The condensor is wired in parallel to the primary ignition circuit as close to the contact points as possible. The series resistance of the condensor allows current to flow thru the closed contact points so that the magnetic field inside the ignition coil may build up. The contact points must make and break this circuit without arcing! The primary current wants to continue to flow jumping the contacts as they begin to open.
The condensor provides another route for this current to travel thru the series resistance and storage capacity as the contact gap gets wider. ( Now too wide to jump)
The correct capacity will store this energy until the contacts close allowing the current to again flow directly to ground dumping the stored energy. A incorrect capacity for the system will allow the contacts to arc and incorrectly turn the primary on and off.
The pictures to the right show the effect on a running system. On the top pic the engine is only firing on 5 cylinders. Even this can be random due to rpm , heat and actual defect of the condensor.
The lower pic shows the same distributor with a proper new condensor installed...
A condensor must have three major properities, shown here on a automotive Sun tester:
1-Leakage-a designed leakage to ground. Cant be a short and is controlled.
2-Series Resistance- resistance ( high) to current flow. Cant be open or shorted.
3-Capacity- storage capacity measured in micro farads or MFDs
CONDENSOR STORY OF THE DAY......FEB 24TH 2016
1951 LINCOLN 337 FLATHEAD...Customer had rebuilt carb and taken it apart two or three times . Engine would start and run then switch over and loose a few cylinders and then die.
Thinking it was still the carb wanted to know if i could find someone to build carb. I asked him to bring the distributor to me. Visual inspection shows the very cheapest parts available. Put on tester and it would run and then loose cylinders and then cut off. At the same time the contact point shows huge arc! Added new test condensor and bang it was fixed and hitting on all eight with no arc. Condensor tester shows no capicity, cut away shows poor connection inside!!!!!!!!
The techology exists today to create a perfect automotive condensor , how ever most aftermarket condensors dont live up to the rigors of the flathead engine.. I just bought 24 brand name condensors and when tested only three was good!!! When returned and discussed with my area counter man , he stated who cares ? You are the only person in Indianapolis that ever buys these and we dont sell hardly any these days.
My fix for that is we buy a vertex magneto condensor from a friend thats in the racing business . He has 10,000 made up of very high quality at a time and demands perfection !!!!!! Perfection costs money they sell for $32 ea. and must be special mounted on the early Fords..
These work very well and i have never seen a defective one ! However you must make the mounting bracket work in each application.
Shown below is a few pics of how this is done . I take a factory mount and old condensor, remove ( with a small torch) the factory bracket holding it to the distributor and solder it to the new condensor (allowing for clearance) and use a small 8/32 bolt for connection to coil.
Works like a top and looks pretty close to the orginal unit. This isnt the only way to do this but to me its the easiest.
Shown on our " complete polished helmet unit with small contacts, two bolt ignition coil and 11A advance parts " This would be the ultimate helmet distributor!!
N.O.S. ????? I talk to customers quite a bit and hear the word N.O.S. ( new old stock) Even though Ford made some great parts odds are its no longer any good after 73 years !!! Condensors are made up with mica and foil , vacuum packed and sealed! Normal changes in temperature (ie:hot/cold ) could make them defective
After many years they dry up and often fail just laying around. Buy new when possible!!.
Actual Customers distributor!