If it ran perfectly for five times, then started doing this, it doesn't sound like a mag timing issue. In my limited magneto experience, more often then not it is a points issue. check your points, make sure they are really clean, make sure they are set to the proper gap, someone will be able to provide the proper point gap spec. also check the post that the acts like a hinge pin and allows the points to open and close. make sure that the points aren't hanging up. that was the issue with one of my ponys, it had good spark, but the spark was intermittent. the points weren't closing fast enough and would cause a late spark and a backfire out the exhaust.

if you roll the engine over by hand, you should here the magneto "clicking" when the impulse coupling snaps over. you can see this inaction if you remove the magneto cap. as you roll the engine over the rotor will stop turning even though you are still turning the crankshaft. when the impulse coupling trips, the rotor moves really fast and then starts moving at a normally speed again as you continue to roll the engine over.

another thing i found, is that some of the electric starters on d6 pony motors roll the pony over fast enough that the impulse coupling doesn't work (especially if you are using a 12 volt battery), this can cause a weaker spark but it should still have enough spark to fire the engine.

Sometimes the impulse coupling dogs may not be working correclty. if you remove the magneto, and are holding it in a different position then when it is mounted on the machine, i have found that the impulse coupler doesn't work. the little dogs are basically like a flywheight in a governor, at slow speed (rollingengine over by hand) the dogs stick out and catch until the spring loads up and the it trips the dogs allowing the spring to snap the magneto over quickly. as the engine speed increases, centrifugal force acting on the dog weights through a fulcrum pint cause the dogs to retract and the impulse couple becomes a straight coupling as the spring holds it in one place. i have not experienced an issue with the impulse couplings myself, but others have. it is possible that the dogs could be sticky.

Some one may be able to post up a better explanation and pictures or parts manual scan to help describe the impulse coupler action. or try a google or youtube search of impulse couplings.


Hope this helps.

The mag timing on those can only be "right" and 180* off. It is a simple process to swap the plug wires in the mag cap if you think it may be wrong. This is if the motor has not been disassembled and the gears reassembled incorrectly.

Or open the petcocks and find the approximate TDC of the compression stroke of the left cylinder and turn the mag so the rotor button points to the correct terminal on the cap before carefully aligning the drive coupling tangs with the mag drive gear notches and bolt it up. The correct terminal being either one really, just that you will know which it is.

Took it off check out video any advice would be appreciated thanks

Do not think the impulse coupling will work correctly with the mag in that upright position. Try the impulse with the mag turned like it was mounted on the pony. Check the nut holding the drive part of the impulse onto the shaft, looks loose. The shaft to drive connection is tapered and has a small woodruf key holding it together in the right way so that taper fit has to be tight so the parts do not selfdestruct.

Hi Steven,
as Stephan said the impulse works by gravity acting on the pawls/catches when the mag is upside down as installed on the engine. The looseness in the coupling is about normal as that is the spring loaded connection from the mag shaft to the drive coupling for the impulse energy spring to wind up on.
As long as the nut in the centre is tight it should be OK.
You may be able to reduce the clearance in the coupling, to eliminate some of the doubt, by removing the screw driver slot centre nut holding the coupling on and filing/grinding a few thousandth's off the inner end of the nut.

Always only ever turn the mag with BOTH lug wires fitted, or grounded with a small jump gap, or the one you are not testing grounded. You run the risk of a spark jumping across the internal coil windings and burning out the coil.

Only ever use copper or metal core plug leads on magneto's as the carbon wires have too much resistance for the mag to work properly--again it overloads the coil windings as does large jump gaps--no more than 1/8" when testing.

The correct points gap for these mags is 0.014" to 0.018" Yes you can experiment with the gap and maybe get a better spark due to it effectively changing the Edge Gap of the rotor. That is another internal adjustment that can be done on these and Eisemann mags. to set the mag to give Best Spark at low and high RPM's.

The following may help you with Edge Gap adjustment even though I was working an Eisemann. The Am Bosch mags have the same plate held by two screws in slotted holes--mark the starting point of the plate relative to the main housing and adjust the plate to give the best spark at the lowest RPM with about 1/16" jump gap. If you get confused you can then always reset to what you started with if the start point is marked.

www.acmoc.org/bb/showthread.php?23449-So...arting-Engine-Quirks

Hope this helps.
Cheers,
Eddie B.

Finally got the pony engine running after all this time so nice to have the pony back up on line. It ended up being the mag. 1 the impulse coupling was not functioning right. 2 the main screw that holds the points on was messed up so they were wiggling around and not opening properly I must have looked at it 100 times just did not notice it. Thanks for the imput guys got me guided to the prob. Now I can move on to other things plus I can start and use the cat 😄

Next on the list is to give the front idlers some care. Can I just weld them up to give the tracks a new wear surface or is that not the best route to go. I also have never had to split these kind of tracks. We use to have a d65e komotsu and it had zipper links on each track was pretty easy to take apart not sure on this style track is there a master pin? Thanks guys have a good one.

I have welded and built up rollers and idlers on my machines--just have to be careful to not overheat the seals

Look for a pin with a dimple in the end that will have to be driven out. There were some older types with plugs that had to be pulled to loosen the pin before it can be driven out. Haven't seen one of those in a while.

Finally got some time to work on the old girl figured it was time to fix the starting pinion. Boy was I in for a surprise when trying to start the cat the pinion will stay engaged as Long as the compression release is on but as soon as you take off the compression release it would kick out gets really frustrating trying to start it. So I pulled the poney I wanted to clean it up and fix some leaks on it anyways boy was I in for a surprise when I pulled the pinion. The case was broke in half between were the poney motor drive gear is and the starter gear for the diesel someone had brazed it back togeather but it didn't hold the latches are wore out the drive gear for the diesel has three teeth that are missing half the Tooth it goes on and on. At this point don't think it's worth trying to fix this pinion might need to just hunt down a new one. Took pics of the pinion but for some reason they come up blurry on here will post pics as soon as I figure it out why. Hope all is well for everyone