Left/Right magneto = top or bottom plug?

John Richardson

John Richardson

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John Richardson
On a lycoming 0-540, which magneto powers the top plug on cylinder #6, and which powers the bottom plug?

I can trace the lead, but I’m not sure which magneto is considered “left” or “right”.
 
Which is a stupidity I've fought against for fifty years. "Port" and "Starboard" should take care of that little problem, shouldn't it? Same for "right wing" and "left wing" and all of the other "left" and "rights".

Don't tell me there is a standard. I've looked for years and haven't found one.

Jim
 
John Richardson said:
On a lycoming 0-540, which magneto powers the top plug on cylinder #6, and which powers the bottom plug?

I can trace the lead, but I’m not sure which magneto is considered “left” or “right”.
Click to expand...

1. 2. 3. 4. 5. 6.
Top. L. R. L. R. L. R.
Bot. R. L. R. L. R. L.

does that help? 10% chance someone wired your backwards...

Paul
 
If I recall.....the wiring harness is marked. Each lead for each mag.....
 
I think he asked, ‘which mag is L and which is R?’.
As in, it seems he is unsure if that means looking at the engine from the cockpit or the propeller.
If so, it is from the cockpit.
I am unsure about pusher a/c however.
 
You gotta explain that one to me. The only difference between the two diagrams is that in one the top plugs use solid lines and in the other the bottom plugs use solid lines.
 
Silvaire said:
You gotta explain that one to me. The only difference between the two diagrams is that in one the top plugs use solid lines and in the other the bottom plugs use solid lines.
Click to expand...
Hm. Didn't catch that. Probably an error that Lycoming has never corrected.
 
Right and left as seen from the pilot's seat. I have seen ignition wires in all sorts of configurations.
 
Silvaire said:
You gotta explain that one to me. The only difference between the two diagrams is that in one the top plugs use solid lines and in the other the bottom plugs use solid lines.
Click to expand...

The dashed lines are bottom plugs, the solid lines are top plugs.
 
Silvaire said:
You gotta explain that one to me. The only difference between the two diagrams is that in one the top plugs use solid lines and in the other the bottom plugs use solid lines.
Click to expand...
Or the bottom plugs are the dotted lines in both.
 
smv said:
The dashed lines are bottom plugs, the solid lines are top plugs.
Click to expand...

Where did you get that? It doesn’t say that anywhere in the text. There’s no legend for the figures.
 
Dan Thomas said:
And the manual itself says nothing.
Click to expand...
FWIW: It's my understanding the dotted lines and dotted lead connectors represent "hidden" items that run below the cylinders/baffling, i.e., the ignition leads to the bottom plugs. Some Lycoming books do a better job at the difference.
John Richardson said:
which magneto powers the top plug on cylinder #6, and which powers the bottom plug? [...] I’m not sure which magneto is considered “left” or “right”.
Click to expand...
As to which mag powers the top or bottom plug will depend on which routing option was selected when the ignition leads were installed. See the diagrams in Post 7. On which mag is considered the LEFT or RIGHT, here it is straight from the book...
upload_2020-6-23_12-25-7.png
 
John Richardson said:
On a lycoming 0-540, which magneto powers the top plug on cylinder #6, and which powers the bottom plug?

I can trace the lead, but I’m not sure which magneto is considered “left” or “right”.
Click to expand...

Aren't the harness leads marked? I know its not a 540 manual...
upload_2020-6-23_13-12-5.png
 
smv said:
Logic.
Click to expand...

So what is wrong with the logic that one spark plug is above the other? They aren't side by side. Obviously they just didn't want to take the time to make a second drawing but they should have at least included a simple legend such as:

_____ top
------- bottom

Otherwise we are left having to make an assumption. You are correct however because given the choice between these two logic trees the only one that results in a solution is the one that adheres to the legend. Considering the graphics technology available at the time the Lycoming manual was printed it's likely that there probably was a legend that inadvertently got left out or cut off.
 
Silvaire said:
So what is wrong with the logic that one spark plug is above the other? They aren't side by side. Obviously they just didn't want to take the time to make a second drawing but they should have at least included a simple legend such as:

_____ top
------- bottom

Otherwise we are left having to make an assumption. You are correct however because given the choice between these two logic trees the only one that results in a solution is the one that adheres to the legend. Considering the graphics technology available at the time the Lycoming manual was printed it's likely that there probably was a legend that inadvertently got left out or cut off.
Click to expand...
You could assume the opposite and nothing would change.
 
Lindberg said:
You could assume the opposite and nothing would change.
Click to expand...

Yes, that was my point. Given the figures as they are presented with no other information the first "logic" that I would apply is that since the spark plugs are depicted vertically in the pictures then the upper one must be the top and the lower one the bottom. But using that logic there is no solution, the two diagrams are identical. So if you use the solid vs dashed line logic you end up with the two opposite configurations but you still have to make an assumption as to weather the solid or the dash equates to the top plug. Do you toss a coin?
 
Silvaire said:
the two diagrams are identical
Click to expand...
They aren't. The solid and dashed lines are inverted.
you still have to make an assumption as to weather the solid or the dash equates to the top plug
Click to expand...
You don't because it doesn't matter. Whichever way you decide to read the diagrams, they give the same two options. In both drawings, no matter which set of lines is top or bottom, each mag goes to top plugs on one side and bottom plugs on the other. The second diagram is simply the reverse of however you read the first diagram.
 
Lindberg said:
... Whichever way you decide to read the diagrams, they give the same two options. In both drawings, no matter which set of lines is top or bottom, each mag goes to top plugs on one side and bottom plugs on the other...
Click to expand...

Ahh I get what you are saying. They are two alternatives, there is no right or wrong, you can do it either way so it doesn’t matter what you think the solid or dashed lines mean.
 
Silvaire said:
Ahh I get what you are saying. They are two alternatives, there is no right or wrong, you can do it either way so it doesn’t matter what you think the solid or dashed lines mean.
Click to expand...

FYI, if you look at the OH manual, on the pervious page to where these 540 diagrams are located they cover the 4-bangers and their diagrams much more clearly show that Lycoming uses dashed lines for the bottom ignition wires and solid lines for the top wires in their diagrams.
 
Which mag(s) have an impulse coupling? Which cylinder(s) are primed?

Some 4 bangers only fire half the spark plugs during start, some airplanes only prime 1 out of 4 cylinders.
 
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