Re: Quick question on the GM HEI dist on 258
OK, here is the rub bub...
You will need to look closely at the new gear.
Look for a 'Dimple' (looks like someone started to drill into the gear, then stopped).
Not all AMC gears have this Dimple, so you may not find one...
If you find one, It will be about 25 degrees from the roll pin hole.
Install the rotor on the distributor correctly.
Install the gear so the 'Dimple' and the rotor nose face the same direction.
If you don't have a 'Dimple' the only other way to do the install correctly is to cut a pretty large hole in the side of the distributor cap around the #1 spark plug wire tower, paint the nose of the rotor white so you can see it with a timing light, and start the engine.
As you rev up the engine and the vacuum advance and centrifugal advance come in and out, notice if the rotor nose 'Sweeps' from one side of the #1 terminal (retard) to the other side of the terminal (advanced).
If the rotor starts right on the terminal, or already past the terminal, and proceeds to get further away from the terminal, you need to take the gear off and try again.
This is called 'Rotor Phasing' and it is critical to a correctly functioning engine ignition.
When a GM HEI cap fills up with Ozone (Ionized Air) and gets a little carbon dust built up, that rotor placement during ignition coil discharge will fire the next cylinder 90 degrees too soon.
GM HEI caps don't have venting of any kind, so Ozone build up is a real problem.
It can (and will) fire more than one plug at a time if the rotor phasing isn't correct and the Ozone builds up.
Firing the next plug in the order is called "Cross Fire" and firing more than one plug is called "Multiple Fire"
Multiple fire and Cross fire both show up as Detonation, and both are VERY hard on the engine.
The Ozone building up can also induce Ground Fire.
Ground fire will show up as a dead miss.
When the rotor nose gets too far from either terminal, and conditions are right with Ozone buildup, the spark energy will fire to the metal components inside the distributor.
That's called 'Ground' Fire.
If you want to see if your distributor is Ground firing, look for 'Red Dust' under the rotor and on top of the advance head and weights.
If you find 'Red Dust', you are holding proof that your distributor is Ground Firing, and the rotor has been compromised.
There is a way to side step the problem of the ignition coil in the distributor cap.
If you use the distributor cap (or entire distributor for that matter) from a '76 Chevy pickup with 250 CID I-6 you will find that it uses a remote coil and coil wire.
The coil from any GM 4 cylinder with HEI will work, as will the coil connector.
This takes a huge magnetic field away from the top of the distributor, and the effects to the module and wiring through induction are nullified.
You also loose the liability of the unsealed coil in the cap.
Greatly reduced lightning strikes to the module, distributor housing, and your hands if you are unlucky enough to be in the area...
GM HEI coils in the caps leak high voltage like crazy!
I've seen the voltage come from under the coil cover, snake over the outside of the distributor cap, and ground to the distributor housing and vacuum advance!
I've seen high voltage leak inside the cap from around the center electrode and strike the module directly!
Moving the coil is the single easiest, and best upgrade for the GM HEI.