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Is this right? (Cat D4 7U with Bosch magneto with video)

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2 months 4 weeks ago - 2 months 4 weeks ago #251151 by cantmetal
Good afternoon all,

A friend of mine and I are still trying to rescue a D4 7U - the first challenge was the starter pinion clutch as it was all seized up. I rebuilt it, and now it's working great.  Re-Installed the pony motor and discovered no spark.  I pulled the magneto and after removing the dirt and grime, I wasn't getting any spark from the points.  (I'm told if the mag is working, you should see a spark at the points).  After quite a bit filling and cleaning, I'm now getting spark - for the most part - from the points of the mag.  Please see the following video - does this look right?

youtube.com/shorts/VT09x8XAAN4?feature=share

1951 D4-7U
Last edit: 2 months 4 weeks ago by cantmetal.

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2 months 4 weeks ago #251157 by Old Magnet
That's a lot of sparking. I'd suspect a failing condenser which is supposed to limit that arching.

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2 months 4 weeks ago - 2 months 4 weeks ago #251161 by trainzkid88
the things that can give you problems are the kill switch as its a grounding switch and is normally closed in the off position. if it or the insulation on the wires is bad it will stop the spark.
bad plug wires will stop the spark these need to be the proper wire plug leads with metal ends not the silicone suppression as used today.

the spark plugs and there mating faces need to spotless so does the mating faces between the mag body and the engine. any dirt/grease etc can interfere with a good spark. magnetos rely on the return path between the mag spark plug and the block to work. even modern cars still rely on that path its just a bit more complex
a poor condenser will also affect the spark. often fit new condenser and points and a mag will work again and work just fine.the generic bosch condensers work just fine.

if it has good spark at the plugs but wont fire fit new plugs if it still wont fire try swapping the leads. i learned that with our d4 after fitting new leads it was opposite to what i thought.
Last edit: 2 months 4 weeks ago by trainzkid88.

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2 months 4 weeks ago #251162 by trainzkid88
the spark should be nice n fat n blue and thats not. yes i agree with OM change the condenser and see what happens.

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2 months 3 weeks ago #251170 by cantmetal
Thank you, condenser has been orders along with new points (just in case, will keep them as spares if nothing else). Order should be here late this week.

1951 D4-7U

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