Distributor reinstallation....timing

[Chris H.]

I checked the timing of the 396 and it was retarded. I can only advance the timing so far before the vacuum can runs into the sheilding....the old "off-a-tooth" syndrome.

My question is during reinstallation of the distributor, which way do I want the new orientation of the rotor tip to go? Move (rotate) towards the passenger side, or the other direction, towards the driver side?

Thanks, Chris

[Duke W.]

Re: Distributor reinstallation....timing

I'm not familiar enough with the details of the L-78 to give you specifics, but you better pull the dist. and make sure the dimple in the drive gear is pointing toward the rotor tip, just like it must be in SBs, even though no service manual that I know of says ANYTHING about this requirement.

Install the drive gear 180 out and you can't achieve the initial timing before before you reach the limit of rotational freedom, no matter how it's indexed on installation.

Also check that the wires are properly indexed on the cap.

My understanding is that there was no service supplement released in '65 for L-78, but the '66 big block service information should probably help.

Duke

[Joe R.]

Re: Distributor reinstallation....timing

Hi Chris:

I have the same problem on my small block, except that I can just barely achieve the desired timing before the vacuum can hits the coil. I pulled the distributor and confirmed that the dimple is in the wrong place. I won't be attempting the fix for a while, but I think it is possible to reason through things and derive the answer that we both need (which direction to increment the rotor).

To advance the timing you rotate the distributor clockwise. If you want to reduce the amount of clockwise distributor rotation needed to get a given amount of advance, you want to move the rotor counter-clockwise. So, I think the steps would be as follows:

1) Note the current orientation of the rotor.
2) Remove the distributor and rotate the drive gear 180 degrees.
3) Reinstall the distributor with the rotor moved slightly counterclockwise from the position it was in at step 1.

I believe the drive gear has 13 teeth, and the resulting counterclockwise increment you are seeking will be 1/2 tooth, or about 14 degrees. By my calculations that translates to moving the tip of the rotor about 3/8 inch counterclockwise.

Note that your oil pump shaft will have to be rotated a similar amount counterclockwise to allow the distributor to drop into place.

Please note that the above is only a theoretical derivation, and I have not yet attempted this on my engine. If my reasoning is wrong I hope some other list members will correct me.

[Duke W.]

Re: Distributor reinstallation....timing

Why won't you be implementing the fix for a while? All you have to do is tap out the roll pin with a drift, rotate the gear 180 degrees, tap the pin back in and reinstall the dist.

On a C2 SB with about 10 degrees initial timing the vacuum can should be about halfway between the interference points at the coil bracket and inlet manifold, and the cap window plane should be close to perpendicular to engine centerline.

If not, something's not right. Proper installation orientation and plug wire indexing is in the appropriate service manuals.

Don't know the specifics for BB distributor orientation.

Duke

[Joe R.]

Re: Distributor reinstallation....timing

Hi Duke:

I won't be implementing the fix for a while because my engine still has some parts removed. I am reassembling it with new intake gaskets, fuel pump, and carb. With any luck, that work might be completed this weekend.

I had planned to hold off on the distributor fix until I confirmed that the engine still runs well. My (cautious) approach to fixing multiple problems is not to change too many things at one time. Once I confirm that the engine still runs well, it will be a simple task to pull the distributor and fix the drive gear position.

By the way, did I get it backward in my last post when I said that you turn the distributor clockwise to advance the timing? I can't actually recall which way it needs to move. In any event, I think the conclusion that the rotor needs to move counterclockise by 1/2 tooth is correct. In my case, at least, the vacuum can is almost touching the coil bracket when the timing is correct, so I need to move the final set point counterclockwise.

The situation might be the opposite for Chris' big block. Perhaps I should just have said that the rotor needs to move in the direction that he wants the distributor to move.

[John H.]

Re: Distributor reinstallation....timing

You turn the distributor counter-clockwise (as viewed from above) to advance the timing; the rotor turns clockwise.

[Joe R.]

Re: Distributor reinstallation....timing

Hi John:

Yep, I suspected I had it backward. In any event, I think Chris needs to move the rotor in the same direction that he would like to distributor housing to move when the fix is complete. If his problem is the same as mine (distributor rotated too far clockwise to get correct timing), his goal should be to move the rotor counterclockwise.

The smallest incremental movement available to him will be 1/2 tooth if he flips the drive gear 180 degrees, and 1 tooth if he doesn't.