#2 firing when #1 should

[1524J]

We finally finished the annual and attempted to start the engine. No joy. Figured out the #2 cylinder is firing just after TDC. Everything is timed properly. The only issue I can think of that would cause this would be the distributor cap wires are backwards. I didn't send in the cap when I had the mag overhauled. When we were putting it back together it was really difficult to get a hand in to attach the cap wires to the mags. Would this cause the problem? Tried calling Aaron at Aircraft Select but couldn't get a hold of him. It's the dual mag. Thanks!!

[N201MKTurbo]

The mag is installed on the wrong stroke.

make sure the #1 cylinder is TDC on the compression stroke and the red tooth is in the hole.

sorry you have to take it off again

[1524J]

That's the first thing we checked. I even checked with a flashlight to make sure I could see the piston coming up in the cylinder. Pulled the top and side plugs on the mag. The "K" is just off center with the "L" more prominent than the "R". Red tooth on the mag is visible in the left side plug. Right side is difficult to get too. My IA is stumped. Got a hold of Aaron at Aircraft Select and he basically said the same thing. We have to be on the exhaust stroke. On the exhaust stroke the piston would be at the bottom of the cylinder. The piston is coming up in the cylinder and right at TDC or just a hair past the inpulse coupling snaps and I get fire on the #2 cylinder. Left front cylinder. Unless I'm losing my mind....which is possible. Rotating the prop counter-clock wise if facing the prop looking towards the plane.

I'm timing based on the marks on the flywheel being centered with the split in the case at the top of the engine.

[Guest]

With the upper plug removed from #1 turn the propeller until you feel that it's on the compression stroke, using the tip of a ball point pen through the plug hole you should be able to feel the piston at top centre.  How does this match the flywheel timing marks?  It is possible to have the flywheel installed on the wrong crankshaft bushing.  If the TDC mark agrees with piston location you have the mag installed wrong.

Clarence

[1524J]

2 hours ago, M20Doc said:

With the upper plug removed from #1 turn the propeller until you feel that it's on the compression stroke, using the tip of a ball point pen through the plug hole you should be able to feel the piston at top centre.  How does this match the flywheel timing marks?  It is possible to have the flywheel installed on the wrong crankshaft bushing.  If the TDC mark agrees with piston location you have the mag installed wrong.

Clarence

With the upper plug removed on #1 and the piston at TDC the mark on the flywheel splits the case line at the top of the engine. I can reverse the prop (clockwise 1/2 turn) then when pulling back through, right at or just after the TDC mark on the flywheel, the inpulse coupling snaps and I get fire at the #2 cylinder. On both top and bottom plugs which tells me both mags are working. The mag is installed with the manufacturers plate on top, just as it was pulled. Aaron asked about that. The "K" is just off center at 25 degrees before TDC with the "L" more prominent in the window than the "R". Aaron also said this is how it should look as the left mag fires first. Red tooth visible in the left side plug hole at 25 degrees before TDC.

The only issue I'm not fairly certain of is the cap wiring form the distributor to the mag. Aaron did say this could cause problems, but not what I'm seeing. Is it possible for the mag itself to be reversed?

With the #2 cylinder firing in place of the #1 it would seem I'm off 180 degrees with a firing order of 1,3,2 and 4.

I'll take pics tomorrow.

[N601RX]

It sounds like your on TDC of the exhaust stroke. To be sure your really on the compression stroke put your finger over the hole and the pressure should push it away as the piston comes up. You will need to remove the mag and rotate the prop 360 deg if this is not correct. If the mag has been disassembled they may have got the internal large gear off by 1/2 turn also.  With the lock pin in the correct (left) place the button finger should be pointed to deliver spark to #1.  

 

[1964-M20E]

If nothing else has changed but R&R the mag the it is in the mag and timing.

Could it be possible the mag shop installed something out of sync in the mag itself???

I had a governor IRAN and the prop shop installed the top part of the governor 180 degrees out and there is no way it would work.  Everyone makes mistakes.

 

 

[Mcstealth]

I suggest you go to an Oncologist right away if Two is firing and not one. 

 

[Guest]

20 hours ago, 1524J said:

With the upper plug removed on #1 and the piston at TDC the mark on the flywheel splits the case line at the top of the engine. I can reverse the prop (clockwise 1/2 turn) then when pulling back through, right at or just after the TDC mark on the flywheel, the inpulse coupling snaps and I get fire at the #2 cylinder. On both top and bottom plugs which tells me both mags are working. The mag is installed with the manufacturers plate on top, just as it was pulled. Aaron asked about that. The "K" is just off center at 25 degrees before TDC with the "L" more prominent in the window than the "R". Aaron also said this is how it should look as the left mag fires first. Red tooth visible in the left side plug hole at 25 degrees before TDC.

The only issue I'm not fairly certain of is the cap wiring form the distributor to the mag. Aaron did say this could cause problems, but not what I'm seeing. Is it possible for the mag itself to be reversed?

With the #2 cylinder firing in place of the #1 it would seem I'm off 180 degrees with a firing order of 1,3,2 and 4.

I'll take pics tomorrow.

The magneto case has two small alignment marks cast into the case near the flange for the cap.  The harness housing has two similar alignment marks cast into it, they must be aligned for correct firing order.

Clarence

[1524J]

So we think we've solved the problem. I'll attach pics so if anyone else runs into this, you'll have a reference. 

#1 Cylinder with the piston at the top of the compression stroke. It'll look the same if your on the exhaust stroke so you need to feel for pressure.

Pic showing TC mark splitting case line...maybe not perfect but I wasn't setting the timing.  You have to zoom in to see the mark.

Window in the middle of the mag. You can see the start of the "L" in the center. "K" is just to the right. 

 

This is a shot of the left side window of the mag and where we think the problem lies. If you zoom in, you'll be able to see a red dot on the backside of the tooth. That dot should be 180 degrees and is NOT the red tooth that's supposed to be in the window.

Courtesy of Aaron at Select Aircraft, this is the red tooth you should see. 

Soon as I get a chance I'll try to fix the problem and report back. If you get a mag returned and it's just a red dot in the side window your firing order will not be correct.....at least I'm hoping this will solve it.

Thanks to all who replied!!!

[N201MKTurbo]

If you put the cap on upside down it will still work, your top and bottom plugs will be swapped from what you expect. If you put the mag on upside down it will work. You can trouble shoot a mag vs harness problem by doing that. If the problem stays the same it is the harness, if it moves to the other mag , it is the mag.

[carusoam]

Great photographs, 24J!

The power of MS continues to impress.

Best regards,

-a-

[Dale Logsdon]

Your pictures show that the mag is not timed correctly to the engine.

The distributor gear (with the red dot and red tooth) turns at 1/2 the rotations of the drive gear.

If you remove your mag and then rotate the mag drive shaft 1 complete turn the proper red painted tooth on your distributor gear will be in the window where it should be.

this will put your mag in the proper rotation  to install back on the engine.

 

[1524J]

It's amazing how quickly an IO-360 will start when the mag is timed properly to the engine.  

Thanks again to everyone that responded.....and to Aaron at Aircraft Select for having patience with me and helping me figure out a red dot does not equate to a red tooth. 

[carusoam]

I think a few of us have learned along with you of dot vs. tooth.

I'm glad you shared the details.

Best regard,

-a-