babbah

I have a new MSD 8572 Tach Drive w/ Vac Advance Can Distributor that I have installed in my 1967 Vette Big Block. The engine is modified with a long duration cam. I changed the can to the Echlin VC1810 that gives me vacumm advance at my idle of 8".

My problem is that I run the factory ignition shield and the vacuum can is positioned all the way clockwise against it. I need a tad bit more rotation in this direction to retard the timing about 2-3 more degrees. If I rotate the distributor in the other direction, it advances the timing. Then I reinstalled it and moved the rotor one tooth counterclockwise back and the can had to be all the way to the right - Couinterclockwise and the can is at the other side against the intake manifold.

I have already tried to install the distributor with the can initally in the "middle" of the opening between the ignition shield and the intake, at (16 degreess advance - degreed balancer) where the can should be and I can't get the motor to start. So I advanced the rotor gear one tooth clockwise where it is now and it starts right up and runs very cool. This motor likes at least 16-20 dgrees initial advance, due to the cam.
I run the black bushing in the 8572 providing 18 degrees total distributor advance.

I just can't get the vacuum can in the middle of the area that is provided with the igntion sheild installed, which I need to keep installed on the car.

I have read articles that sometimes the distributor gear is installed from the factory incorrectly and now I am wondering if I remove the distibutor gear and rotate it and reinstall it will this have any effect to help me with my problem? Does this make a difference?

I read that one tooth equals 28degrees of timing, so Im wondering what exactly my problem is here? Ive tried everything to get this right and its been frustrating...Should I pull the distributor gear off and rotate it and reinstall? Will this make a diiference? I read about the chevy magnetic distributor that it had a dimpl on the gear that aligned with the roll pin the rotor firing position and if the distributor gear was not installed correctly the timing was effected. HAd something to do with where the gear teeth were aligned in relation to the cam gear.

What are your suggestions?

Vette-66

Seems the 28* may be a bit off, if you divide 360 by 28 you come up with 12.8 teeth, dont think that is possible..
if you have 12 teeth on the dist then the each tooth would give you 30 degrees.
There is a dimple on the TI dist gear and this dimple is to line up with the # 1 fireing position. When I re-did my dist last winter I found I had it install all these years with the dimple 180 from #1 and YES the vac can now resides in a different location that it use to.

This may help you if yours is 180 out.

Hope this helps,
Chuck

SWCDuke

Rotating the OE drive gear changes the shaft position half a tooth and there are 13 teeth, which is about 28 degrees, and half is about 14 degrees. That's how much distributor clocking changes when you rotate the gear 180 and reinstall the dist. with the same initial timing.

Apparently many aftermarket distributors don't have dimples. I'm glad I don't have to deal with them, and another reason why I think they are junk!

In this case the individual can pull and reindex the distributor one tooth fore or aft as required to try to achieve proper clocking for the vacuum can in the range of proper initial timing. If this does not get the vacuum can into the proper position, pull the distributor, rotate the drive gear 180 degrees and try again. It will probably then be in the correct postion.

Mark the dist. drive gear with a centerpunch for future reference.

Duke

Ironcross

And normally very expensive!