Do mags turn same as prop?

[Mcstealth]

Sorry for the rookie questions. Do the mags turn the same direction as the prop? Evidently it makes a difference with how to wire and time the engine. 0-320, 150hp. Slick Mags. 

[EricJ]

Depends on how the accessory case is geared and the configuration of the engine.   This is why there are L and R mags (in the part number, not the location on the engine).   The engine overhaul manual or similar documentation should show the wiring diagram for the specific engine like what you've included.

[Mcstealth]

0.2.2 ROTATION, LAG ANGLE AND RETARD ANGLE Rotation

Rotation specifies the direction in which the magneto rotor shaft turns when viewed from the mounting end of the magneto. Left-Hand Rotation is counterclock-wise when viewed from the magneto-mounting end: Right-Hand Rotation is clockwise when viewed from the magneto-mounting end. Important: Check the data plate on the magneto being replaced for the shaft rotation. Replace with a magneto having the same rotation.

 

I found this while researching. It doesn't tell me which way the mags turn on my particular engine though. I will see if I can get a picture of the data plate from the mag without removing them from the airplane. That's my plan at least. 

[PT20J]

According to the Specification section in the O-320 Operator's Manual, the magnetos rotate clockwise (viewed from the rear of the engine) and the firing order is 1-3-2-4. This is the standard firing order for all clockwise rotating Lycoming 4-cylinder engines.

I believe the confusion is that Lycoming made some counterclockwise rotating engines such as the LIO-320 used in twins to avoid having a critical engine and in these engines the firing order is 1-4-2-3. Lycoming  apparently used the same diagram that you posted in both the IO-320 and O-320 Operator's Manuals. I don't believe there is such a thing as a LO-320.

Skip

[EricJ]

4 hours ago, Mcstealth said:

0.2.2 ROTATION, LAG ANGLE AND RETARD ANGLE Rotation

Rotation specifies the direction in which the magneto rotor shaft turns when viewed from the mounting end of the magneto. Left-Hand Rotation is counterclock-wise when viewed from the magneto-mounting end: Right-Hand Rotation is clockwise when viewed from the magneto-mounting end. Important: Check the data plate on the magneto being replaced for the shaft rotation. Replace with a magneto having the same rotation.

 

I found this while researching. It doesn't tell me which way the mags turn on my particular engine though. I will see if I can get a picture of the data plate from the mag without removing them from the airplane. That's my plan at least. 

If you have Bendix magnetos the L or R will be in the part number for the magneto (e.g., D4LN, the 'L' means it is left).  There are several places where you could look for the part number of your magneto(s).   The IPC/Parts Manual for your airplane, or the various manuals for your engine.    For slick magnetos it'll be marked on the data plate whether it is R or L, but it will be consistent with any Bendix mag that can be used on the same engine.   So if you find a part number that says a Bendix L mag fits a particular engine, then the appropriate Slick mag will also be L.

[Mcstealth]

1 hour ago, EricJ said:

If you have Bendix magnetos the L or R will be in the part number for the magneto (e.g., D4LN, the 'L' means it is left).  There are several places where you could look for the part number of your magneto(s).   The IPC/Parts Manual for your airplane, or the various manuals for your engine.    For slick magnetos it'll be marked on the data plate whether it is R or L, but it will be consistent with any Bendix mag that can be used on the same engine.   So if you find a part number that says a Bendix L mag fits a particular engine, then the appropriate Slick mag will also be L.

I need an amended to my previous description. When I discovered the issue, I described the symptom as a "backfire."  I still stand by that. Now that I swapped the leads on the left side of the engine, I ammendment the description of the symptoms to "hesitation."  

I am going to confirm the timing on the mags as a matter course. I am suspicious as to the accuracy. 

Now I have a different question. What does LAG mean? It is on both plates of the mags. One LAG says "0" and the other says "25." Both are marked "L"

 

Edited January 31 by Mcstealth

[EricJ]

Lag is the timing change for starting.    You have 25 degrees lag on one, which would put the starting spark at about TDC, which is correct.   The other is zero, and it should be the mag that isn't used for starting (probably the right mag).

 

[Mcstealth]

1 hour ago, EricJ said:

Lag is the timing change for starting.    You have 25 degrees lag on one, which would put the starting spark at about TDC, which is correct.   The other is zero, and it should be the mag that isn't used for starting (probably the right mag).

 

I will check tomorrow to see which mag is where. Almost embarrassed to say I can not remember right now.

[Mcstealth]

19 hours ago, EricJ said:

Lag is the timing change for starting.    You have 25 degrees lag on one, which would put the starting spark at about TDC, which is correct.   The other is zero, and it should be the mag that isn't used for starting (probably the right mag).

 

So yes. The co-pilot mag is the one with the '0' Lag on the plate.