Hi,

i´m new here and found this forum when browsing for help with a non-sparking magneto. I live in sweden and there are a lot fewer people to ask about old cat´s overhere.
I have a cat d4 that runs great if you pull it to start with a wheelloader but the pony engine doesn´t work. The problem is the magneto who don´t give any sparks. I have tried it on the workbench with a drilling machine and i get spark´s at 2000 rpm but not below. I have measured the resitance i the coil and it´s about 7,2 kohm. What could be wrong?

/gustaf

What is the model number of your magneto??
For the American Bosch Units coil resistance should be about 6.2 kohms and generate a 9 MM spark at 200 rpm. Lots of things to check but weak magnets would be a likely candidate. I can post the trouble shooting guide with your model number.

You might check all the connections to points, capacitor, points to baseplate, kill terminal insulators, wire and switch to make sure that a high resistance connection is not weakening the spark or a leaky insulator isn't keeping voltage down. Have you tried a new capacitor?

Also it is possible baking the mag to dry it out might help. I would say keep temperatures in the < 100* C range for safety while baking.

My 7u with the bosch mag did just the opposite. It had good spark untill
the engine warmed up , then it lost all spark. I changed the coil on a chance
and hav'nt had a problem since. I figure the coil was breaking down once it warmed.

I sure aint no expert on any thing but I just got my neighbors pony moter running again after he gave up on it 15 years ago because of mag trouble. I converet it to battery and automotive coil inginition. I disconneted the mag coil wire and used the mag points and a two lead out coil off a two cylinder onan moter. Two automotive coil can be use[one for each spark plug]. His pony moter fires up at the touch of the starter button now and he is very pleased with it.

Richard

Before you do anything radical, try spinning the magneto over in the dark and see if there are any sparks leaking from the coil to any housings, this could be the reason for it not sparking untill such high revs, only problem is the room needs to be completly dark!! if coil leaks spark mark the point it comes from and you can simply glue the area with epoxy resin and it should fix the problem. Cheap and worth a try.

thank´s for all the answers, i´ll try them when i get time. The serial number for the magneto is MJK 4/236OD47, and i also have one with number MJK 4/236OD47 . The only diffrens i can spot between these is the screw where you attach the wire to the kill-switch. The most strange thing is that it´s the same problem with both.

/gurra

Both those numbers are the same. I suspect one is a C47 model. They both are correct for the D4 application. Here is the service information which should pretty much cover your magneto problems. I also have parts breakdown if you should need parts numbers. Does anyone service magnetos in your location in Sweden??

Also be sure that you are using solid core wire spark plug wires and non-resister type spark plugs.

once again many thanks for your quick answers, i´ll get back when i have tried these tips. (I´ve been in contact with one repairshop here in sweden but the pricing for renovation made want to try myself first.)

/gustaf

Hi again,

I have now changed condenser, sparkplug-wires and sparkplugs. I now get sparks below 1000 rpm on the workbench, but does anybody know at how low rpm the magneto should make sparks with sparkplug? I use NGK B6S sparkplugs, are they right and what should the gap be in mm?

/gurra