Stuck and need advice

My son's 6 is stuck and he is trying to get home for work tomorrow. He has been having trouble with starting recently, but noticed that letting go of the switch lets it start. I assumed a weak impulse mag, or a switch problem.
We took the Impulse magneto off of my plane and put it on his. Now the impulse mag is completely dead. It checks out fine with the squawk box, but the engine dies when the right mag is shut off.
We removed the P lead completely, but same thing. Next we took the cap and wiring harness off of my plane - no improvement. Now we have two dissembled planes, and he needs to be heading back to North Carolina.
What am I missing? How can a good mag and harness move to another plane and check out good during the timing and synchronization, but be completely dead when running?

Thank you!

Clean spark plugs?

Bad switch?

Probably not timed correctly when you installed it (the mag and/or eng not on cyl 1 when installed).

Kyle Boatright said:

Bad switch?

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That would be my guess as well.

Could try hand propping it, or put it in ?both? and rig a separate starter switch.

I had an old Volkswagen that did that. Crank and crank, and then as soon as you let it off the ?start? position she would fire. I wired in a separate start button.

He said he removed the P lead so currently he has a timing problem, probably out 180 degrees.

Timing issue. 180* off on the roter (#1 at TDC on exh, not compression stroke) can fool you as the impulse will still snap in the correct place and buzz box will show correct timing, yet all cylinders won't fire, at least not when there is compressed fuel/air in them.

Always pull the top plug on #1 and put your thumb over the hole. As you swing the prop towards TDC, your thumb should be pushed away from the hole. If it doesn't, swing the prop around another 360* If your son doesn't have a plug socket, you can pull the rocker box cover and observe the rockers to determine power vs exhaust stroke.

Not to insult your experience, but did you use a pin in the cap area? Two keys with mags: #1 at TDC on compression stroke, not exhaust stroke and rotor must be placed/locked in #1 firing position position with a pin. Many get confused with the fact that a mag runs 1:1 with engine revolution. However, it has a 2:1 reduction gear driving the rotor. Therefore the rotor turns at half crankshaft speed, just like an automotive distributor. You can't just stick it in the engine and rotate it until the buzz box goes off. Only a 50% chance that it will work.

Larry

Probably mis-timed mag is why it won't fire.

But as for the key switch, wasn't there a bad batch of ACS key switches a while back? The trick to making them work (at least temporarily) was to turn the key only far enough to get the starter to turn on and no further. If you turned the key all the way to the stop, both P-leads would be grounded.

Thank you all - The problem is fixed and he departed at 5:00am. He should make it to work on time.
I honestly don't know what the cause was, but either the internal timing was off or the engine was not at 25BTC when we installed it. The issue is that we had installed and re-installed 3 or 4 times while troubleshooting. I can not for the life of me understand how we would have repeated our mistake that many times in a row, but I guess that is what you get when you work 3 days in a row until 3:00am trying to do a 20 minute job. We decided to take a break - which is when I sent out the help request. After a break we were able to think straight and re-do it properly. - what a frustrating weekend, but it is so rewarding that the original hard-starting problem is resolved. it was as original suspected: a weak impulse magneto.
Thank you again for the help!

lr172 said:

Timing issue. 180* off on the roter (#1 at TDC on exh, not compression stroke) can fool you as the impulse will still snap in the correct



Not to insult your experience, but did you use a pin in the cap area? Two keys with mags: #1 at TDC on compression stroke, not exhaust stroke and rotor must be placed/locked in #1 firing position position with a pin. Many get confused with the fact that a mag runs 1:1 with engine revolution. However, it has a 2:1 reduction gear driving the rotor. Therefore the rotor turns at half crankshaft speed, just like an automotive distributor. You can't just stick it in the engine and rotate it until the buzz box goes off. Only a 50% chance that it will work.

Larry

Click to expand...

Be careful here. #1 needs to be at the firing position, not TDC, when installing the mag. Usually you find TDC, and then turn the prop backwards to the 20 or 25 DEGREES BTDC and then install the mag, which if you have the pin inserted correctly, it is ready to fire.

Vic

Mags

Two issues for the "next guy". First the op made no mention of mag manufacturer???
Second, the importance of determining that the MAG is positioned to the #1 firing position. Then rotate the mag gear counterclockwise to "snap" the impulse, then clockwise to the point where the mag fires with the impulse disengaged. With
Slick this is where the timing pin is engaged. With Bendix you can either use a special lock to keep the mag from rotating, or depend on care and some good luck to get the mag in place without rotating the gear. Difficulty to do the latter in tight space.
Many do not like the locking device for the Bendix mags. It does require a lot of care to be sure no rotational load is put on the rather fragile internal gear.