Johnny BluePrint: How to Swap/Drop in Your New Aftermarket Distributor! And Verifying Rotor Position

  1. Johnny Mac
    So you've made the decision to upgrade your factory ignition, and you're holding a shiny new distributor from BluePrint Engines in your hands :) ! you're now ready to tackle the install!
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    This may seem a bit novice, but due to the immense of tech calls i have been getting on this exact topic, lets take it back to basics!

    BEFORE YOU START! Lets discuss a few things to make this easier

    Where and what are top dead center? (TDC)
    Top dead center is the spot in the engine cycle where the piston reaches its most upward travel in the cylinder. This can be verified in several ways!
    Your Timing mark on your balancer Should reflect TDC when it lines up with the 0 timing mark on your timing tab/cover.


    At this point/position. Your distributor rotor should be doing 1 of 2 things...Pointing directly at the #1 piston...or it will be pointing rearward toward the firewall. (On a Smallblock)

    This indicated whether you're on the intake or compression stroke of that crank rotation.

    to make it simple... bump the engine over until you have your balancer oriented as above...and you have your rotor pointing at your #1 cylinder, which will be your #1 spark plug wire terminal on the dist. cap.

    At this point..lets hope the zero marks lined up when the rotor was pointed at #1.
    You have now positioned your engine at TDC, with the rotor pointing at #1 for a great reference point for making sure your new distributor goes in the same position.

    *remember the above was done with an assumed assembled, running engine...

    Lets talk the famous 180 out scenario...real quick
    so far we're assuming you're not 180 out, because your engine was running... so we spin everything til the rotor points forward...the rotor points at #1, TDC on balancer you're not 180 out.

    But what about a fresh build, or you took zero note of the rotor direction? How do you know it's the compression stroke, and not the exhaust stroke?
    Place your thumb over the #1 plug hole and rotate the engine...when you feel the air push your thumb away...thats compression. so the rotor should be at #1 on that one...not pointing backwards.

    you can also pull a valve cover and watch the valve position, via the rocker to determine the stroke...but i'm assuming thats a bit intensive if we're having the rest of this conversation.

    so oh oh...

    when you line up your timing mark as above, the rotor is not pointing at #1. (or anywhere near it)..or this is even a freshly assembled engine, so it hasn't even had a distributor in it.

    if you don't verify compression stroke..again we have the "180 out" possibility...or your timing marks are off...or your oil pump driveshaft is not clocked properly, and/or someone moved your #1 plug wire to another terminal to make up for it.

    so now what... Well lets verify TDC the quick and dirty way. Pull the spark plug on #1 piston (and make sure your dist cap is off, or the coil wire is unhooked so the car doesn't try to start)

    (doing this next step by hand with a breaker bar on the balancer bolt is the preferred method)

    you then stick a small, rod down into the plug hole until its resting on the piston. Careful with metal as to not pinch anything...and careful with wood as to not leave splinters. With your rod resting firmly on the piston, rotate the engine over until the piston begins to move upward. It will slow, slow, slow, and then stop. and then reverse direction. The "STOP" is TDC.

    so..does your balancer mark line up at this point? They usually do as mopars are key-way balancers...but it doesn't mean someone didn't put a "timing tape" on incorrectly in the past, or the balancer has several marks...or no marks.

    THIS IS mark it on your balancer if its not already there.

    Caught up? balancer is marked and lined up with zero? that #1 piston is at its upward position?

    Back to the rotor... remember we only did this because it wasn't pointing where it was supposed to be.

    so now...lets fix the rotor position (since we are TDC on crank and verified compression stroke)

    Your rotor is pointing at the firewall: you are 180 out...spin the crank until the timing mark comes back around to zero. Is the rotor now pointing at #1? were 180 out.

    Your rotor is pointing some random direction:
    LETS LOOK AT YOUR CAP! the engine was running before anyways correct? does the #1 plug wire line up with where the rotor is pointing?

    If so...
    Scenario 1: your oil pump driveshaft (which has the distributor gear attached to it) became clocked in the wrong position when someone swapped distributors in the past.

    Scenario 2: you already have a non-stock distributor, and the rotor position simply differs from what the gears position was originally...and then someone just moved your plug wires around to correct it. (WE WILL COME BACK TO THIS)

    how to fix it...
    The good news is that your oil pump driveshaft is "clockable" meaning it can be spun BACKWARDS to "fix" its direction

    DO NOT!!!
    Try to spin it forward.

    BB and SB have opposite rotating look at the gear teeth to determine direction.

    This is not an extremely fragile process...with a simple fat straight screwdriver, the driveshaft will spin backwards won't want to spin forward.

    you spin it backwards and it will corkscrew upwards on the cam gear. away from the ground. Nothing "holds" it in place other than gravity.

    Note that as you spin it backwards, it rotates the "slot" in a circle. And as it drops back rotates back the other way. so it's a 2 steps forward, one step back kind of method, but you're making progress.

    Slowly rotate the gear, and let it fall, until the slot is pointing at #1. REMEMBER..we aren't spinning the cam or crank...just a pump driveshaft. which in turn is re-clocking the distributor shaft/rotor to actually point at #1 piston.


    you should have the rotor, and balancer, at TDC, on the compression stroke. at this point!

    SO! now we're ready to open that box with that new Distributor in it!

    Install...look at the rotor position relative to the slot/ keyway on your OLD distributor..make sure the rotor appears to point in the same general direction at the old distributor, relative to the slot.

    A Few Notes.

    It's not at ALL unheard of for an aftermarket distributor to NOT necessarily have the rotor aligned in the OE position. SO comparing your NEW unit to the OLD one is very smart...because say your new dist. has the rotor 90 degrees off/different, just due to a manufacturing process, and you blindly drop it in... You're back to the scenario above where the plug wire terminal/ #1 piston will NOT line up with #1 TDC on the balancer.

    IF your new unit isn't aligned with your current TDC/#1 position, follow the reverse gear rotation method above to clock the oil shaft gear to the needed position.

    So lets hope you caught this before you started... If you didn't, and now you're standing there with your old distributor already in the trash can...just confirm TDC like we discussed above, and make sure the rotor position matched the TDC mark on the balancer, and you'll be fine.

    If you already installed your distributor without checking any of the above (yes it happens daily) and now you wonder why it won't run, or why it's popping flame through the carb...then stop...and verify the above.

    They clocking of the oil pump drive shaft is something that we encounter regularly because simply...these cars are old, and they have been apart, and have parts replaced 500 times over the years.

    I will note also that Most of the #1 distributor position reference above is assuming smallblock. (pointing at the #1) on a BB, the distributor is obviously tilted. Just remember your #1 wire/ going to be whatever post the rotor is pointing at when the #1 PISTON is at TDC.

    This should be a good read for someone that may save them a phone call after they hastily pulled out the old distributor, threw it on the bench, dropped in the new one, googled the plug wire diagram, and is now wondering how they have a "bad distributor"

    Hopefully this helps someone. and saves a few phone calls! :)

    any questions, comments, or other tips feel free to add!

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