help with mag diagnosis

BruceS

Member
My h was running perfectly with mag. Mag was set just right, firing on tdc. Mag abruptly lost spark. Replaced coil, condenser, points, rotor, cap. After going repeately by the book, I cannot get it to trip on tdc, which is the first mark on front pulley next to another one very close to it. I noticed that when you wind up the spring by hand, there is very little movement when you release it.
Could this be the reason why it won't trip in time?? Any thoughts welcome.
 
I guess I need more information. You can't change the timing by merely taking the mag off. You could have it 180° off but then it would simply fire on the wrong cylinder. It would still be @ TDC on the mark. UNLESS you pulled the drive gear out with the housing. You surely didn't do that did you? And I am not sure what you mean by "you wind up the spring by hand, there is very little movement when you release it" If you keep turning clockwise it gets tighter, then trips and releases itself. Right?
 
(quoted from post at 09:13:08 05/29/15) My h was running perfectly with mag. Mag was set just right, firing on tdc. Mag abruptly lost spark. Replaced coil, condenser, points, rotor, cap. After going repeately by the book, I cannot get it to trip on tdc, which is the first mark on front pulley next to another one very close to it. I noticed that when you wind up the spring by hand, there is very little movement when you release it.
Could this be the reason why it won't trip in time?? Any thoughts welcome.

Sounds like you should take the impulse mechanism off and look it over. Sometimes they are so gummed up with gunk that has accumulated over the years that they don't work properly or you could have a broken spring.
 
When you replaced the points, did you get the cover back on exactly how it came off? There are a set of gears in it that drive the rotor and it is easy to put it back together wrong, which will have the rotor pointing somewhere other than the #1 distributor post when the impulse trips.

I check them by taking out all the spark plugs, putting my thumb over the #1 spark plug hole and turning the engine over slowly by hand. When the pressure of the compression stroke pushes my thumb off the hole, shine a flashlight in and get the piston to top dead center. Then check the rotor. If it isn't pointing at the post for #1, it is out of time. Take the points cover back off and realign the gears so the rotor is pointed the right way for #1 at TDC.
 
That's the problem. Mag trips past tdc when you look at the pointer. RE: tripping mag by hand, it trips ok, but spring gives very little resistance right before you turn it hard to trip it. Hope this explanation helps.
 
If you have done exactly what you said, on an H4 mag, you must remove the rotor drive cover to get to the points. If so, did you time the rotor drive gear correctly to tha armature gear? If not, that would be you issue.

If the impulse spring had broken, that would not have caused the mag to lose spark. So, if you replaced what you posted, the only way that the rotor would be out of time is if the rotor drive gear is not timed properly.

There are 2 marks on it, L and R. Since this is not a diesel or W9, use the R mark for the timing.
 
Did you dip the drive end in some kerosene or something to clean it sometimes it will sure make the spring and the other parts work much better get a better trip and spring action. Owners manual recomends it once a yr.
 
No, I don't know what you mean by "very little movement". It will only spring forward a quarter turn at a time. I'm as confused as everybody else. Yes, you could have gotten the internal magneto gears out of time but that won't change when the impulse trips. That would only cause the rotor to deliver the spark to the wrong place.
 
howard, I agree that the internal timing won't change when the impluse trips, but it will change where the rotor is when it trips................ :)
 
yes, I know that Tom. But the original posts only say he was having trouble with the
impulse tripping at the right time. Lets fix one problem at a time. You can change the
points without messing up the gears. Either cuz he knows better or by chance he could have
left the little cover on. If he didn't we will find out soon enough.
 

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