah, so far. If the pin is really in the hole (pop rivet is fine)and your prop is at 25 BTC, then the mag should fit in its normal postion. The only way it won't is if the mag drive gear is indexed wrong inside the accessory case. Not likely unless it got pulled out and turned. Follow my last diatribe word for word. When all is done, you should be able to back up to engage the coupling, then come forward through TDC. Your coupling should snap at TDC or a bit after center, depending on the lag angle stamped on the mag label. If it does snap in that area, then you MUST be in the ballpark to the point where you can "fine time" it. Also, if it does snap in the right area, there is no way your left mag can be causing kickback even if its off a few degrees. If you still think your getting kicked back it would have to be caused by an advanced spark from the right. That would mean the right isn't getting grounded during start. You might want to time up that left one and hard wire the right (P-mag?) so you know its turned off and start on just the left. Eliminates possibility of the P-mag being whacko.
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  #5  
Old 05-13-2012, 10:56 AM
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Question for you Bob. Are you using a key switch to start or individual toggles with a startbutton/toggle?
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  #6  
Old 05-13-2012, 11:30 AM
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I have a toggle switch for the left mag and a toggle switch for the right lightspeed and a starter pushbutton.

I haven't tried starting the engine using just the Lightspeed b/c there was a warning against doing so that came with the engine. From what someone -- I think Mahlon -- said, whatever was in the innards of the Lightspeed that might've contributed to kickback by doing so (that was the warning) has been corrected but I haven't worked up the courage yet to try it.
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Bob Collins
St. Paul, MN.
Blog: Letters From Flyover Country
RV-12iS Powerplant kit
N612EF Builder log (EAA Builder log)
Last article: "Gonna Finish This Sucker" (Kitplanes)
Waiting for the avionics kit (backordered: chip shortage)
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  #7  
Old 05-13-2012, 11:41 AM
jrs14855 jrs14855 is offline
 
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Default timing

Just to clarify a detail: the way you have the mag in the picture, hold the mag in you left hand, rotate the gear counterclockwise until the impulse snaps. The rotate CLOCKWISE slowly until the pin drops in. Finding top dead center on cylinder #1(right front) is critical to mag timing. Then turn the prop backwards slightly past the 25 degree mark, then forward again to line up the mark. The backwards and then forward is simply to take out the error from the play in the gears.
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  #8  
Old 05-13-2012, 11:43 AM
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AltonD AltonD is offline
 
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I always start on the lightspeed. I hit the starter for a couple of revolutions and then turn on the light speed. Seems to work good for me. I have the plasma on the top plugs and the mag on the bottom. The Plasma just seems to start easier. Spinning it up helps to avoid the kickback. I toasted a Skytec starter with what might have been kickback. The casting failed.
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Alton DeWeese
N526RV RV7A Tip Up, IO360 180 W/Hartzel BA prop.
Flying ~950 hours since Aug 2010
N4IDH

Construction Log
?The secret of getting ahead is getting started. The secret of getting started is breaking your complex overwhelming tasks into small manageable tasks, and then starting on the first one.?

?Mark Twain
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  #9  
Old 05-13-2012, 11:58 AM
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LettersFromFlyoverCountry LettersFromFlyoverCountry is offline
 
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I mentioned in the other thread that when I was running on both a couple of weeks ago and turned the mag off, the RPM went up. That's when the alarm bells went off.

Your set up sounds identical to mine.
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Bob Collins
St. Paul, MN.
Blog: Letters From Flyover Country
RV-12iS Powerplant kit
N612EF Builder log (EAA Builder log)
Last article: "Gonna Finish This Sucker" (Kitplanes)
Waiting for the avionics kit (backordered: chip shortage)
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  #10  
Old 05-13-2012, 12:07 PM
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Klaus talks about a mag check with a Plasma. Bottom line, you are comparing apples to oranges and the normal rules do not apply.
When I turn off the mag, I see a drop in RPM of not more than 10-20 rpm. When I turn off the plasma, I am seeing 125-150 drop. However, the engine continues to run smoothly which is the new go-no go point. I would think if the drop approached 175 rpm drop I would need to do some investigating. Basically, if anything changes from the norm, I might have a problem.
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Alton DeWeese
N526RV RV7A Tip Up, IO360 180 W/Hartzel BA prop.
Flying ~950 hours since Aug 2010
N4IDH

Construction Log
?The secret of getting ahead is getting started. The secret of getting started is breaking your complex overwhelming tasks into small manageable tasks, and then starting on the first one.?

?Mark Twain
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