Testing TI distributor parts

[G B.]

I've got a pile of old used Corvette transister ignition distributor parts from the sixties. I sure would appreciate some advice on how to test the stationary magnets (pole pieces) to determine if they are any good.

I've used an ohm meter to test the resistance across the two wiring terminals on five stationary pole pieces. These test readings varied from a low of .566 to a high of .848. Most were in the .566 to .603 range. Is this the best way to test them when off a vehicle? How can these readings be interpreted as a predictor of performance when installed?

Thanks for any help you can give me on this.

[Duke W.]

Re: Testing TI distributor parts

Jerry - the only tests of the pickup coil are static resistance and ground isolation. I expect the values you gave are K-ohms - you didn't specify. I don't have a spec for the TI coils, but it should be in any applicable year shop manual.

The static resistance value for the HEI pickup coil is 500-700 ohms, and I expect the TI pickup coil is the same or nearly the same. When mounted in the distibutor it should also be checked for insolation to ground - one test probe on either of the two leads and one to ground. Resistance should be infinite.

As long as the pickup coil resistance is within the specified range, and it is isolated from ground when fastened to the distributor, the ignition system performance should be nominal.

I never has a TI pickup coil fail in the time I had a TI on my SWC (the amp failed twice), but the pickup coil on my Cosworth Vega's HEI failed once. One of the leads broke right where it exits the windings due to vibration and/or action of the vacuum advance, which is constantly rotating the baseplate/pickup coil. Also, the Cosworth Vega inline four produces a second order vertical unbalanced shaking force that peaks at 13g/233 Hz at 7000 revs, and that's really tough on the pickup coil.

The V8 vibration environment is relatively benign because there are no unbalanced shaking forces or rocking couples below forth order.

Duke

[William C.]

Re: Testing TI distributor parts

Do a eyeball inspection of the distributor pickup coil for any cracks also. They will play H--- with the timing if present.