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Ignition timing

Dorfie

Well Known Member
Engine is IO-540-C4B5.
Viewing engine from behind, which direction do you turn the magnetoes (L+R) to advance the timing?
About how much magneto movement is 1 degree?
Thanks.
Johan
 
Get some help with this, please... if you're asking this question, let someone show you how before you add to your issues. Even licensed AMTs take training, and need the specific tools -- have seen turbine mechs screw timing up.
 
With the mag nuts only snug and the engine at the 25* mark or wherever you want it to spark, rotate the mag and listen. The buzz box only buzzes when the points are open. THerefore - no buzz is BEFORE ignition event and buzz is AFTER ignition event.

Mag spins same direction as crank, so rotating mag in the opposite direction should advance timing. Usually you have to go back and forth a bit to get it to start buzzing right at the mark you want. It's trial and error. Always pull the prop back and advance again to the mark, to insure it starts buzzing right on your mark

Please don't try to advance ignition without some type of timing indicator/buzz box.

Larry
 
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Timing

OP says RV10 flying. If the engine has been run I like to start out with a new gasket, two new gaskets with impulse. This eliminates the possibility of tearing the gasket and creating an oil leak.
The OP's question is indicative of someone who should not be doing this without some qualified help.
Inadvertently getting the timing too far advanced could cost a lot of money.
 
Help

Dont just twist and turn the mag until the sounds change. I learned in A&P school, you must turn the mag in the proper direction so that the gear backlash is taken up. It is not just twist and turn. Tjhere is a step by step process that works every time. Let an A&P show you how, it is worth a $150 tip for a lesson.
 
Piling on

Don't forget, assuming an impulse coupling, make sure you clear the retard point first. etc. etc. etc.

I saw this yesterday and was reluctant to reply. It's already been mentioned and can't be emphasized enough. If you have to ask such a broad question, it's even more important to get help and instruction from someone with the proper skillset.

Everyone here had mentors that they learned from as well as some self-taught, potentially very expensive lessons. Regarding the latter, learn the lesson from my pain.
 
Looking from the pilot seat the mags rotate counter clockwise (or anti clockwise) or to the Left. To advance the timing rotate the magneto housing in the direction of rotation (counter clockwise); to retard, roll it clockwise. With a buzz box it is easy to 'discover' this yourself. Even easier is to look at the data plate on the magneto, or the Lycoming diagram, which I'll post as soon as I figure out how...There we go. Green arrow is advance, red is retard. I agree with others that simply rotating the magneto without some timing apparatus (buzz box) is a bad idea, but wanted to answer the question.


wiring2.jpg

==dave==
N102FM
 
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Looking from the pilot seat the mags rotate counter clockwise (or anti clockwise) or to the Left. To advance the timing rotate the magneto housing in the direction of rotation (counter clockwise); to retard, roll it clockwise. With a buzz box it is easy to 'discover' this yourself. Even easier is to look at the Lycoming diagram, which I'll post as soon as I figure out how...There we go. Green arrow is advance, red is retard. I agree with others that simply rotating the magneto without some timing apparatus (buzz box) is a bad idea, but wanted to answer the question.


View attachment 13711

==dave==
N102FM

On a mag, the rotor turns in an opposing direction from the main shaft (no idler gear), where advance is set. Mag shaft spins in same rotation as cramk (there is an idler gear between crank and mag gear), but the rotor, controlling spark distribution, spins in the opposite direction.
 
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That's good to know...

As to your second question -
I haven't measured it, but I would estimate the diameter of the magneto housing at the lip that sits on top of the accessory case is about 4 inches, or 100mm. That would mean a circumference of 314mm, so a degree would be a little less than a millimeter of movement at the housing edge. Interesting as an academic question, but not the best way to adjust timing in and of itself.

==dave==
N102FM
 
On a mag, the rotor turns in an opposing direction from the main shaft (no idler gear), where advance is set. Mag shaft spins in same rotation as cramk (there is an idler gear between crank and mag gear), but the rotor, controlling spark distribution, spins in the opposite direction.

Larry,
Thank you very much for answering the question. It is the direction of rotation of the rotor on which the cam lobes are and also controlling the spark distribution that I was after. That makes direction of timing advance/retard clear.
Much appreciated.
Johan
 
Larry,
Thank you very much for answering the question. It is the direction of rotation of the rotor on which the cam lobes are and also controlling the spark distribution that I was after. That makes direction of timing advance/retard clear.
Much appreciated.
Johan

The mag main shaft (which controls the points and therefore timing) turns the same direction as the crankshaft AND the camshaft. The rotor spins opposite of all those.

Larry
 
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