Off-Road Forums & Discussion Groups

Off-Road Forums & Discussion Groups (
-   Jeep-Short Wheelbase (
-   -   Quick question on the GM HEI dist on 258 (

shawnscj 04-15-2002 06:44 PM

Quick question on the GM HEI dist on 258
OK, I got hte distributor, I have the relay, and I just got my drive gear in today from 4WDH. The bottom of this gear look very long compared to the one I pulled off the distributor, is it going to interfere with the oil pump? And one more question, I didn't pay very close attention to the gear before pulling it off, it looks like if it goes on in the wrong manner (180 off) it might be off by 1/2 a tooth, but this shouldn't make too big a difference, I am sure I can just adjust the distributor to get the #1TDC and the distributor lined up with #1.

35inchcj 04-15-2002 07:59 PM

Re: Quick question on the GM HEI dist on 258
the AMCv8 drive gear is a mirror image of the 258 drive gear, make sure that the height of the gear doesn't go any deeper than the factory one, use the roll pin hole as a reference. you will actually feel the gear engage on the cam as you drop it in. do you want to perk it up a little more? add the MSD super HEI kit, its a new module and coil, along with a spiral core wires, this with a few other carefully selected mods have removed the wow I could have had a V8 feeling

Junk Yard Genius 04-15-2002 10:16 PM

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.

Ulfinator 04-16-2002 02:54 AM

Re: Quick question on the GM HEI dist on 258
Well that is very interesting to know...Seeing as I am know almost nothing about ignition systems I have one question about it...Will the same thing you descibed above work on the HEI distrib in on the 4.3L V6 in my Jeep???...

shawnscj 04-16-2002 06:33 AM

Re: Quick question on the GM HEI dist on 258
Thank you TeamRush
As always, I just recieved way more information than I expected. Thanks, and It has the dimple. It all makes sense.

Junk Yard Genius 04-16-2002 01:42 PM

Re: Quick question on the GM HEI dist on 258
Rotor phasing will work on all distributors that have a centrifugal advance, and most that have vacuum advance.

If the advance is controlled by your computer, the only way to phase the rotor is to move the reluctor around the shaft.
Or in the case of a GM HEI with the three screw top ring on the mag trigger, you can move the mag trigger points by simply rotating the outside ring one screw hole...
That sould be the equivlent of about 24 degrees of rotor movement... if I remember correctly

Ulfinator 04-17-2002 12:11 PM

Re: Quick question on the GM HEI dist on 258
Interesting how I posted my message chronologically after yours TeamRush but it ended up higher in the flat view. TeamRush could you do me a favor and just look at my short reply above and give me a quick answer. Thanks...

Junk Yard Genius 04-17-2002 01:44 PM

Re: Quick question on the GM HEI dist on 258
Is the 4.3 V-6 for the even fire, or the odd fire?
I can't keep the V-6 family straight....

If it's an odd fire, you will need to move the Reluctor inside the pickup coil, or the Pickup coil around the outside of the reluctor to change rotor phasing.

See if you have the three screw top ring on your pickup coil...

If you want to pursue this, start a new thread with a title like, "Ignition, 4.3 V-6 Questions..." or something similar and I'll try to help.

All times are GMT -5. The time now is 08:05 PM.

Powered by vBulletin® Copyright ©2000 - 2021, Jelsoft Enterprises Ltd.

User Alert System provided by Advanced User Tagging (Pro) - vBulletin Mods & Addons Copyright © 2021 DragonByte Technologies Ltd.
vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2021 DragonByte Technologies Ltd.
Copyright 1994-2009, VerticalScope Inc. // Off Road forums & discussion groups sitemap
side by side | atv | dirtbike | snowmobile | sandsport | competition | land use | Jeep | Toyota | Ford | GM

For the best viewing experience please update your browser to Google Chrome