My 1913 Metz has a Bosch DU4 Model 2 magneto. This magneto has no "on-the-fly" spark advance lever, but I'm wondering if there is a way to adjust the timing other than changing the drive-gear position.
Phil
First off.......is it an impulse magneto and how is it driven?
It is gear-driven off the camshaft gear. Not sure about your "impulse" question, but it's a standard high-tension magneto. Here is a photo of two Bosch DU4 magnetos. The "Model 2" on the left is the one I'm installing, and is original to my car.
Phil
When you get it timed right make sure you know what the spark plug gap should be. It is usually less than with a coil ignition. Lots of mags get burned out from too wide a spark plug gap. One source says 15 to 20 thousandths for magneto ignition verses 25 to 30 for coil ignition.
Rich
Phil,
My 1911 Hupmobile uses the same DU4 magneto as your Metz. No, there is no way to adjust the timing other than to change the mesh of the gears. It is a fixed timing device. Also, to Craig, no it is also not an impulse magneto. One timing position. Seems pretty primitive to me even for that time frame. I would think that if it were timed so that you could crank start without kickback then the timing would be very retarded for running. That's how the Hupmobile is set up though and it seems to work OK.
Yes, I couldn't find any way to move the cams or the points ("interruptors", as they called them then). As far as I can tell, it is set to fire close to TDC. It'll be a while before I can actually run the engine, but I'll be very careful cranking it!
Phil
Many motor vehicles came with non-impulse magnetos as did a few tractors.
You need to "flip" the engine over the top to avoid getting a crank in your wrist.......or elsewhere......and I hate them.
An impulse "winds up" and trips off shortly after TDC and when the engine starts the dogs don't engage and you get anywhere from 20-40º automatic advance, depending on the magneto but, typically, 30º.
You have zero control over the timing with the magneto at the left.
Original or not I'd use the other one which gives you some control.
Could there possibly be some way to mount the magneto in such a way as to allow the entire body of the mag to rotate a few degrees with and against the direction of rotation? In other words, similar to the way the distributor body would rotate on the old "stovebolt 6 cylinder C#@&%lets for spark advance instead of spark advance by means of rotating the plate that the points were mounted on.
Howdy Phil and Steve,
Yep, the DU 4 on my '11 Hupp looked like the photo on the left too until I had the restorer add the manual advance like the photo on the right. That said, Steve is correct in stating an original Hupp Model 20 is a fixed timing device. I hope to set up some kind of bell crank device to advance and retard the spark from the cranking to operational aspects.