By: Terry L. Howe - 6/2002
|The 258 with the Prestolite distributor in my '75 J-10.|
|The Prestolite distributor with the distributor gear that was on the HEI distributor.|
|The big cap HEI distributor installed with 8mm wires.|
I have a Ford truck, but I seem to be a big fan of putting GM parts in my Jeeps. GM parts tend to be simple, reliable, inexpensive, and easy to find. These are all the features you want in a part that goes in your Jeep.
One swap I've always liked is the big cap HEI distributor swap in the Jeep 258 straight six engine. One of the great things about it is, it is extremely simple. When I replaced my CJ-6s tired 232 for a fresher 258, I put an HEI in the 258 rather than swap over the Motorcraft ignition the 258 came with. The HEI ignition has two wires that get connected to it, one is 12v which should be hot on run. The other wire is for the tachometer. It just doesn't get much easier than that!
The big cap HEI unit has a reputation for being very reliable. The Prestolite ignition was the first electronic ignition used on Jeep 258s and it does not have a great reputation. The Motorcraft ignition used on later 258s has a better reputation, but the computer controlled version seems to limit the top end you can get out of a 258. It is also convenient to carry an entire good HEI distributor and swap it in if you have a problem. Swapping the entire distributor is easier than trouble shooting coil, ignition module, and wiring if you have a spark problem on the trail.
GM parts are, on an average, far cheaper than Jeep parts. GM made a lot more vehicles than Jeep ever did and parts tend to be cheaper when they are massed produced. For example, if I wanted to replace the entire ignition for my '75 J-10 today it would cost $80.94 for the ignition module, $29.20 for the coil, and $72.33 for the distributor. The total would be $182.47. The same thing for an '81 C10 with a 250 I6 would be $169.91 for the all in one big cap HEI. Not a huge savings, but a saving just the same.
Used prices are of course a lot cheaper. I paid $15 for my big cap HEI distributor at my local u-pull-it. They charge $15 for any distributor, so I could of bought a Prestolite for $15, but I would not get the coil and ignition module in the deal. Lots of junk yards tend to charge a premium for Jeep parts because they are a bit harder to find which also drives up used prices.
Easy to Find
Many of the Chevy 250 straight sixes used in Chevy and GM trucks and the Chevy Nova come with the big cap HEI distributor. The distributor was used from '76-'82, but some early vehicles came with a different distributor with a remote coil. I went to my local Pull-and-Save and found one in an '81 1/2 GM pickup. It happen to have a premium cap with brass connectors and 8mm wires already on it.
Another great thing about GM parts is nearly any parts store you walk in will have replacement parts for you, in stock. That isn't always the case with Jeep parts. This is real convenient if you have a problem in a small town.
When you take out the old distributor, make sure you note where the rotor is pointing. It is best to have it pointing to number one. I just turned my engine over with the starter with the coil wire off to get it pointed somewhere easy to remember. I pulled the old distributor, did the gear swap, and slid the HEI distributor in. Sometimes it takes some jiggling to get the the gear and the oil pump lined up properly. There should not be any need to force it.
When you look at the Prestolite and the big cap HEI side by side, they look exactly the same on the bottom except for the distributor gear. The distributor gear used on the Chevy 250 is cut in the opposite direction from the AMC gear. A hammer and a punch are used to drive out the pin that holds the gear on both distributors. The AMC gear is a little taller than the GM gear and you cannot just install the gear on the distributor. Just grind the gear down a little bit so it will install on the HEI. The shaft of the distributor should turn easily and there should not be a lot of up and down movement on the shaft.
You don't have to grind the old gear down if you don't want to. I was just reluctant to throw a lot of money at the 258 in my truck since it has 185,000 miles on it. You can buy the distributor gear from an '83 and later AMC V8 engine part number 3208615 and this gear will slide right on.
I bought the distributor with the wires from the 250 and they didn't charge me extra for them. They happened to be some nice 8mm wires and they worked perfectly on my 258. Larry Maggio reports he used wires from a '77-'83 Ford Fairmont with 200 I6 engine and they worked well. The firing order on the 258 is 1-5-3-6-2-4.
I used a test light to figure out which wire was the hot on run wire to my Prestolite ignition module. I cut off the old plug and soldered on a wire with a spade connector. This wire just plugs into the HEI. All the other wires that went to the ignition module, I just wrapped up in some electrical tape. I don't have a tachometer, so I didn't wire that up.
I ran a fresh piece of 5/32" vacuum hose for the distributor advance. All the vacuum hoses on my J-10 were old and cracking, so it was well worth running some fresh vacuum hose. Make sure you hook the hose up to ported vacuum which is high at wide open throttle and low at idle.
After the distributor is in and wired up, your Jeep should fire up. If it doesn't fire up, take a wire off, put a spark plug on the wire, hold the plug to ground and get someone to crank the engine so you can verify there is spark. If you don't have spark, something is wrong with the wiring or the distributor.
If you have spark, something is probably wrong with the timing. You may need to statically time the engine. Remove the 12v wire to the distributor and take out the #1 spark plug. Get the #1 piston to the top with the starter or by turning the engine over with a wrench. Remove the distributor and get the rotor pointed to #1 wire on the distributor cap. Replace the #1 spark plug and 12v lead to the distributor. If it backfires, it may be 180 degrees off. You may have the wires on wrong on the cap or pull the distributor and turn it 180 degrees.
When I first did an HEI swap on my CJ-6 a couple years ago, I read Jim O'Brien's and Larry Maggio's articles. I can't seem to find Jim's article anymore, but Larry's is still out there and worth looking at since he has some extra information on his.
One other note, there is no reason this swap should not work on an AMC 232. The 232 uses the same distributor as a 258.