The Ford Barn

rotorwrench · 06-02-2022, 10:39 AM

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Does the magneto rotate on its drive axis for advance control? Or in other words, what does the spark control manipulate to retard the spark? Is the mag drive splined, geared, or have an adjustable coupling for timing to the engine? There should be a way to get the distributor rotor timed to the terminal that leads the high tension voltage to the #1 plug when the #1 piston is in firing position. The rest is just making sure the other high tension leads are set up for the proper firing order of the engine. In full retard, the mag should make its spark at TDC or within several degrees after TDC for best starting. Advancing the spark further will be done after the engine starts and is running well.

This would be one of the first application that I've ever heard of that actually has a driver adjustable spark control. Most mags are used for racing so they are set for full advance at all out speed. For starting, which can be difficult on this type of set up, the engine starter is engaged for a bit before turning the magneto switch on. A starting aid is always recommended to prevent kick back and allow for easier starting. The distributor portion of a magneto has to be rock solid with the internal timing of the magneto rotor & breaker points. If the distributor is independently adjustable from the magneto rotor then the internal timing would be off.

Some of the very large radial engines used during WWII and for some time after, had the magnetos separate from the distributors. The magneto would generate the high tension sparks which would then be sent to the distributors by means of two shielded and insulated high tension leads. The high tension voltage was then distributed to each cylinder in proper time. Timing for all this was critical for the engines to run properly. The Pratt & Whitney R4360 radial engine had 28 cylinders that had to fire off of those mags. They had Bendix "shower of sparks" starting aids to retard the spark and get those monsters to start.

After looking at several front plate Bosch magnetos It appears that these units have a rotating coil instead of a rotating magnet. Lucas used these type magnetos on motorcycles but they are a different design. With the rotating coil set up, the points plate can be moved a limited number of degrees before it becomes ineffective but it does allow for some spark timing adjustment. The model T has limitations on how much advance is effective anyway so I can see how it would work.

This info on the DU4 may help you. http://brightsparkmagnetos.com/libra...%20Magneto.pdf

06-02-2022, 10:39 AM	#6
rotorwrench Senior Member Join Date: Jun 2010 Location: San Antonio, Texas Posts: 17,410	Re: Timing issues, Bosch magneto/ laurel cylinder head Sponsored Links (Register now to hide all advertisements) Does the magneto rotate on its drive axis for advance control? Or in other words, what does the spark control manipulate to retard the spark? Is the mag drive splined, geared, or have an adjustable coupling for timing to the engine? There should be a way to get the distributor rotor timed to the terminal that leads the high tension voltage to the #1 plug when the #1 piston is in firing position. The rest is just making sure the other high tension leads are set up for the proper firing order of the engine. In full retard, the mag should make its spark at TDC or within several degrees after TDC for best starting. Advancing the spark further will be done after the engine starts and is running well. This would be one of the first application that I've ever heard of that actually has a driver adjustable spark control. Most mags are used for racing so they are set for full advance at all out speed. For starting, which can be difficult on this type of set up, the engine starter is engaged for a bit before turning the magneto switch on. A starting aid is always recommended to prevent kick back and allow for easier starting. The distributor portion of a magneto has to be rock solid with the internal timing of the magneto rotor & breaker points. If the distributor is independently adjustable from the magneto rotor then the internal timing would be off. Some of the very large radial engines used during WWII and for some time after, had the magnetos separate from the distributors. The magneto would generate the high tension sparks which would then be sent to the distributors by means of two shielded and insulated high tension leads. The high tension voltage was then distributed to each cylinder in proper time. Timing for all this was critical for the engines to run properly. The Pratt & Whitney R4360 radial engine had 28 cylinders that had to fire off of those mags. They had Bendix "shower of sparks" starting aids to retard the spark and get those monsters to start. After looking at several front plate Bosch magnetos It appears that these units have a rotating coil instead of a rotating magnet. Lucas used these type magnetos on motorcycles but they are a different design. With the rotating coil set up, the points plate can be moved a limited number of degrees before it becomes ineffective but it does allow for some spark timing adjustment. The model T has limitations on how much advance is effective anyway so I can see how it would work. This info on the DU4 may help you. http://brightsparkmagnetos.com/libra...%20Magneto.pdf Last edited by rotorwrench; 06-02-2022 at 11:23 AM.