Bendix Coils Test Good, But Won’t Fire In Motor

[oldoutboardjim]

I have a customer who has two Bendix coils that he has tried in several mag plates, but they won’t work. When tested on a Merc-O-tronic, they spark fine. Ideas?

[ryanjames170]

has he switched out points between these difrent mag plates or has he used the same points.. if he has used the same points they might be shorted out.

or its engine side with the magnets.

[Doug Wilson]

are they not sparking or will motor not start. My ke7 mercury would not start due to crank shaft
seals leaking a lot kept thinking it was ignition issues but was not

Doug

how is it motors multiply when the garage lights get
turned off?

[garry-in-michigan]

Have you tested the capacitors ? . . . 😕

[Tom]

Is the Merc-o-tronic one with the stray voltage probe? Try ncreasing the gap and retesting, or checking near where the laminations come out using the probe.

T

[dave-bernard]

funny no one mentioned condensers.

[20mercman]

These Bendix Scintilla systems are often a very confounding system. I have actually had very good luck with the early style magneto’s found on the KE-7 and the KE-4, etc. The later oval style system with the black plastic cover are the ones that have been difficult for me. I have been told that Mercury had coils with a significantly higher number of secondary windings in the later systems. These were able to then produce a higher voltage with the available magnetic field created by the rotor. Often these will have the drop cylinder symptoms. I have talked to some pretty smart guys who worked for Mercury Marine who think that replacement coils may have been modeled after the coils with the fewer number of secondary windings. I have no way of knowing, but it may explain why these seem to run fine in the older style and not as reliable in the newer Bendix magneto. As for being able to make them work on the Hurricane blocks, a lot of these motors were built, and they ran successfully for a very long time. I have been working on these on some Mk-20’s and am still planning on working on it when time becomes available. I even picked up a KH-7 tower at Tomahawk that I intend to use as a test tower for Bendix Scintilla testing. The air gap between the rotor and the laminations should be about .008 and is important. Also wear or looseness between the magneto and the top of the cylinder can change the point gap. This will change the dwell of the charging of the primary windings and can also change the output of the coil. I have also talked to folks who recommend that the plug gap be reduced to about .018 – .020 range to reduce the required voltage. Others have mentioned the importance of clean and properly insulated contact points, and of course with any magneto, good capacitors are a must.

Steve

[The Boat House]

quote ddwilson:

are they not sparking or will motor not start. My ke7 mercury would not start due to crank shaft
seals leaking a lot kept thinking it was ignition issues but was not

That is the first question I would ask also.
Does the magneto produce a spark?

[jerry-ahrens]

That’s pretty interesting Steve, thanks for posting.The only other thing I could think of is an open secondary winding, but that’s probably far fetched, since the coil tests good on the Mercotronic. It might be worth checking this with an ohm meter, just to make sure. I’ve seen a couple old Johnson coils that had this happen.
I think I’d also do a surface leakage test too. Does this motor have the rubber boot that goes over the solder joint on the coil? The reason I ask, is that I have an Oliver motor (with bendix mag) that does not have the rubber covers to seal the secondary (spark plug wire) solder joint. When the motor is cranked, the spark will jump this open gap to ground, rather than firing the spark plug. The Oliver coils originally had the spark plug wire built in to the coil from the factory. It was just molded right into the coil. The new coils of course, require the wire to be attached or soldered . I need to get a couple of these rubber covers to fix this particular motor. If I remember right, mercs have some sort of rubber boot or cover here I think? Just a few things to consider…

[jw-in-dixie]

Early fifties I bought a used-one-time and returned to dealer as too feisty KG7. My good luck, altho the $150 I paid then is now = $3000 today. Used it on my 8′ runabout and shortly began to experience the Bendix dropping one cylinder syndrome. Replacement coils always got it going again. Still have it and it still runs.

A Bendix mag in good tune is about bullet-proof. Have had 3 go swimming and restart without pulling the flywheel. Not may mags will do that. Bendix ignitions were used on many airplane motors. Got to be dependable for that application. 😉

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