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Discussion Starter · #1 ·
Recently I have seen more than one "expert" on TV say Chevrolet distributors should be installed with the rotor pointed at the #1 cylinder with the engine at top dead center. This isn't the way Chevrolet did it and in fact it's one tooth off. I am now seeing this bad information repeated on this forum.

There are 13 teeth on a distributor gear and you can drop a distributor in randomly in any of the 13 positions and make it run by moving the wires around on the cap. You can get it to run but it isn't correct.

Here is how to install your distributor like GM did it.
  • Rotate the engine until #1 cylinder is at the end of the compression stroke at top dead center.
  • use a long screwdriver to position the oil pump drive slot parallel to the engine center line
  • Drop the distributor in with the rotor pointing directly forward (it will rotate clockwise as it drops in)
If the distributor doesn't drop all the way in make a slight adjustment to the oil pump drive and try again. I have been using this method for over 40 years. I have also noticed that distributors "installed a tooth off" end up with the vacuum advance can in the wrong position. Sometimes the vacuum advance can will bump against the intake manifold or valve cover making it impossible to correctly set the timing. A correctly installed distributor will allow the maximum amount of timing adjustment.

For those that still think the rotor should be pointed at the #1 cylinder here are some pictures from the 1956 Chevrolet and 1967 Camaro assembly manuals. I have also included the 1967 big block page as the big block distributors are installed exactly the same as a small block.





 

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I think most of us have figured out it moves a tooth as it drops in. It’s not rocket science.
 

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One very large factor is just where the rotor should point to be at number 1. On small blocks, points distributors should point to the 5:00 o'clock position, large coil in cap, Chevrolet moved the rotor to the 7:00 o'clock position. Big blocks are the same.

"I think most of us have figured out it moves a tooth as it drops in. It’s not rocket science"

OH, YES, IT IS! Just WHY is this occurring?????

When a distributor is removed from a previously run engine, the oil pump has oil in it, and depending on how hot the oil is, the gears will actually move a bit reversed just after the drive shaft clears the oil pump drive slot. When this occurs, the oil pump drive shaft tang no longer aligns with the shaft on distributor replacement.at its former alignment

This also happens with any spiral release on tang and slot interfaces, with any device that holds liquids, and liquids that have viscosity. Even cold water can do same

There are various methods to correct this unintentional misalignment, long screwdriver down the hole to move the tang back to the proper alignment position, "bumping" the engine over, distributor with no gear on it down in and re-phase, and, more.

The one thing to do to attempt to not encounter this issue is to remove the distributor VERY SLOWLY, so the oil drag on the pump gears do not reposition the tang back from where it clears the shaft.

VERY SLOWLY.
 

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My dizzy (rotor) is installed per post #1. IMHO if it was installed so rotor points to #1 cyl....its a PIA to then get a wrench on the dizzy hold down bolt as the VA can is in the way from PS access.
 

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Hi Dave- glad you made it into rocket science. I knew you could.

I always bumped it in or turned the crank a bit.
 

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Mike
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With so many distributor caps now having male terminals on top (HEI style) and the 90° boots on the HEI style spark plug wires that connect to these caps, I think pointing the rotor towards the #1 cylinder at TDC (with the distributor fully seated onto the intake manifold) may have more to do with a personal preference for a cleaner/neater way to route the spark plug wires... especially when running an HEI distributor with tight firewall clearances. See example and explanation below.
275327

When the #1 terminal of the cap is in the 5 o'clock position and the rotor is pointing towards the #1 cylinder @ TDC (left image), 6 out of the 8 cap's plug wires will be routed to the same side of the block (#2 and #3 terminals will be on opposite sides of the corresponding cylinders)... and the 2 cap terminals closest to the firewall are on the same side as their corresponding cylinders.

When the #1 terminal of the cap is in the 7 o'clock position and the rotor is pointing towards the #2 cylinder @ TDC (right image), only 4 out of the 8 cap's plug wires will be routed to the same side of the block (#1, #2, #3 and #6 terminals will be on opposite sides of the corresponding cylinder)... and the 2 cap terminals closest to the firewall are on the opposite side as their corresponding cylinders.
 

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Gee, the above diagrams are EXACTLY what I described above them in my earlier post.

As far as the hold down bolt goes, there are nice bent boxed end wrenches to do the tightening, they clear the vacuum advance. And, if you simply rotate the distributor body so the vacuum advance goes twords the firewall, and out of the way, one can use a regular boxed/open end wrench until the bolt puts a bit of tension on the clamp, then rotate the distributor back to correct position, and final tighten after setting the initial timing.

Simple enough.
 

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Discussion Starter · #9 ·


Here is a correctly clocked distributor. Notice how the the vacuum can is at the correct angle. If you want to move the wires so number one terminal is pointing to number one cylinder you will need to move the rotor one or two teeth counterclockwise. Here's the problem. Each terminal on the cap is 45° apart, and each of the thirteen teeth on the drive gear is about 27.7° apart, so moving the rotor one tooth (27.7°) isn't enough and two teeth (55.4°) is to much.

Keep in mind that these are distributor degrees and not crankshaft degrees. Moving the rotor two teeth is closer but you will need to rotate the distributor housing counterclockwise moving the vacuum can towards the intake manifold and out of this ideal position.
 

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I see you fully believe this is the ONLY position the vacuum advance can sit when timing is correct. Well, news flash, with all the different timing scenarios used on GM small and big block, vacuum advances can end up a few degrees EITHER DIRECTION from your only one perfect position. It doesn't take a trig genius to figure that out,
 

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I see you fully believe this is the ONLY position the vacuum advance can sit when timing is correct. Well, news flash, with all the different timing scenarios used on GM small and big block, vacuum advances can end up a few degrees EITHER DIRECTION from your only one perfect position. It doesn't take a trig genius to figure that out,
I think you are missing his point. Might want to try and re-read his post again....
 

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We need the BB 4-7 swap crowd to weigh in now to add more clarity????
 

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Mike
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We need the BB 4-7 swap crowd to weigh in now to add more clarity????
Following the logic of post #7... the rotor could point towards #8 cylinder @ #1 TDC
... or towards the firewall @ #1 TDC.
275371

... but I don"t think I'm helping out with the clarity :)
 

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I've owned and used this distributor wrench for years. No more access problems or hot fingers.
Yup, I have the same thing. Bought it brand new 30 years ago from the old Snap On warehouse a couple towns from my house. Worth every cent, especially back then when I was using it on 4-5 vehicles at that time. For those interested, look for Snap On # S6909 on ebay or from here: Snap-on Store
 

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As far as the hold down bolt goes, there are nice bent boxed end wrenches to do the tightening, they clear the vacuum advance.
I've owned and used this distributor wrench for years. No more access problems or hot fingers.
I also use a distributor wrench to loosen/tighten the distributor clamp hold-down bolt. This tool has both 1/2" and 9/16" 12 pt boxed end wrench sizes. The knurled adapter connects to a 3/8" ratchet... or just install the other portion of the wrench into the adapter to use as a handle. Probably one of the first tools I purchased over 40 years ago. Only $8-$9 at most auto parts stores.
275376
 

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Discussion Starter · #18 · (Edited)
One very large factor is just where the rotor should point to be at number 1. On small blocks, points distributors should point to the 5:00 o'clock position, large coil in cap, Chevrolet moved the rotor to the 7:00 o'clock position. Big blocks are the same.
So are you saying Chevrolet installed all points distributors with the rotor pointed in the 5:00 o'clock position? Well, news flash, every piece of literature I have ever seen says that isn't true. Here are a few examples.
http://www.567chevyclub.com/images/Team_Camaro/1955-distributor.jpg
http://www.567chevyclub.com/images/Team_Camaro/1969-distributor.jpg

How about that. The assembly manuals from 1955 and 1969 both show number 1 at 7:00 o'clock.
 

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So are you saying Chevrolet installed all points distributors with the rotor pointed in the 5:00 o'clock position? Well, news flash, every piece of literature I have ever seen says that isn't true. Here are a few examples.
http://www.567chevyclub.com/images/Team_Camaro/1955-distributor.jpg
http://www.567chevyclub.com/images/Team_Camaro/1969-distributor.jpg

How about that. The assembly manuals from 1955 and 1969 both show number 1 at 7:00 o'clock.
I agree, the 7 o'clock for #1 is what I was taught and every engine I ever worked on had it at that same 7 o'clock. I just couldn't find any documentation to show that was the correct way. Thank you for finding those links.
 

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All car guy should have that dizzy wrench, mine for 50 years or so. Its amazing my cars run fine with #1 pointing to #1 cylinder.
 
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