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This is a 1972 with a cable driven tachometer.
Do you realize the damage that can be done to the cable if it is bent too much due to incorrect alignment of the distributor?
Chevrolet even created a service bulletin concerning the correct positioning of the distributor just for Corvettes to prevent cable damage and to still be compatible with the factory metal shielding.
And just to add some detail for anyone coming to the thread for information, the vacuum canister needs to point pretty much directly out the passenger side of the engine -- behind the tall spark plug wire bracket. This allows the tachometer cable to have a smooth S-curve rather than two much tighter bends if the housing were to be installed such that the vacuum can points more conventionally toward the passenger front tire.
On my 454, this orientation is very limiting in the amount of housing rotation to time the engine. I monkeyed around resetting the distributor to mate with the cam for quite a while until I came up with a compromise position that allows my timing to be correct while not jamming the vacuum hose into the wire support.
Last edited by barkingrats; Mar 22, 2021 at 03:56 PM.
OK. I’ll bite. What other variable is there? It seems to me that as long as the cap is rotated to establish correct timing, it’s all good. The relationships of all the internal parts are fixed.
Ok.
Cap looks perfect, check.
Vacuum Canister looks perfect, check.
Where is the rotor? Off one tooth?
Speaking of distributor positioning, here's a photo of a 1971 350 that sold on BAT on 3/3/21. The seller insisted that the shield support was not cut to accommodate the vacuum advance vacuum line. Also, notice that the distributor cap window cover was removed.
This gem has that awesome square bore to spread bore carb adapter too......gotta love that fuel line as well.....
Some people need to stay away from cars all together.
Been talked about before, but C3s need distributor oriented as per diagram below. Also, if the dimple on the distributor gear is not lined up with the rotor (180 degrees opposite), it will affect the distributor orientation as well. BAT car had the Bubba fix.
Ok.
Cap looks perfect, check.
Vacuum Canister looks perfect, check.
Where is the rotor? Off one tooth?
I have to admit - I had to go out to the shop and look at a spare distributor to check this out. And I looked at an HEI but I don't think a points style distributor would be any different. There are eight points on the star wheel on the distributor shaft which correspond with the eight points on the reluctor wheel. There are also eight terminals on the distributor cap. I cannot see how it is possible to install the distributor such that it would fire when the rotor is not aligned with the cap. Am I missing something?
What I am getting at and maybe not very clear, is that if your timing light displays a TDC or a ATDC the rotor is off one tooth. Regardless if the cap & Vac canister are visibly perfect.
The O.P. pulled out a distributor. The O.P. stabbed in a distributor. Then finds the timing marks all over the place, mostly ATDC.
Last edited by HeadsU.P.; Mar 24, 2021 at 09:23 PM.
Originally Posted by HeadsU.P.View Post
Ok.
Cap looks perfect, check.
Vacuum Canister looks perfect, check.
Where is the rotor? Off one tooth?
I have to admit - I had to go out to the shop and look at a spare distributor to check this out. And I looked at an HEI but I don't think a points style distributor would be any different. There are eight points on the star wheel on the distributor shaft which correspond with the eight points on the reluctor wheel. There are also eight terminals on the distributor cap. I cannot see how it is possible to install the distributor such that it would fire when the rotor is not aligned with the cap. Am I missing something?
Trying to understand your question DRW. Not sure if I do. I think what what Heads Up is saying is, if you want to orient the body of the distributor as per Chevy bulletin where the vac can points roughly to the rear of the right valve cover, you need to first drop the distributor body and engage it with the oil pump shaft. Move the distributor clockwise or counterclockwise so the rotor lines up roughly with terminal number one on the cap. If the vac can is not pointing to the rear of the right valve cover, the rotor will need to be adjusted by moving it one tooth or more where it engages the cam distributor gear. Usually involves removing the distributor, then using a long screwdriver to move the oil pump shaft gear, and reinstalling the distributor. Trial and error. Since the distributor gear has 13 teeth, the factory put a dimple on the distributor gear, and the dimple should be lined up with the rotor. Distributor will still work if gear is installed 180 degrees off, but could affect where the vac can points slightly.
Dimple on bottom. Should line up with rotor. Roll pin on top.
Trying to understand your question DRW. Not sure if I do. I think what what Heads Up is saying is, if you want to orient the body of the distributor as per Chevy bulletin where the vac can points roughly to the rear of the right valve cover, you need to first drop the distributor body and engage it with the oil pump shaft. Move the distributor clockwise or counterclockwise so the rotor lines up roughly with terminal number one on the cap. If the vac can is not pointing to the rear of the right valve cover, the rotor will need to be adjusted by moving it one tooth or more where it engages the cam distributor gear. Usually involves removing the distributor, then using a long screwdriver to move the oil pump shaft gear, and reinstalling the distributor. Trial and error. Since the distributor gear has 13 teeth, the factory put a dimple on the distributor gear, and the dimple should be lined up with the rotor. Distributor will still work if gear is installed 180 degrees off, but could affect where the vac can points slightly. .
The issue is only whether the distributor can be installed 'one tooth off'. I have done this hundreds of times and I don't see how installing the distributor one tooth either way affects anything but the orientation of the cap. (Assuming the distributor gear is installed correctly.) It seems to me that the distributor can be installed in any position that suits the vacuum advance and tach cable, and as long as the timing is set correctly and the spark plug wires are installed to the appropriate terminals, it will work. If that's not true, I've been incredibly lucky for about 50 years.
The issue is only whether the distributor can be installed 'one tooth off'. I have done this hundreds of times and I don't see how installing the distributor one tooth either way affects anything but the orientation of the cap. (Assuming the distributor gear is installed correctly.) It seems to me that the distributor can be installed in any position that suits the vacuum advance and tach cable, and as long as the timing is set correctly and the spark plug wires are installed to the appropriate terminals, it will work. If that's not true, I've been incredibly lucky for about 50 years.
Yes, you can install it one tooth off, or 2, 3, 4, etc, and it will still start, run and allow itself to be timed just like a conventional installation. The only catch is that you have to rotate the distributor housing to whatever degree required to align the rotor with the #1 cap tower. To add to the melee, you can also decide to use any cap tower you want as #1. As long as the firing order is maintained and the distributor body can be rotated adequately you can get it to run perfectly.
Yes, you can install it one tooth off, or 2, 3, 4, etc, and it will still start, run and allow itself to be timed just like a conventional installation. The only catch is that you have to rotate the distributor housing to whatever degree required to align the rotor with the #1 cap tower. To add to the melee, you can also decide to use any cap tower you want as #1. As long as the firing order is maintained and the distributor body can be rotated adequately you can get it to run perfectly.
This is all a person needs to know, (assuming they understand the distributor-shaft-to-distributor-housing relationship).
Once the timing is set correctly, (engine runs well), and regardless of the distributor (housing/vacuum can) orientation, the assembly can be "walked" in either direction to correctly position the housing/vacuum can. An easy way to avoid this in the future is to mark the distributor housing position as it relates to the intake manifold AND the rotor orientation as it relates to the distributor housing. BOTH must be accurately marked. (If it's a points-type distributor, a continuity meter can also be used to denote the moment of point break, bearing in mind that a distributor stab might wind up on top of the oil pump drive as opposed to be fully engaged, [not a biggie, just be aware]).
This was a total non-issue w/the old dual point, non-vacuum advance distributors.
Yes, you can install it one tooth off, or 2, 3, 4, etc, and it will still start, run and allow itself to be timed just like a conventional installation. The only catch is that you have to rotate the distributor housing to whatever degree required to align the rotor with the #1 cap tower. To add to the melee, you can also decide to use any cap tower you want as #1. As long as the firing order is maintained and the distributor body can be rotated adequately you can get it to run perfectly.
Thank you for confirming that. I was pretty sure that was the case, but I'm always willing to learn something new. (Although not always able. )
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