magneto on 29 D

[Coltond202]

I was told in the main forum to come over here and ask about my Splitdorf magneto on a 29 D. Our magneto is just like the one pictured only everything internal is new along along with cap. When the tractor is running I see a spark between the main cap and the cap over the points. When I take the main cap off there is a thick copper wire about a half inch long attached to the cap and it looks like this is were the spark comes from. I think that it is causing my plugs to cross fire and I get flames out of the intake, I dont like that. Can I cut off this wire, what does it do?

 

[Bob]

I'm NOT real familiar with that mag. HOWEVER, some mags have "coil protectors"... spark gaps on or near the cap that are gapped wider than the spark plugs, and give the spark a place to jump if a plug wire falls off, or whatever, to save the coil from the spark, which has no other place to go, from trying to "kill" the insulation on the coil and it's windings.

Could that be what you are seeing???

Do you have GOOD solid-copper core spark plug wires? (DO NOT use carbon reistance wires with old mags!)

 

[Coltond202]

No there good wires with sodered ends and everything

 

[Duane Larson]

Coltond202,
You likely have a Splitdorf 246T magneto, which is correct for your D. If you look closely at the pix, it shows only two spark plug terminals on the cap. Does your cap have two or four external terminals? All caps have 4 internal brushes since they are designed for 4 cylinder engines. If it has two external terminals, the bottom two brushes are connected to a spark gap in the lower quadrant of the distributor cap, which provides a short path to ground (on the point cover) for the brushes not being used. An ohmmeter will show the bottom two brushes are connected to the spark gap point.

If the cap has four plug terminals (for a 4 cylinder engine), the bottom two need to be grounded so the coil can dissipate the unused energy in a two cylinder application. If the grounding is not carefully done you can get all sorts of strange effects.

Post back with the number of spark plug external terminals on the cap. If you have a heavy wire somewhere inside the cap, something has been modified for some reason. However, some provision must be made to dissipate sparks not fed to plugs, or it will be hard on the coil.

 

[Coltond202]

It has the correct 2 plug cap like the one in this picture and the cap looks like someone just bought it and slapped it on with no adjustments. What would happen if I took the 2 bottom brushes out? If nothing else could I take them out and start it for a minute to see if I still get an external spark to see if that is the ground?

 

[Coltond202]

That was a stupid reply, I can check it with an ohm meter.

 

[Coltond202]

I am not to familiar with this magneto. The brass switch in the back should kick up when running correct? When the switch is down It has a good impulse snap but the impulse doesnt catch when it is up. As soon as it turns faster than I can spin the flywheel by hand it flips up.

 

[skip33652]

leave the brushes in!

 

[Duane Larson]

You are more likely to get an uncontrolled spark if you remove the brushes, since the spark energy has to go somewhere, and most likely you won't see it as it will ground somewhere internal in the magneto. With the brushes in place, the sparks go directly to ground.

These magnetos do not provide a spark on the exhaust stroke (those are the sparks that are grounded), only on the compression stroke. The owner's manual explains how to do the magneto timing with this magneto, and it must be done just right. It does not work to switch the wires at the magneto (like on a Wico C or X) if the timing is incorrect.

 

[Coltond202]

Its timed exactly to the books specs. I am just worried about seeing the external spark and I was hoping it could be a reason for getting flames out the intake when the valves are all good.

 

[Duane Larson]

The external spark you see is what PREVENTS you from getting a spark on the exhaust stroke. On a D, the intake opens at 1.5 deg BTDC, and the exhaust valve closes 11.5 deg ATDC, so there is 13 deg of valve overlap and the possibility exists of spitting fire if hot particles still exist in the exhaust stroke which ignite the incoming fuel. You don't see that on A, B, G because the intake valve opens after the exhaust valve is closed. That overlap is one reason the D magneto grounds the exhaust spark.

 

[Coltond202]

Thanks alot I was told you were the man to talk to.

 

[DRL]

Duane,
You might want to watch Coltond202's video of his tractor running to see what he is up against. Something ain't right.
Poke Here

 

[Coltond202]

forgot to put that up yea something aint rite. The valves look fine and I just adjusted them, and the cam is on time. Its a mystery.

 

[Duane Larson]

Well, something is not right! It appears the tractor is being turned over by the belt, and is not running on its own? If it showed up in my shop, I would first pull the spark plugs, lay them on the engine but away from the plug holes, and rotate the engine by hand to satisfy myself that each plug was getting a spark at the end of the compression stroke. It sure looks like a timing matter to me - either valve timing if the engine has been apart, or a magneto timing problem.

 

[Anonymous-0]

Looks like there's not a twist in the belt. Running backwards?

 

[Coltond202]

No we started it with the belt that video was taken when its running the belts still turning but the clutch is disingaged.

 

[Coltond202]

I will admit we are just college kids and I am the only one to ever work on 2 cylinder previously. However yes, the belt is spinning the right way, there is a twist.

 

[Duane Larson]

Coltond202,
Have you had the engine apart, such that there could be a problem with the crankshaft to camshaft timing? If not, I would recheck the magneto timing as follows:

Remove the plugs and lay them on the engine so the case is grounded, but away from the spark plug holes so any air/fuel mixture coming out the hole won't be ignited. Leave them connected to the magneto.

Rotate the flywheel, and have someone hold a thumb over the spark plug hole to determine when the piston is on the compression stroke - a distinct pressure will be felt. Rotate the flywheel so the piston is at TDC, at which time the LH Impulse mark on the flywheel should line up with a mark on the transmission case at about 3:00 o'clock, and the magneto drive slot should be close to horizontal.

Set the impulse trip lever on the magneto - this ensures the starting spark will occur at (or very near) TDC. A mechanical stop will engage part of the impulse unit when it is properly set, and prevent it from rotating.

Turn the engine over enough times that you figure out which plug fires during which part of the stroke. You will observe a "click-spark, click-spark, click-no spark, click-no spark" pattern, and make sure the plug wires from the magneto are such that the spark plug on the flywheel side (#1 plug) sparks 180 deg before the plug on the pulley side (#2 plug). The two "no-spark" clicks are when the spark is going to ground, as discussed earlier in this post.

When you are confident that you understand the pattern, rotate the flywheel until the #1 cylinder is on compression, and the #1 plug fires when the LH Impulse flywheel mark is lined up at 3:00. Then replace the plugs, and hook the wire which sparks first to #1, and the wire which sparks 180 deg later to #2. All during this process the impulse trip must be set so you hear a distinct "click" from the magneto at each spark. If you do not hear this click, the impulse spring is likely broken and the timing can wander within about 60 degrees. This could be your problem.

Making sure the impulse trip is set, try to start the tractor. As soon as it hits a lick or two, the engine speeds up to greater than 200 rpm, at which point centrifugal force causes the impulse trip to disengage, and the timing changes from TDC to about 35 deg BTDC.

Please post back after you try this process and let us know what is happening.

 

[Coltond202]

When I originally timed it the crank case cover was off and I made sure the TDC on #1 was in line with the left hand spark on flywheel. The magneto seems to be sparking rite at low RPMs.