mixalive

Since the harmonic dampener is the odd size of 7.0625 inch, no one seems to make the correct timing tape. So I downloaded the degree wheel and timing tape images off the web. I resized the print of the degree wheel until it was the same size as my harmonic dampener. I then printed the timing tape and compared the marks with the degree wheel, adjusting the size of the timing tape print until it matched the degree wheels marks.

mixalive

Building a pointer was pretty easy. I used some scrap 1/8” thick 5052 aluminum and cut to the shape of the image below. I cut it with a jig saw and filed it straight. So, the bracket is going to mount on the bottom 1/4” bolt that holds the Optispark to the engine. You need to determine the distance from the mount point forward to determine where you need to bend the bracket 90*. Once bent, you need to determine where to drill the 1/4” hole so the bracket is off of the dampener. Drill the hole, mount the bracket, and take a scribe, and scribe a mark on your new bracket against the Optispark mount bracket. This will be the point where you mount a stop on the bracket to prevent it from moving and to make a consistent mount point when removing. I tapped two 10/32 holes in my bracket to hold a stop, fitted it and red Loctite’ed the stop down. Remount the bracket to the Optispark and you are done with the bracket setup. You then determine top dead center and glue the timing strip to the harmonic dampener.

mixalive

I borrowed this from another post by Icvette. He is an expert.

To determine Top Dead Center, you need to remove the number one spark plug, use a spark plug hole piston stop and turn the motor until it stops against the piston stop. At this point you need to add some form of stationary pointer to your engine near the harmonic dampener that will be visible with a timing light from above the motor. Doesn't matter where the pointer goes as long as it is sturdy and will not move on you!

Once the pointer is installed, make a mark on the dampener where it is pointing too. Now, turn the engine over the opposite direction until it again hits the piston stop. Again make another mark on the dampener where the pointer is pointing to.

Now, the center position between those two marks you just made is true TDC for the #1 cylinder and is what everything in your ECM is calculated off of including ignition timing, fuel injector timing etc etc.

bjankuski

Perfect. This is what you need to do to tune an LT1. I do this on every LT1 I tune that has non-stock parts in it and sometimes the timing is way off. At least if you know what the actual timing is you can either tune for the error or fix the error with the adjustable MSD.

carguy604

Hell, yes! What's the cost to make me one?!

dizwiz24

This is a very cool part. Thank you for sharing.

I use tunerpro RT, $DA2 definition, and a Moates ostrich to modify my timing on my 93 (vs. an adjustable distributor).

However, it'd be nice to actually 'check' that the timing is where it says it is.

I also have a MSD-6BTM distributor which is supposed to take out timing in response to boost depending on where you have the dial set at (adj. 1 to 3 deg retard per psi boost).

This method you have proposed (along with a Mity-Vac attached to the boost hose) would allow me to actually test out whether that MSD-6BTM does what its supposed to.

This boost retard would be my only line of defense against detonation if I wasnt already doing it through my tune or meth/water inj.

I do want to warn the OP:

if you have an MSD optispark (thats the only one I know thats adjustable).

You will find that many users here got a bad MSD and had to swap it out with at least one other MSD optispark before getting one that works right. Sometimes it was bad right off the bat. Other times it lasted up to 3000 miles then went bad.

The only optispark distributor that works reliably out-of-the-box are the OEM models. The rebuilds (even AC Delco 'remanufactured), knock-off's, dynasparks, etc. all do not have the reliability of the stock optis.

This is not a part that you want to fail on you in a traffic jam, busy highway, etc.

mixalive

I updated the images and measurements on the first post for you guys.