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need help installing mags!

Posted: Thu Dec 28, 2006 6:50 pm
by rjonesboy
can someone please tell me the procedure for installing mags in a 470 GPU. I changed cylinders and mags onto a different engine and dont know how to time the mags. Stock 220 block with 470 domed pistons and dual mags if that helps. I can find TDC and I know the gears in the mags are marked, but I need to know how and when to put them in and how to set the timing. I hope this makes sense. Thanks in advance

Posted: Thu Dec 28, 2006 7:30 pm
by Des Moines Boater
Make sure when you find top dead center that you are on the compression stroke. Put your finger over the spark plug hole as you rotate the prop. When it blows air past your finger you are coming up on the compression stroke. Slowly bring it up to top dead center and mark the flex plate or something. Now back the prop up 20 degrees and mark that spot. You want the prop to be set at 20 degrees before top dead center.

Take the 5/8 inch plug off the mag so you can look inside and see the white plastic gear. Turn the mag until you have the red gear tooth centered in the middle. Put the mag on and bolt it down. Leave it loose enough to turn slightly. Connect your timing buzz box to the P-lead and set the mag so the light goes out just as you come up on the 20 degree mark.

If you have an impulse mag be sure to rotate past the point that the mag clicks. Then back it up a little and pull it back to the 20 degree point. Make sure you have the gear lash out by pulling in the direction of rotation. If you go past the mark back the prop up a little and pull it slowly back up to the mark. That will get rid of the gear lash.

If you're a Lycoming guy, don't forget the number one cylinder is furthest away from the prop on the Continental. Check the case marking.

Posted: Thu Dec 28, 2006 7:50 pm
by Root Pass
I would love to have an aircraft motor someday but boy that kind of stuff sounds complicated.

Posted: Thu Dec 28, 2006 7:59 pm
by PredatorI0540
Boblee, it really isnt all that hard to do. Just gotta be half ass mechanical :lol:

Posted: Thu Dec 28, 2006 8:08 pm
by Root Pass
I guess it sounds foreign if you haven't been around them. :oops: I've worked on farm trucks and tractors out here forever but have only recently been around aircraft engines.The ones I saw at Operation Airboat were impressive.

Posted: Thu Dec 28, 2006 8:38 pm
by Olf Art
Boblee, if you can make a farm tractor run you can work on an aircraft motor.
They're both slow turning torque motors. The beauty of an AC motor is that they don't even need a battery to run. I think they're amazing.
Don't be intimidated by them.


Posted: Fri Dec 29, 2006 6:55 am
by rjonesboy
Thanks Des Moines, I have done everything you said. I have heard 20,25 and 30 degrees though. The problem I'm having is in setting the timing. Probably sounds stupid but I have no idea what a timing buzz box is. Can you elaborate?

Posted: Fri Dec 29, 2006 7:50 am
by pirate
If you're a Lycoming guy, don't forget the number one cylinder is furthest away from the prop [quote]

Not trying to be a smart a** but according to my Lycoming Overhaul Manual, due to the staggered configuration of the cylinders, # 1 clyinder is always the one closest to the prop on either the 4, 6, or 8 cylinder Lycoming engine.

In case anybody needs it I'd be happy to scan and e-mail any timing info.


Posted: Fri Dec 29, 2006 8:44 am
by Des Moines Boater
Pirate, you are correct on the Lycoming number one cylinder being closest to the prop. The Continental is is furthest from the prop. The caution I was giving is to look out for that difference. rjonesboy is working on a Continental. Just check the markings on the side of the case to be sure.

rjonesboy, Aircraft Spruce has the timing light/buzz box. Part number: 12-16901 DUAL MAG SYNCHRON W/ TWEETER $40.00

The numbers 20, 25 and 30 degrees before top dead center are all correct depending on your set up. I don't know the specifics of your engine but 20 to 25 should get you in the ball park.

boblee74, I didn't mean to make it sound hard to do. Basically bring the engine to 20 degrees BTC, turn the mag gear to its timing mark and put the mag on the engine. The buzz box is for fine tuning the timing.

Posted: Fri Dec 29, 2006 7:42 pm
by FP1201
Not that it's really relivent but to time the mag on a "Farmall" you retard the mag all the way back, then bar the engine until the timing mark is aligned with the flywheel, then slowly advance the mag until the impulse coupling releases then lock it down. Word of warning: Do not have you hand over a wireless cap when it releases. AMHIK :shock: