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Discussion Starter #1
Hi Folks,
I pulled a C12 out of my fathers barn a few weeks ago and got it cleaned up and running. Really it didnt take much and runs like new. This is the second one out of the barn and is going to take a bit more I'm afraid. I put some fresh oil in it and put a battery on it. It turned over great and had good compression. I had no spark so opened up the box that the plug wire comes from. I cleaned the points and put it back together...still nothing. Is there something I should check first before ripping into it too deep? Thanks for the input.
 

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Gravelyyard.com
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One cause could be shorted kill button wire. To test for that, disconnect the small wire that runs from the handle bar to the magneto (the box with the park plug wire). Try cranking it to see if you get any spark. If you don't, it's probably a bad condenser and you'll need to replace it.
 

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Discussion Starter #3
Thanks, I pulled the wire and still nothing. Is there a specific condenser or should any mower shop have one. Also is there a way to test the output where the plug wire goes into the box? Just with a meter or something to be sure I don't have a bad plug or wire. Thanks again for the quick reply
 

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Does the magneto make a loud snapping noise when the engine is turned over?
 

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Take the magneto off and put it on the bench. It is much easier to work on that way. Take two bolt off and it almost falls off.
 

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Clean and set the points to .015", clean the wire connection in the cap, invest a few bucks in a new Autolite 3076 spark plug, insure you have a wire core spark plug wire. Aways have a shorting wire or grounded spark plug hooked up while cranking the magneto, generating spark with no place to go is very hard on the coil. New points and condensors can be found on ebay.

http://cgi.ebay.com/WICO-Points-Gravely-Tractors-NEW-/300542358744?pt=LH_DefaultDomain_0&hash=item45f9b874d8

http://cgi.ebay.com/WICO-Condenser-Gravely-Tractors-NEW-/300542359443?pt=LH_DefaultDomain_0&hash=item45f9b87793

Roger,
 

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To time the magneto, you can place a small diameter wooden dowel rod about six inches long or longer on top of the piston and 'watch' the piston travel. Mark the dowel at TDC of piston travel. You want to hear the impluse arm 'snap' at TDC on compression, if not adjust the drive coupling.

The drive cup on the back of a Wico has a timing mark on one of the two drive nubs, when that mark hits the two dots it will always snap, it is just the way the magneto works, unless someone has taken the magneto apart and put it back together wrong. The magneto is driven by the exhaust valve cam extention. The exhaust valve and magneto turn at 1/2 the engine or flywheel speed. The magneto fires once every four cycles.

"How do I know I am on the compression stroke?" You can feel the compression with a finger in the spark plug hole, or you can try blowing into the hole. The exhaust valve would be open on TDC of the exhaust stroke.

Magneto timing is adjusting the drive coupling so that the impluse fires at TDC on comression, and while making the adjustment rember to maintain .015" clearance between the drive block and coupling,

03.20.2011 009.jpg Magneto back 002.jpg

Some exhaust cam shafts even had a TDC mark on them,

Magneto mark 004.jpg

Roger,
 

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"Can you use a timing light on an old Gravely?"

Knowing that the magneto will always fire a timing light when the drive cup lines up with the bar, then we cannot flash the back of a magneto to check timing.

Something turning with the engine could be flashed in relationship to Gravelys spec of the piston being 5/16” BTDC, or 27-30° BTDC. Maybe you could figure out how to place a degree wheel on the timing pinion shaft.

I was going to try marking the exhaust valve shaft and front case with timing marks when the piston was exactly 5/16” BTDC. Now you should be able to flash those marks with the engine running and they should line up with each other. If they do not, then adjust the drive coupling. Just seemed like too much hoopla for so little when adjusting the impulse snap at TDC is so easy.

Roger,
 

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Hello Fella's,

I have hooked up a timing light to check my two walk behinds.
Initial timing was set to fire at TDC, and for the heck of it I hooked up the timing light and it flash's and shows the drive coupling lined up with the straight line when running.

Joe Kiba
 

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Joe,

The magneto fires the timing light and the magneto will always fire at the straight line on the back of the magneto while running, with the impluse arm out. It is just the way the magneto works. But how close does that flash of the timing light occur to the engine being 27-30 degrees BTDC on compression? What do you flash the timing light at to check that?

Roger,
 

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Hello Roger,

When I used the timing light on my two tractors, I aimed the light at the Magneto. The straight line mark on the body of the Magneto and a mark on the Drive lined up, the light showed they fluctuated a little bit, but I was curious and tried it.

But I have them timed to fire when at TDC. I just tried the timing light for the heck of it.

Joe Kiba
 
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