Distributor #1 wire position

[Ervin S.]

I have an issue that I believe maybe created by having the wires to each cylinder incorrectly indexed. Should the distributor cap hold down screw be located between the #1 & 2 cylinder wires or the # 2 & 7?

I have an issue that the distributor cap door to adjust the points dwell is at about 8 o'clock looking from the front (6 o'clock). The ignition shielding has an opening at the 6 o'clock position to allow use of the cap door to adjust the point dwell while running that is now inaccessible.

This is a 1970 454 390 HP with correct distributor. The timing is set to specification, the dwell was set at 30 and now has worn to 36 which is to open and causing rough idle and running. The engine was running strong until recently. The plug wires were installed by a well known restoration shop, but I am concerned they are one index off causing the distributor to be rotated clockwise to get correct timing and resulting in the cap point adjustment door being offset clockwise from the ignition shielding cutout that would allow adjustment while running without removing the shielding.

[Kenneth S.]

Re: Distributor #1 wire position

This picture was in an old article about indexing the distributor. Not sure if it works for your big block.
Ken

[Gene M.]

Re: Distributor #1 wire position

Ervin,
First before you are concern about the cap wires position, you need to have the distributor shaft indexed correctly. Also correct positioning of the vacuum canister is necessary to set advance while clearing the shielding and bracket. I can't say about the c3 but the mid years have the rotor pointing at the #1 cylinder when firing on #1. Position of #1 wire is adjacent next to the window opening,(going on memory).

I seem to recall this is illustrated in the assembly manual.

Some where in Corvette history I recall seeing the positioning changing. Again going on memory.....

[Michael W.]

Re: Distributor #1 wire position

Ervin,

To move all the wires one terminal over would also require either turning the distributor housing 45* or removing the distributor and reindexing the rotor accordingly to maintain correct timing . The first is most likely not possible to accomplish as the vacuum advance canister will no longer clear the intake runners and the tach cable will be bent at an awkward angle. The second solution will put the distributor housing right back where it is now and you'll have gained nothing.

The correct orientation of a C3 BB distributor is with the vacuum advance line exiting just behind the passenger side vertical support for the shielding. If this does not match your installation, the 'cure' is remove the distributor (keeping the same relationship between the rotor and housing) and moving it one tooth in the desired direction. Remember to reposition the oil pump drive shaft also.

Hope this helps more than confuses.

[Duke W.]

Re: Distributor #1 wire position

The best way to verify distributor indexing is to look at the applicable CSM and AIM, which should have diagrams/pictures of proper wire and distributor indexing.

Once you find out and have any doubts, go back to zero.

Set the engine at specified initial timing for #1.

Pull the dist. and verify that the dimple in the drive gear is pointing the same direction as the rotor tip.

Verify that wire indexing is correct and reinstall the dist.

Rotate the housing until the points just begin to open and if the engine plant applied stake marks, they should line up.

Start the engine and verify initial timing.

Duke

[Duke W.]

Re: Distributor #1 wire position

This picture was in an old article about indexing the distributor. Not sure if it works for your big block.
Ken

Your photo is for a C1/C2 small block, not a C3 big block.

The answer is for the OP to look as the CSM and AIM as I previously stated and assemble everything the way GM did originally.

When all else fails - read the instructions!

Duke

[Terry M.]

Re: Distributor #1 wire position

I avoided posting that image from the Chevrolet Service News because Erv specifically asked about a Mark IV engine. As I recall there is a diagram of the distributor orientation in the 1970 AIM in the UPC LS5 or in the UPC U69. I can't remember which and my 1970 AIM is not handy and I don't have a scanner at home anyway.

[Duke W.]

Re: Distributor #1 wire position

The OP is asking about a 70 454/390 HP big block. Why contaminate the thread with C3 small block information?

Duke

[Paul L.]

Re: Distributor #1 wire position

The OP is asking about a 70 454/390 HP big block. Why contaminate the thread with C3 small block information?

Duke

I apologize for trying to be helpful. The post has been deleted.