Build a Crank Trigger Distributor

Crank Triggers are a very effective way to light the fire in your performance engine. So much so that auto makers adapted the idea to just about everything you have driven since around the year 1995. They use a sensor lined up with a reluctor wheel mounted either on the front or rear of the crankshaft. Timing indication from this location is far more accurate and precise that picking it up from the distributor. Now of course modern engines have either a short coil-to-plug wire or are of the coil-on-plug ignition, all electronically fired from information provided to the computer.

Crank Trigger ignitions for older performance engines have been around for years and normally when a hot rodder puts one of these on their engine, one of the steps is to lock out any advance mechanism on the stock distributor. The distributor essentially becomes nothing more than a “distributor” of the spark energy. This will work just fine as long as the distributor is in good shape and not worn out or sloppy in it’s clearances. In my particular case, I am building a new engine up from bits and pieces and did not have a distributor to start with but looking at the current prices of a crank trigger distributor will make you swoon. Average prices are running between $250 – $350 for a distributor. I will admit it is take it out of the box and drop it in – but where’s the fun in that?

So,, doing a little bit of shopping and spending a touch less than $125 I have a brand new, crank trigger distributor. And I am going to tell you how you can have one too. Now admittedly I am building a Big Block Chevy, if you have a Chrysler or Ford engine or something else, you have a bit more homework to do, but the principle idea is the same.

I started off by looking for a NEW – not rebuilt point style distributors for Chevys. I finally found what I wanted from Rock Auto Parts. A brand new, mid-60’s distributor was available for slightly less than $50. Moving over to Jegs, Summit and don’t ever forget Amazon, especially if you already have Prime membership, I started looking for a MSD Cap-Adapt setup. I prefer these as they allow you to run the larger Ford style distributor cap which spreads out the spark, plus it comes with a spark plug wire retainer system that is a simple, two screw system. The adapter also creates a larger air center which helps reduce the izonation of the air particles within the cap. Each of these items helps reduce or eliminate misfire. And we don’t like our engines to misfire do we?

The next two items on the list kind of go hand in hand but one of them might not be needed for your setup. I am running a Crane mechanical roller cam in this engine and need the bronze distributor gear that works with that type of camshaft. If you are running a standard type production cam or an aftermarket unit that is a hydraulic or mechanical flat tappet cam then you can keep the stock style gear and save a few bucks. You also want to setup the end play on the distributor and will need a shim kit – I went with the Moroso version as I had used their kit before and knew what I would be getting. I ended up setting this distributor up to .014 clearance but anything between .010 and .020 should be good. I am also getting ahead of myself a bit but that’s okay.

With all of the parts gathered up it is actually time to start tearing stuff apart. All of the following can either be deep-sixed or passed along to someone that still deals with points style distributors. The cap, rotor, points, condenser, vacuum advance canister, all of the wiring, the mounting plate for the points and condenser, the advance weights, advance springs and the advance/points cam all have to go. I didn’t bother to weigh all of this stuff but there’s bound to be at least a pound of stuff here. Now to get some of these parts off, you probably already figured out that you need to drive out the roll pin on the distributor gear, remove it, the spacers and pull the shaft from the distributor body. And this is where a welder will come in handy although it is not absolutely required. You will notice with the shaft removed that the advance plate/points cam is a separate piece. You need that piece to hold the rotor in place so I recommend that you fit it back to the main shaft and then on both sides of the oval shaped piece at the top, you tack weld the shaft and the advance plate together. Lacking a means of welding, you could also drill the two pieces and insert a small bolt/nut to lock them together. I have not done this myself so you will have to determine exactly where you can put the bolt without interfering with the rotor button attachment.

Once all the junk is out of the way, you can put a little bit of grease on the shaft, slide it back in and start figuring out how many shims you will need to tighten up the clearances. For the most part, this is a bit of trial and error, but one thing you can do is find a punch that has the same diameter as the roll pin and put that in place to hold the gear on while you check clearances with a feeler gauge. That beats driving that roll pin in and out.

With the clearance set, the next step is to install the MSD Cap-Adapt System. Rather easy as the main part of the system aligns just like the original distributor cap and and is held in place with the same type of push and turn 90 degree arms. Now you can mount the MSD rotor button in place but first check the clearance on the center part of the rotor. MSD now includes a cardboard guide that is sort of a go, no-go type gauge. I found my latest one to be bent down a touch too far. New MSD kits have a couple of choices for holding down the rotor button now, I decided to use the Allen head bolts that came with the kit. And finally the last piece is the Ford style distributor cap. Align the tab and snap the spring metal retainers in place and you’re finished.

What you now have is a fully “functional” crank trigger distributor. Which really kind of makes you wonder why they charge so much money for the darn things. When using a crank trigger setup, the distributor has one job and that is to distribute the voltage out of the coil coming into the center terminal of the cap to the terminals of the cap that are connected to the spark plugs. That’s it. No timing function, no dwell settings – nothing. When setting up your crank trigger, you will set the timing by moving the pickup in relation to the magnet on the crank mounted wheel. You will install your distributor so that you are lining up the rotor pointing to the selected spark plug terminal of the cap. A better way to determine that this is as precise as possible is using “Rotor Phasing”. Search that phrase on the Internet for additional information.

So there you have it – a quick and easy build that saves you at least a $125. Plus you probably had a little bit of fun with the build and you can be absolutely certain that you are going to get the maximum amount of power from your crank trigger setup.