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Thanks again... I just took apart that spare dist to see how it goes together.. Not a big deal as you said.. Just picked up a Morison shim kit and Mr gasket spring and bushing kit today... Will get a reading of the initial , mechanical, and total timing of the car in a few days... I'm hoping that the dist in the car is just missing the limit bushing.
The limit bushing on the replacement dizzy I bought was missing and someone modded it by welding a bead on one end of the oval.
I filed the bead off to the original oval and pressed the bushing on the pin that came with the Mr. Gasket kit.
Same thing here, if I ever get this engine back together I will run it and do the trial and error thing when I run it.
 

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Where is the distributor number located

Does anyone have a picture of where the distributor number is located.
I have an original AIR 1966 GTO built at the Fremont Plant and would like to check further into this topic that is on the workbench. - Thanks!
 

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Not sure on the '66 in '67 they changed from cast iron to aluminum and the # is stamped on the back side on the round part of the casting.
 

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The numbers on the older cast iron distributors are located on a red anodized aluminum band attached to the shaft. Easily lost/removed/changed. Sometimes there is also a number stamped into the body, but not often. As stated, that is more often the case with '67-up aluminum distributors.
 

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Discussion Starter #25
Hi everyone... I'm back at it again... Got frustrated with my tri power not running right. Took it to a local shop and they got it running pretty well. Carbs and idle good..... Only problem remaining is the total advance. They said it's around 48 to 50 degrees. To much, should be around 36 to 38. Said I needed a new dist. Thought I would either by a pentronics or rebuild mine with springs and bushing. Got nervous and bought a new oem rebuilt one from a local parts store. But I don't see a limit bushing. should there be one? I haven't installed it yet. My timing now is 6 1/2 degrees w/o vac initial. 19 degrees , jumping around a bit, w/ vac. and 29 degrees or so at 3000 rpm for, I think wide open total advance. If I add the initial w vac and the wide open advance I get the 48 degrees or so the shop said I have. Is this correct? and shouldn't it be around 36 degrees. Sorry guys, still a little confused about the whole thing. Recommendations requested! thanks....
 

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I am no expert on this, but maybe this explanation may help.

Total timing is WITHOUT the vacuum advance connected - so this must be disconnected and the hose end plugged off. So if you want 36-38 degrees total advance, this is a combination of where you set your timing mark on the balancer at idle speed, 12 - 14 degrees. The distributor has the weights & springs that add additional timing advance as the RPM's of your engine rise - this is called your advance curve. The rate at which the advance curve kicks in is based on how much tension the springs offer that are attached to the weights. There are light, medium, and high tension springs to "tune" your distributor's mechanical advance. These springs are purchased in kit form from aftermarket suppliers. Your factory distributor is set-up by the factory and should operate as the factory specifications call for. Any modifications to your engine can change the factory specs and this is where you play around with the springs/tension to adjust the timing curve that best suits your engine -and sometimes the gas/octane you are using.

The built-in mechanical advance in the distributor for a Pontiac should be around 24 degrees. Add your initial timing at idle, 6 1/2 degrees, and you get 30 1/2 total ( you won't get 36-38 total degrees setting the balancer at 6 1/2). To get 36-38 as you say you want, then you will have to set your idle around 12-14 degrees - which may be too much and cause hard starts, or worse, pinging/detonation which will damage your engine. So, if you set your balancer timing at 8 degrees, add distributor timing of 24 degrees, you get a total advance of 32, 10 will get you 34, 12 - 36, and 14 -38. You will have to play around with this.

Now the total advance can be made to be all in at 2,500 - 3,500 RPM's depending on the tension of the springs you use and how much movement your weights actually have. Aftermarket distributors offer more adjustments to include weight stops to dial in the mechanical advance. Factory distributors don't have this and fabrication of some kind is needed, but you have to know what you are doing.

Once you have your timing set, THEN you connect your vacuum advance and this can add up to 10-15 more degrees, but only when the car is cruising under part throttle.

Check out this website: https://www.msdperformance.com/support/set_your_timing/
 

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As Jim says, Check total advance with the vacuum disconnected. Then reconnect the vacuum. When cruising at part throttle, the total advance can exceed 38 degrees. I've seen 48 to 50 routinely. I don't worry about it. If you're at 36-38 degrees at ~3000 RPMs without the vacuum connected, your throttle response is good and you're not overheating in traffic (an indication of not enough advance), run it and enjoy it.
 

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Chuck, the gang is right. I was setting up a Pontiac distributor today, did my friends 65 corvette monday...it is really peppy now!

so i will attach some pics, you don't need a sun machine to do it but it is easier. So here is a rebuilt pontiac dist, centrifigal tested 30 degrees advance at the crank, this is weights only. Two much. Lots of them are like that. I used a piece of brass 7/32 hobby tubing and a hobby tubing cutter & made a bushing. The bushings in the curve kits are for racers and they take out two much advance. My bushing knocked centrifigal down to 26 degrees.just tested on my Sun machine. I will crimp it or put on a dab of glue, a c clip can work. A tip from Lars was to hit the bushing on it's side with a small hammer, a tap, which makes it snug on, as it is a little loose to start with. that makes a snug fit.

the hollow where the bearing slides was 9.6 or 9.7 mm, the bushing on the stem was 5.55mm....that gave me 26 on this distributor.

So I would set base at 10 for 36 total degrees.

next is vacumn can, hook it to full manifold vac, I just put in a B26 can which pulls 16 degree advance at crank...starts moving at 5hg all in at 13 hg,....my idle vac is 18hg and light throttle cruise about 16 hg..i have a vac gauge at dash.....so this gives me all the spark. Ifyou have vac at idle above 13 this is a great can and easy to get, Napa, oreilly etc.

this will give me 52 degrees at light throttle cruise, 36 total mechanical advance.

springs bring all advance in by 2900 RPM and starts at 800 RPM,...Idle is 550 in drive.

idle advance is then 10 base and 16 vac for 26 and it runs smooth as silk at that setting. I have an adjustable can in their now, a crane and I am going to take that out and use this other one.

main thing is read Lars timing papers and his advice on vac cans etc. If you set your cars up like he advises it will run cool and be very powerful and efficient.

you can check all that with a dial back timing light or timing tape...

Small bushing, a B26 can or one suited better, the right springs try the crane blue and silver, will get you pretty close...

Good luck some pics
 

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You might also consider a MSD Pro-billet Ready to Run distributor. It uses a magnetic trigger instead of points, includes a vacuum can and is maintenance free if set up properly. You can also run it with a MSD spark box, but that is not required. For originality you can substitute a black distributor cap for the red MSD cap. I run this distributor with the MSD 6AL spark box and a MSD Blaster 2 coil with MSD wires on my '65 GTO Tri-Power 389 WS. It's flawless.
 
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