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

[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