Ray's Chevy Restoration Site -- HEI Conversion HEI Distributor Conversion This page describes the installation of a GM HEI (High Energy Ignition) electronic distributor in my '74 Nova with a 350 small block. With the exception of firewall clearance problems in various vehicles, this should apply to swapping most any GM points type distributor to HEI. Some benefits from the HEI swap include reduced maintenance, easier starting, and often a small improvement in gas mileage.
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Finding an HEI Distributor There are a couple of choices here, new or used. If you go the used route as I did, it's a good idea to re-build it. In addition, here are a few things to note: • '75 to '79 ('75 to '85 Canadian) used 4-pin modules. • Some later models used a 5-pin module (for a knock sensor) • Computer controlled engines used a 7-pin module When replacing a points distributor, you should use a distributor with the 4-pin module. You could also use a distributor with a 5-pin module and replace the module with a 4-pin one.
That would require plugging the extra hole in the housing where the connector for the knock sensor wiring used to be. Distributors using 7-pin modules can not be converted to non-computer controlled use since they do not have advance mechanisms (they use the computer to control the advance). Also note that different GM divisions used distributors with different shafts and gears. So make sure that your used distributor came from the same type of engine that you plan to install it in.
Chevy 350 Distributor Installation
Rebuilding a Used Distributor If you choose to re-build a used distributor, here's a few suggestions/ideas: • The drive gear is held on by a roll pin -- carefully drive out the pin with a drift punch to remove the gear. • Once the gear is off, the shaft should slide out. If it doesn't, there is probably some rust or sludge build up on the shaft. Soak with penetrating oil and work carefully to avoid damaging the bushings. • With the shaft out, the pick-up coil and pole piece assembly can be removed by carefully removing the snap ring from the upper end of the bushing. • Once the distributor is fully dis-assembled, thoroughly clean everything. Note that there is a lubrication well surrounding the upper bushing.
Carefully remove the plastic cover and clean out the old (usually dried up grease) and replace it with new grease. I use wheel bearing grease. • Inspect for damage (particularly the pick-up coil & wires) and replace parts as necessary. • Slide the shaft into the housing and check for excessive play between the shaft and bushings. New bushings (or another housing with better bushings) may be necessary. • Note that most gears have a little dimple on one side that should be aligned with the rotor when the gear is re-installed. • After re-assembly of the gear on the shaft, slide it end-to-end and use a feeler gauge to check for excessive end play.
Use shims as necessary to get the axial end play near 0.015'. • Also check the mechanical advance and make sure that it is working freely. • The factory advance in HEI distributors used very stiff springs resulting in a very slow mechanical advance. Pick up an advance curve kit that contains various springs so you can experiment with re-curving the distributor. The weights that come with many kits are of questionable quality. I prefer to re-use the original GM weights.
• Apply thermal heat sink compound (not dielectric grease) to the underside of the module before screwing it to the distributor housing. Many new modules come with a packet of heat sink compound. It's also available at Radio Shack if you're re-installing a good used module.
• Finally, finish the re-assembly with a new rotor and cap. Rebuild Parts The following is a list of part numbers for items that may need to be replaced when rebuilding a distributor.
These parts are available at most any auto parts store. The part numbers listed are for the 4-pin module Chevy V8 distributors. Parts listed in red should definitely be replaced when rebuilding an old distributor. Parts listed in blue should be tested and replaced if necessary. And parts listed in green are usually only replaced if missing or obviously damaged.
Part Number Source: Standard Ignition Engine Management Parts Guide Catalog.
Firing Order for small block chevy engines OK, so you've done a tune up on your chevy small block V8 in your classic chevy and now it runs really bad. In fact it is missing so bad it will barely run and you suspect the firing order is off. You are sure you moved the spark plug wires from the old distributor cap to the new one, one-at-a-time. What could be the problem? I did it Myself! With Tools and Instruction from Seasoned Pros. They'll be in awe of you.
When you tell them who did the work. How to correct firing order on your chevy small block First, this document assumes you have not removed the distributor from the engine. If you have, you will need to bring the engine to TDC or 'Top Dead Center' in the firing position for the number one cylinder, then reinstall the distributor so that the striker on the distributor rotor is in the 6:30 position, detailed later in this document. There is a trick to this, but that is another document altogether.
Something for you to note. The firing order for the classic chevy small block with a breaker points ignition is no different than the newer HEI electronic ignition.
The only difference is that the number one firing position on the HEI distributor is in the 5:30 position such as the one on my 86 GMC pickup with a chevy 305 small block. Well, it makes sense at this point to just run through a systematic check of the distributor wires on your chevy small block V8 engine to be sure the firing order is correct.
454 Distributor Install Diagram
We may run into the cause of the problem by simply verifying the spark plug firing order on the distributor cap. Most likely there are two spark plug wires in the wrong position on the distributor cap and now the firing order is off. Which chevy small blocks does this work on?
This method is good for the firing order on all chevy small block v8 engines from 265 cubic inches to 400 cubic inches. This would include 265, 283, 305, 327, 350, 400 cu. Chevy small block v8 engines. Let's cover some safety concerns first. If you try to troubleshoot a mixed up firing order with the engine running, you could be in for a serious shock. You can do it, with certain precautions, but you really don't need to check the firing order with the engine running.
You definitely don't want to try checking the firing order if you are wearing any kind of pacemaker or sensitive electromechanical prosthesis. The voltage coming out of the ignition coil is in the thousands. Common sense dictates that you wouldn't stick a knife in an electrical outlet, so you wouldn't want to take chances with being shocked by the electrical discharge from your classic chevy's ignition coil either. How do I find the distributor?