Can anyone advise the quick / simple way to check if the magneto field ring has the correct continuity ????
- My thought was to use either a 6 or 12 volt battery, + at the contact point and - to the ring body..... is this right ?
The resistance of the Mag Ring is very low. Put a 6 or 12 volt light bulb in series with the mag ring. This will not, however, tell you if the chain on individual coils is prematurely shorted to the mag ring frame. To do this, you must disconnect the end of the chain of coils from the mag ring itself then check for continuity between the coils and the mag ring frame. There should be no continuity.
To check a field coil: Connect an ordinary 6V lantern battery to the mag (ground to the frame and positive to the contact button). Hold a hacksaw blade, small screwdriver, or similar steel bar over each pole face in turn. Each pole should have about the same magnetic pull on the blade. If, while moving around the coil, you come across a dead winding but all others before and beyond it have a good pull, that dead one is shorted out. If all windings beyond it are also dead, the last live one is grounded to the frame. If all seem OK, go around the field coil again with a small compass held near each winding in turn. The needle on the compass should do a 180 degree turn as it nears the next winding.
If this is an engine rebuild and you're thinking of re-using a typical original field coil, don't, even if it tests OK. They are full of old oil, making them hard to re-coat so that it will stick permanently. Even if the new coating does adhere OK, you're sealing in a lot of dirt and metallic sediment that will impair the mag's performance.
Using an original mag coil ring is like comparing using an original radiator or even older tires.
The insulation on the mag rings break down after years and years with grease and oil.
The radiators tubes slowly stop up and the copper even breaks down and gets brittle. The tires get so hard they start to crack. You have to remember these parts are close to 80+ years old. Age eventually takes its toll on these items.
I have used old and new mag rings, radiators and tires.
Its not a good thing when your driving down the road and the mag quits on an old original ring which you have used in a fresh rebuild and thinking of the work involved in taring the engine down again to replace it.
Been there and done that.
Thank you for that info, l have just come in from the garage and read your comments, but l am unsure what l have just achieved from running a multi meter over with the tone on, if l hold the + pos side to the contact point, and touch the - neg side to anything, l get a tone, copper, field ring body, magnet parts in the centre, that surely cant be right !!!!!
Yes that would be right using that method.
One lead is connected to the output post then that
coil is connected to the next one and so on for
all 16 coils.
The last coil is grounded to the body of the
support that holds the coils.
As stated above, you will need to unsolder that
lead from the frame that holds the coils to test
for short(s) in all the coils at once.
Or just do as stated and use the hacksaw blade
and 6V battery.
It is applying the same principal
as a growler test on a armature.
Thats a job for Monday morning.
cheers and thank you for the info.
RV Adnerson does a good job on rewinding field coils and they are priced very reasonable.