'47 JD A mag timing

Bob M

Well-known Member
A friend was running his 47(?) hand start A for the first time for the season this weekend. Said it started up and ran fine for a half hour or so, then suddenly quit. After a quick inspection he noticed the magneto was loose on its mount so the drive lug had disengaged (mag mounting bolts had worked loose). He rotated the mag lug to match the drive then remounted the mag, lining up the flange back back up with the imprint in the dirt on the gov housing, then tightened it back down.

But now despite repeated attempts the engine refused to fire. Even pulling the tractor got nothing other than an occasional weak "whuff" out of the stack.

At that point asked me for help. On a whim the first thing I tried was to swap plug wires at the mag. To my delight the engine started with a single turn of the flywheel. It now seems to start and run fine.

My question: Can it be safely run it "as is", or should I retime the mag 180 deg and reverse the plug wires back to their original location?

Thanks!
 
No reason it HAS to be changed, only reason to change it could be simply not to confuse the next guy putting the wires back in it.
 
Yo Bob, what you doin messing with Deeres LOL. Indeed as the other Bob noted its okay 180 out since the plug wires are reversed but there are some who swear its better if they are correct, but I couldn't say I ever noticed a difference. That Mag, unlike an AP reduction gear drive and some others, fires at every TDC both compression and exhaust. We ever gonna meet up at shows again ????

John T
 
"<font color="#6699ff">[b:654c4848f0][i:654c4848f0]Can it be safely run it "as is[/i:654c4848f0][/b:654c4848f0]</font>"

Yes, in my opinion.

"<font color="#6699ff">[b:654c4848f0][i:654c4848f0]or should I retime the mag 180 deg and reverse the plug wires back to their original location?[/i:654c4848f0][/b:654c4848f0]</font>"

If you choose to re-install the magneto, then determine the serial number of the 1947 Model A.

The instructions to install the magneto changed with tractor 584000.

Take a look at the table below.

a168313.jpg" width="650"




Hope this helps.
 
I doubt wire location really matters ,but I would for sure check the timing ! Super easy to do on a hand start tractor. Get down eye level with the crank and watch as you turn the flywheel to see if the LH impulse dot * mark matchs up to the - mark on the side trans. cover as the mag. impulse clicks. If real close your good. A bit after is better than ahead as that might kick back some.
 
Hey John T - Why am I messing with green stuff? Kinda stumbled into it. Was early evening and I was the only other person around when the owner gave up trying to restart his old A. So I offered my assistance and succeeded, to the great delight of us both(!)

Disappointed you could not make it to the NY JD Expo XIII in Canadaigua. It was a good show, but VERY muddy this year. Hope we can meet again at another show someday, green or otherwise!

...Bob M
 
Thanks to all who responded!

Since the tractor starts/runs fine I'm gonna leave it alone. And I'll let the NEXT poor soul who gets to fool with the old tractor figure out the mag's 180 deg out and the plug wires are reversed(!)
 

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