GM HEI distributor for an AMC V8
Most Jeeps with V8 engines have one of two distributor systems. A Ford Duraspark system or a Motorcraft points system.
The points system is relatively reliable and very simple. It requires periodic adjustment and maintenance using special tools. The Ford Duraspark system is all electronic. The distributor contains a magnetic trigger that sends signal to the controller and spark is distributed to the spark plugs from the coil. The Ford system is fairly reliable but failure is usually instant with no warning and no recovery except with replacement of the controller module. I was always a good idea to take a new replacement module along on the trail because these things always fail at the wrong time.
The GM HEI system was used in GM vehicles for approximately 20 years. It is a simple design using a magnetic trigger, electronic controller inside the cap, and a coil. A nice feature of the HEI is the coil is integrated right into the distributor cap, meaning no coil wire. This feature allows for a much hotter spark and increased gap on the spark plugs. There are many aftermarket high-performance coils available too.
There is a company called DUI that makes an HEI distributor for Jeeps, in this particular article we are using a custom made distributor we bought off eBay. It came complete with a new cap and coil. The old plug wires will not work with an HEI. You should buy a custom set of wires, we used a set of Live Wires from performancedistributors.com.
Installation is pretty straight forward. Disconnect the battery. Remove all the old Duraspark components (if equipped) Remove the plug wires making note of the firing order. Remove the distributor cap. Mark the old distributor’s rotor position so the new distributor can be installed in the same place. If you forget this step the engine will most likely not start or run real bad.
A down and dirty way to locate the start of a firing cycle is to remove the spark plug from the #1 cylinder and crank the engine in short bursts. Put your finger over the plug hole and feel for the compression stroke to force air out of the plug hole. Look down at the timing cover marking and line up the line on the harmonic balancer to the 0 line on the cover. BE CAREFUL – Watch out for the fan and make sure the Jeep is in neutral!
Remove the bolt and bracket that holds the distributor in and pull it out.
Install the new gasket onto the shaft and insert the distributor so that the rotor end is pointing in a direction to allow movement of the distributor to set proper timing. You may need to crank the engine 2 full turns to allow the distributor gear to engage the oil pump drive shaft located below the bottom of the distributor.
Once the distributor is fully seated lightly tighten the securing bracket so that you can properly set ignition timing after the engine is running.
Wiring up the HEI is easy. All that is required is 2 wires. One from a switched 12V circuit and the other from the Start side of the starter coil. This 2nd wire provides power to the distributor during engine cranking.
Install the cap and wires. Starting from the #1 cylinder and moving clockwise through the firing order.
AMC V8 Firing Order 1-8-4-3-6-5-7-2
The spark plug gap can be increased due to the hotter spark provided by the new distributor. Recommended gap is .050 – .055. This may be a good opportunity for some new spark plugs.
After all of the wires are installed check all connections and make sure everything is cleaned up and out of the way of moving parts. Attach a timing light so you can set the engine timing after it starts. Reconnect the battery and start the engine. If you timed the engine correctly it should fire right up. You will probably need to rotate the distributor to better set the timing before you use the light. When the engine runs smooth you should fine set the timing using the light. The recommended ignition timing is 8 degrees BTC with distributor vacuum advance disconnected and the engine at idle. The Jeep was set a bit higher about 10 degrees, high enough just before engine ping was heard.
If the engine doesn’t start or run correctly you may have the distributor of time. It is possible that the distributor will need to be removed and re-timed, refer to the above.
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