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Adjusting Magneto Timing

CharlieWaffles

CharlieWaffles

Well Known Member
So I've read the lycoming manual for verifying the magneto timing and watch several videos that other threads recommended. There is only one part that isn't clear to me.

I have found the TDC for the compression stroke for #1, and backed off to the 25 degree mark (per my data plate). I hook up my buzz box and found that my right mag (both are slick magnetos, left is a retard). is firing at 28 degrees - so definitely a little early.

I loosen the magneto hold down nuts enough to be able to rotate the magneto a little to adjust the timing. Here is where my question comes in:

Does it matter which direction I rotate the magneto?

I know there are left and right turning magnetos and they are referred to from the drive end. I forgot to look to see what my magneto was placarded. Assuming the right side magneto is right turning, then I should rotate the magneto housing clockwise when viewed from the distributor end of the magneto correct (counter-clockwise when viewed from the drive end/propeller side)? Or does it not matter when adjusting the timing like this? I haven't been able to figure out if the right/left turning only matters when installing a timing pin for installation into the engine or if it matters when adjusting the timing too.
 
1. Make sure you back up the prop past the timing mark, then approach 25 degrees in the normal rotation direction. This insures you take out any slack in the gear train. If you had an impulse mag you would want to hear it snap before turning the prop back.
2. Mag direction? Just try it! Bump the mag a few degres and check timing again. If it's 30 btdc now you went the wrong way! Keep iterating until you have it at 25. Check again after tightening the hold down clamps.
 
Easy way, set your prop at 25° BTDC as Bob mentioned, then move the mags till you get the buzz. Done...
Direction doesn't matter.
 
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Bob Turner had it correct: The only way to ensure correct timing is to turn the prop in the direction of normal rotation approaching the timing marks very slowly while observing the buzz box lights.
 
Walt said:
Bob Turner had it correct: The only way to ensure correct timing is to turn the prop in the direction of normal rotation approaching the timing marks very slowly while observing the buzz box lights.
Click to expand...

Yes.

You need to take out the gear lash, or the timing will be off.
 
Exactly. I back the prop up 20-25 degrees and then move in the direction of normal rotation when checking the timing.
 
I should clarify, I back up from the BTDC (in my case 25 degrees) and then advance the prop back towards the BTDC to verify once the slack is gone.
 
Mags

The first step is to go a little past top dead center to "snap" the impulse. Then back up to 30 degrees, then normal rotation to 25 degrees, If you back up too far past 30 degrees you will reengage the impulse.
After you have retimed the mag, with the buzz box still connected, back up the prop to 30 degrees, very slowly bump the prop forward until the buzz box sounds, then recheck the degrees.
And most important, make sure you have one set of spark plugs removed.
 
The impulse issue is not an issue. All of the newer vans sold engines come with retard mags, no impulse coupling is involved with these 540s.
 
stinson pilot said:
Easy way, set your prop at 25? BTDC as Bob mentioned, then move the mags till you get the buzz. Done...
Direction doesn't matter.
Click to expand...

Same goes for the magneto, there is backlash here too so you need to move the mag in the anti-clockwise direction, I think??? I never remember and have to work it out each time.

Otherwise you will set it right and then move the prop and check it again and it will be wrong. :eek:
 
How accurate is this method?

For the impulse coupling I have always used the dot on the starter with the
corresponding timing mark on the flywheel to verify timing.
No tools needed and as stated in the Lycoming book when the impulse coupling snaps, or fires, the dot should line up within "1 to 3 degrees of TDC.
This according to the Lycoming engine manual.
 
N427EF said:
For the impulse coupling I have always used the dot on the starter with the
corresponding timing mark on the flywheel to verify timing.
No tools needed and as stated in the Lycoming book when the impulse coupling snaps, or fires, the dot should line up within "1 to 3 degrees of TDC.
This according to the Lycoming engine manual.
Click to expand...

You are assuming then that the impulse cage and stops have no wear.

May be accurate and may not.
 
Thanks again for all the help. I found my right magneto was about 3.5 degrees too early (28-29 instead of 25). The left was right at 25. I was able to rotate the right magneto and have verified multiple times (with gear slack removed) that both fire almost simultaneously right at 25 degrees.

BEFORE
20140721_223723907_iOS_zpsb4a3e4c1.jpg
 
Mag timing that changes significantly is indicative of mag problems, I consider anything over 2 degrees a potential problem. Wear on the cam block will cause late timing (moved from 25 to 23) while point wear will cause early timing (25 to 28).

These changes will also cause the internal 'E' gap timing to change making the mag less efficient (lower spark energy).
 
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Good to know. I suspect in my case since the engine was new and is now at 100 hours that it came this way from the Lycoming factory. I did NOT perform a mag timing check when I installed the engine.
 
CharlieWaffles said:
Good to know. I suspect in my case since the engine was new and is now at 100 hours that it came this way from the Lycoming factory. I did NOT perform a mag timing check when I installed the engine.
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Is there something wrong in Williamsport? My new XIO-540 also had the right mag at 28 degrees. You would think that for $40K they could time the mags. My hangar neighbor's 10 also had one (brand new) mag advanced. i'll ask him if it was the right.
 
It used to be the case that after the engine was assembled, they ran it in a test cell. The accessories (mags, etc.) used in the test run stayed with the cell, and after a test run and as being prepared to ship, they would add a couple of mags, carb, etc. to the box.

There is plenty of room here, even with an updated test cell procedure, to assume the end-user is going to check the timing before running the engine.

It's actually quite easy, and seems to me to be a very prudent thing to do.

Dan
 
DanBaier said:
It used to be the case that after the engine was assembled, they ran it in a test cell. The accessories (mags, etc.) used in the test run stayed with the cell, and after a test run and as being prepared to ship, they would add a couple of mags, carb, etc. to the box.

There is plenty of room here, even with an updated test cell procedure, to assume the end-user is going to check the timing before running the engine.

It's actually quite easy, and seems to me to be a very prudent thing to do.

Dan
Click to expand...

I agree, but interestingly checking mag timing is not in the Installation Section of the O-360 Lycoming Operators Manual I checked.:rolleyes:
 
az_gila said:
I agree, but interestingly checking mag timing is not in the Installation Section of the O-360 Lycoming Operators Manual I checked.:rolleyes:
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IMHO if Williamsport is not going to time the mags then they should ship them un-installed. Mine were on the engine, with the hold down nuts marked with torque seal. During my build I never marked anything with torque seal unless it was 'good to go'.
 
seal

BobTurner said:
IMHO if Williamsport is not going to time the mags then they should ship them un-installed. Mine were on the engine, with the hold down nuts marked with torque seal. During my build I never marked anything with torque seal unless it was 'good to go'.
Click to expand...

True, torque seal is a indication that the item has been inspected. I think Williamsport deserves a call for not following industry standards.
 
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