After reading a lot of posts on reinstalling a distributor I am a little confused.

I always thought that you get the #1 cylinder to TDC, and when you drop in distributor the rotor should point to the #1 cylinder, if aligned correctly. Most of the posts say the rotor should align to #1 connector on the DIST CAP, but that will vary depending on how the distributor is installed wont it?


Thanks

 

Yes it will. the distributors orientation is really determined by the vac cannistor since it needs room. If mechanical tach drive- limited even more. You pop it in and the rotor points where it will. Rotating the distributor is really rotating the cap in relation to the rotor. Rotating #1 spark plugs turn on the "merry go round"

The rotor always points to #1 cylinder (short hand for #1 spark plug wire. Engines come in varing flavours which place the distributor at front or back or reverse the banks even for odd. Its spark to cylinder not the physical cylinder location.

BTW you don't have to use #1 but any cylinder can be chosen. All your doing is getting the distributor in the general area of when the spark has to be fired... end of the compression stroke/beginning of the power stroke, which means both valves closed. If you guessed and guessed wrong then #1 is swapped 180* and then go from there.
That would be the end of the exhaust stroke/beginning of the intake. 180* out of phase.

 

Although I started the thread down stream a little on timing, I may as well jump in here too.

On my 70 L-46, the orientation of the distributor is more toward the #2 or 4 cylinder. That's with the original distributor. It's true that the vacuum can and more so, the tach connection will limit that. As stated thats not all that important.

If you have the AIM for your year, you will see that GM tell you the orientation off a centerline down the engine. There is also a stake mark on the distributor collar at the base and a matching stake mark on the block where the distributor gasket sits.(toward the rear). When installed they will line up. Thats what GM set as the best orientation for clearances. (Not always so).

 

So in reality that is true, with engine at TDC, when dist drops in rotor needs to point towards front left of engine towards the #1 spark plug.

I couldn't figure out some of the papers when they talked about rotor pointing to #1 on the cap. I know Lars paper goes into finding TDC when you cannot rely on the damper, if you think it has slipped.

When I always tried to find TDC, I would pull #1 plug and know it was close when the air comes out, and then double check where 0 on damper was and where the rotor was pointing.

I guess that is all still correct.

 

you can have it point anywhere you want...the third cylinder back number 5 is usually where the rotor points on an HEI system...but like we said you can make number 1 cap postion on the dist cap be anywhere you want to, and there are two different positions used for most SBC

 

Bob,

I'm usually not this dense, but when you say you can use any spot on cap as #1, you mean you just start at any spot for #1 and feed wires in clockwise order for the firing order correct? On non HEI systems doesn't #1 start at the left of the dwell door thing.

 

With the distributor body held in just one location- as if it was going to be dropped in- you can turn this rotor any which a way and it ain't going to matter except for the oil pump tang, which can be turned to match.

You can insert it one tooth at a time until you've gone all the way around. If you MUST have a specific cap tower be #1 then just set it up that way. But because of the helical gear, one tooth too short, it will rotate correct.

What your probably thinking of is the actual wire lengths and where they run. If the stock set up requires #1 tower to be basicly towards the front then being at the back might screw this up. Pretty sure it isn't #1 that is the problem but one of the others near the firewall that switch funny on the fire order/engine location. You could also do this to make #1 be a specific landmark on the engine or vac advance so you can take them all off and still know which is 1.

 

This pertains to HEI, but may help clear some things up:





just look at my picture above. That is a view of the distributor from above. The front of the car is labeled, and you can see the orientation of the wire pack on the HEI distributor.
so, find your number one tower, then go down to where the cap meets the body of the distributor. Draw a line on the distributor body right under the terminal of the #1 terminal. Then when you have the cap off and are installing the distributor you want the rotor to point to that line when you have the distributor fully seated in the engine and the engine is set to top dead center. Know that when you are installing the distributor the rotor will turn as it goes into the engine, so you need to set the rotor ahead a little. If you did it right, the rotor will line up with #1 when installed.


HEI distributor correctly installed in car, front of car on left, viewed from drivers side. Note #1 terminal.



Under the #1 terminal make a mark on the distributor body. See black mark on distributor body, under the #1 terminal.
Now remove the cap.


Start installing distributor body in engine. Note that rotor is not pointing at the mark for number 1 on the body, but is turned pointing more at the fender. That is because as the distributor drops into the engine and the gear engages the cam gear, the rotor will turn. The objective is to have the rotor point to the mark for #1 when the distributor is FULLY SEATED.

As such.



If the distributor will not full seat in the engine it is most likely because the oil pump shaft slot is not lining up with the notch at the end of the distributor shaft gear. You will have to take the distributor back out and with a very long flat screwdriver turn the oil pump shaft. You need to turn it so when the distributor drops in the engine fully it lines up with the inside of the distributor shaft gear. This takes some practice.

If all is seated well the rotor should be pointing very close to the #1 mark when fully seated. If you have the crank set at 0 degrees timing it should point right at it. If you want to set your static timing, turn the crank to about 8 degrees before top dead center and then turn the distributor body so the mark lines up with the rotor. You will then be able to secure the distributor, install the cap, wires and fire it up. Time with a timing light after that.

Hope this helps.

 

and pictures too....good job

 

Most execelent, the pictiures are great, thanks

 

If you're running an HEI, the #1 cylinder position in the distributor cap is the forward tower on the driver's side with the distributor installed "square" in the block (electrical connector directly on the driver's side). Thus the rotor effectively points towards the physical location of the #1 cylinder. However, on a points-type system, the #1 tower is the forward passenger side tower, and the rotor does not point toward the physical location of #1 cylinder. With the distributor in the stock orientation (vacuum advance control unit pointing 45-degrees forward on the passenger side), this makes the #1 tower the locaton between the dwell adjust window in the cap and the vacuum advance unit. If you install the distributor in the recommended Service Bulletin orientation with the vacuum advance pointing 90 degrees straight out towards the passenger side, the #1 tower becomes the location right at the window.