In addition to working and learning about setting the gaps on a t mag, Iím messing with a Bosch Du4 magneto. From what Iíve read from previous posts, the point gap should be around .020 or so with spark plug gap at around .025.
This is a dual magneto, converted to a single. Otherwise it has two points. The secondary has been disconnected from a single coil.
It has been a hard to start car, last thing that I havenít messed with is the magneto points.
Any input or thoughts?
My understanding is; the DU4 dual was so you could start the car on battery/coil and then switch to mag for running on cars without an impulse cuppler.
What you mean by converted?
The only thing you would be doing(?) is not connecting the lead to the coil/battery.
RE; "Otherwise it has two points" Do you mean it has two sets of points(?) or just referring to you are not using the battery/coil lead tower?
You could get DU4's for different directions of rotation, do you have one, or has yours been converted for correct rotation?
.018-.020 sounds about right.
Do you have an impulse cuppler? if not could be why car is hard to start.
Robert as long as the mag is good it should start however you have to advance the mag at least a 3rd of the way in order to get spark at hand cranking speeds.Every car/ engine is different so you will have to play with the amount of advance.Then when you have that figured out how to start cold , you get to play again when the engine is hot.The reason you must advance the mag is to have the points open when the armature is in a position in reference to the horseshoe magnets that allows the greatest collapse of the magnet field to be induced into the armature to give the hottest spark at very low hand crank speeds..Hence the reason for the dual type mag on battery lots of spark at hand crank speed.
Hope this helps. Cheers
I had to close up the spark plug gap to get my '13 Speedster with DU4 to hand crank. The new owner installed an impulse which made it much easier to start. I never had issues with the point gap. There may be a post from back in 2009 when I was setting mine up for the first time.
Any mag will be switching the armature from north-south to south-north magnets when it produces the hottest spark. You can feel this by turning the mag over by hand and feeling a high resistance to turning at that point. The points should be opening at the same time as the armature is switching magnet polarity. The gap should be set to provide this condition.
Over time the magnet in a mag will loose strength just like in the Ford magneto. This will cause the spark to be weak. If this is the case you will have to re-magnetize the magnet.
The points should also be clean just like in a distributor and no loose connections.
I believe Mark is right about how the mag was set up to start on battery. There was an article about this in the HCCA magazine a few months ago.
Update on progress. Iíve balanced the cam shoes, set points close to .016 - .022. Cam shoes are long, taking up 90 degrees each.
Started, sputtered, and died.
Iím going thru another magneto, with a strong spark. Cam shoes are short at about 30 degrees of the arc. Iíll install tomorrow to find if it makes a difference.
I would like this 11 Buick to be as reliable as my 16 T.