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Hagerty
Hagerty Employee

Looking for answers about mechanical ignition? Check out this FAQ | Hagerty Media

Because I get asked the same ignition-related questions over and over, I thought I'd take a moment and write up an FAQ. Obviously, there are some car-to-car variations, but the basics of distributor-coil-points-condenser are fairly universal.
https://www.hagerty.com/media/maintenance-and-tech/looking-for-answers-about-mechanical-ignition-che...
18 REPLIES 18
XXXMIKEXXX
Pit Crew

Very good information !!!!! I use points in my 1952 Chevy truck roadster!! Wouldn't have it any other way !!!
dhaugh
Intermediate Driver

Because I'm old and human I expected to read about mechanical injection and I was wondering why a distributor in the pictures, early Bosch type injection used a trigger board or even extra points to trigger injectors, but that's electronic injection, not mechanical. Reading a little more closely I realized it was ignition, not injection.

A couple of tips for checking key items on your distributor. First, if you have a vacuum advance or retard, check it by simply attaching a hose and sucking on it to see if it holds vacuum, the distributor plate should also move. Second, check to see the mechanical advance is working, grab the rotor and twist it, in one of the two directions it should move/rotate and then return back home on its own. Lastly, if your car runs like crap, wiggle the rotor from side to side, if there's movement you likely have bad bushings in the distributor causing all kinds of timing and dwell problems with each rotation. Rebush your distributor and your engine will run like a dream
thehackmechanic
Detailer

Excellent tips all, thanks.
964c4
Intermediate Driver

I was really hoping for an article on mechanical injection like the title says but when I clicked on the article link it comes up as mechanical ignition. Please consider doing an article on Kugelfischer and Bosch injection pumps in the future.
Al
Intermediate Driver

I too was looking forward to read about mechanical injection
GaryB65
Pit Crew

Rob, thanks again for another well-written, informative article. I'd like to add another important point about retrofitting a Pertronix-type ignition on a car with a resistor wire: the red wire to the module has to get a full 12+ volts to operate properly. With a ballast resistor it is easy to retrofit, just hooking the red wire to the 12-V input to the resistor. I did that on my 65 Corvette and it has worked great for over a decade. With a resistor wire you have to go upstream of the wire to get a full 12 volts. I finally decided to retrofit my 71 last year, and finding no ballast resistor I thought I was home free. But it turns out C3 Vettes have resistor wires which originate at the engine side of the firewall bulkhead, and travels to the coil through a wrapped wire bundle. I did not want to separate the 50-yr-old bulkhead and did not identify an alternate ignition-switched 12-V source under the hood, so I went back to points. I am open to any suggestions about a suitable power source, though.
Also, the kit I bought for the 71 is "WVE" brand from Rock Auto but has a Pertronix-brand pickup. The instruction for that kit lists 1.5 ohms as the minimum coil resistance, not 3.
thehackmechanic
Detailer

That is correct. If there's a ballast resistor, you want the red Pertronix wire to go on the input side of the resistor. I have yet to personally fit a Pertronix to a car with a resistor wire.
Swamibob
Instructor

Hey Gary:
I've installed lot of these, over the years, on GM vehicles. You can power it from the "R" terminal on the starter or one of the accessory terminals on the fuse box. Just make sure it's powered, both when the ignition is 'on' and 'start'. It works great.
hyperv6
Gearhead

Points are great if you want to relive the past like bias tires and vacuum wipers. For stock restorations they are fine. But if you plan to drive much the Pertronix unit will make life much easier.

If you are not stock it is full blown electronic ignition every time.

I saw mechanical injection. That belongs to the devil compared to the modern FI systems we have today. The adaptability of today’s units to temps and other factors just make them ideal.
Tinkerah
Technician

I have another technique for diagnosing mechanical ignition: with the cap off, bump the motor until the cam is at a point where you can open and close the points by twisting the rotor against the advance springs. With your test meter or light you can now troubleshoot the entire system in both open and closed states. With a plug in the coil wire resting against any convenient ground, you'll know you've fixed it when you hear that satisfying snap from the plug as you twist the rotor.
thehackmechanic
Detailer

Excellent, thanks. I'll add that one to my bag of tricks.
Tinkerah
Technician

My T-Bucket had started running poorly and I thought the voltage to the coil was low. Looking for the ballast wire I found the previous owner (who never completed the car) had folded it over itself and stuffed it into a section of corrugated wire loom. There it overheated and burned adjacent wires with it. I have a folder of hilariously incompetent blunders I corrected on this thing, this one is probably the least obviously bad.
thehackmechanic
Detailer

Wow, good catch!
DougL
Intermediate Driver

I remember the good old days, when condensers hardly ever failed! I understand it is common now. I only have one now, in a 53 Mercury. It's pretty old, it probably is OK.
Bmike
Detailer

I can testify to the quality, or lack thereof, of the newly produced condensers. In the course of bring a neglected Bug back to life, I installed all brand new ignition parts. Cheap insurance, right? After about 6 months of light duty, the bug sputtered and died in the drive thru. Very embarrassing. Oh Bosch, what happened to you?
Swamibob
Instructor

Years ago I ran into this problem with point sets from Filko; that used a built in capacitor rather than a separate condenser. The capacitors seemed to work for 10-15 miles before failing. I tried two or three before informing Filko that that idea wasn't a very good one. It wasn't long after that built in capacitor part numbers went away.
TonyT
Instructor

Your failure to mention MSD is noticeable. A -6 box is probably the most affordable performance improvement one can add to an older vehicle, and they can make spark plugs last much longer than just about anything else. And just to stir the pot a little, even today's ignition systems are still based on a mechanical principle: a reluctor that is rotated past a fixed pickup, either crank or cam driven.
JustinSchroder
Intermediate Driver

The ballast resistor bit is super helpful. Thank you!