H.E.I. for 258. - Page 2 - Off-Road Forums & Discussion Groups
Jeep-Short Wheelbase All discussion of short wheelbase Jeeps: CJ, TJ, YJ and JK

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post #11 of (permalink) Old 05-28-2002, 01:18 PM
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Re: H.E.I. for 258.

I have a question about rotor phasing. Is this to position the rotor at the center of the terminal when the trigger tells the module it's time to fire?
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post #12 of (permalink) Old 05-29-2002, 12:32 PM
 
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Re: H.E.I. for 258.

**I have a question about rotor phasing. Is this to position the rotor at the center of the terminal when the trigger tells the module it's time to fire?**

It's not that simple...
When your distributor works, there is advance and retard happening all the time, so the rotor nose will move in relationship the spark plug wire tower on the cap.

If the rotor is already behind the tower, and you retard the system, that rotor will fire the cylinder behind the one in compression stroke.
That means you just fired a cylinder in the middle of the exhaust stroke, and wasted the cylinder that was on compression.

But that lost cylinder (or cylinders) isn't the worst part of rotor phasing gone bad...

If your rotor is already in front of the plug tower, and you advance the timing, you will fire the next cylinder in the firing order...
You loose power because the cylinder on compression stroke didn't fire,
BUT...
The distributor fired a cylinder at least 90 Degrees too soon!
You have no idea how hard that is on the engine!
The cylinder fires too soon, and the force of the burn is trying to send the piston down, back the way it came!
You can easily pound the bearing out, pound a hole in the top of the piston, break rods and rod bolts, and worse...

<hr>

The idea is to get the rotor to start on the back side of the terminal and then sweep past the terminal as the advance comes in.
This way the rotor nose is always VERY close to the proper terminal.
<hr>

The older Delco Breaker points distributors have been made real easy by MSD.
MSD has a cap and rotor that will adjust so easy it's scary!

There is no way to adjust the rotor phasing on the Prestolite distributors...
The only way I can think of is to machine a new shaft every time you want to adjust the rotor phasing...

GM HEI distributors are virtually impossible to change rotor phasing. It can be done, but it involves a head mill and a TIG welder...

The Motorcraft distributor is very easy to change the phasing.
The cap design lends it's self well to making a test cap also.
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