Here is a great description of how to tell the difference between even fire and odd fire High Energy Ignition (HEI) distributors. A comprehensive description of how to convert your 225 V6 to HEI can be found HERE. This is article that was composed from a thread on the Jeepster Commando forum. I consolidated all of the pictures and captions with the permission of Tim who did the original work. Click on the thumbnail to get a larger picture.
An even fire and odd fire distributor with caps on. Note the two dummy plug wire towers at 2:00 & 6:00 on the odd-fire cap. No dummies on the even-fire cap.
Caps off. Looking straight down into the distributors. Note it is virtually impossible to tell if the distributor is odd or even at this angle. You need to see under the weights and shaft to tell. Looking at what’s inside the caps you can tell the odd from even by the three different size tangs that the rotor contacts of the odd-fire while the even-fire cap’s tangs are all the same size and evenly spaced.
Close-up of the odd-fire cap inside with three distinct sized tangs. Starting at 12:00, # 1 is long, #’s 2 & 3 are short, # 4 is long and #’s 5 & 6 are medium.
Close-up of even-fire cap. All tangs same size, equally spaced.
Shafts removed. Note the pickup, (the rings with inward pointing points), on odd-fire has six points spaced unevenly like three groups of two close together. Even-fire pickup has six evenly spaced points. Shafts are positioned upside-down to show differences in the reluctors, (star shaped piece with points facing out from the shaft). Note three evenly spaced points on odd-fire shaft, while even-fire shaft has six evenly spaced points.
Both odd and even-fire distributors take the same coil. Note the correct coil in the distributor cap compared to incorrect Chevy coil. Buick coil has red & white wires while Chevy has red & yellow. Buick also reverses polarity. The red & white wires are crossed, while the Chevy’s red & yellow wires are not.
Close-up of crossed wires on Buick coil reversing polarity. Sorry it’s not in focus.
Close-up of Chevy coils’ red & yellow wires coming straight out.
Shows new even-fire cap w/rubber-type washer, coil-to-rotor contact button & pkg. of di-electric grease. These should be the contents of either type of cap when purchased new. This is from NAPA.
Shows contact button inserted, (thus the X rating), with the spring up. Be sure to coat both sides of rubber washer with di-electric grease or coil could burn out.
Shows rubber washer placed over contact spring. Now it’s ready for coil and cover.
I would like to make special thanks to David Chun Sr. at Super Tune in Vancouver, WA, who helped me on his day off to disassemble, set up and filled me with all the information in this post. He has taught me quite a bit over the years and fixed countless problems I’ve had, but I learned gobs more on these distributors than before in just the time to shoot these pics.
Here’s a pic of a properly installed odd-fire HEI in a 225.