C2 Timing-Can't rotate the distributor

[John Lokay]

Re: C2 Timing-Can't rotate the distributor

Is it safe to assume that if your vacuum can is pointing in the 1 or 2 o'clock position and nothing is in the way(ie. intake manifold, ignition shielding) when moving the distributor to adjust timing that the distributor itself is correctly positioned in the engine?

[Mike McKown]

Re: Check Your Math

Okay. You're right. Using your numbers and not being real precise it's 28 degrees per tooth. A half tooth is worth 13 1/2 degrees. But this means that you have to "adjust" or turn the distributor for 28 degrees at the crank. If my thinking is correct, this would probably cause you to bottom out on rotational travel of the distributor against the manifold runner or the shield and there would be no way to properly set timing within factory specs.

I just wonder if this is affecting some other people.

Mike

[John H.]

Re: Check Your Math

"Bubba" is everywhere - the dimple on the gear is designed to point in the same direction as the rotor tip, although none of the Service or Overhaul Manuals bother to mention it (I think the Delco manuals do). You'd be amazed how many cars are out there with distributors mis-installed (a tooth or two off), and how many of those have the wires re-indexed in the cap towers to compensate for it so the timing can be set. It only takes a few minutes to verify correct distributor installation and plug wire indexing. I learned many years ago not to "assume" that the first wire outboard of the adjustment window is always the #1 wire (on other people's cars).

[Werner R.]

Re: C2 Timing-Can't rotate the distributor

well, all of the above sounds pretty good, including the math. if the dimple is correct and if the can is hitting the firewall [which i guess would happen if you advance things alot] then just move all of the wires one terminal clockwise as alredy described REMEMBERING TO RE-ALIGN THE NEW NUMBER ONE POSTION WITH THE ROTOR WHICH IS STILL POINTED AT THE OLD NUMBER ONE. this will rotate the distributor 1/8 of 360 and move the can away from the firewall. let's see:
1/8 of 360 = pi[pqs] x speed of light with a correction for harmonic subvibration.... oh well, you get the idea.

[Duke W.]

Re: C2 Timing-Can't rotate the distributor

There is only ONE WAY to correctly assemble and install the distributor. The dimple on the drive gear MUST point in the same direction as the rotor tip, and there is only ONE CORRECT POSITION on the cap for the #1 plug wire, and ONE POSITION, that the distributor can be installed on the car and both get the initial timing dialed to spec AND have the distributor rotor properly oriented to the distributor termimals.

Get ANY ONE of these requirements screwed up and you're going to have problems - absolutely, positively guaranteed (as Joe would say)!!!

The trouble usually starts by installing the drive gear 180 out. Then Bubba "fixes" this by moving the wires on the cap.

If you have problems setting you initial timing before the vacuum can hits the manifold do the followiing.

1. Set the engine at the initial timing point for #1.

2. Remove the dist. and verify that the dimple in the drive gear points in the same direction as the rotor.

3. Verify that the #1 plug wire is installed on the proper cap terminal (see your service manusl) and the rest are in firing order in the clockwise direction.

4. Install the dist. and rotate it until the points just begin to open, then back off until they just close, and verify that the rotor is pointing at #1 dist. terminal. This should get you within a few degrees of the proper initial timing.

5. Start the engine and set the timing with a light. Be sure to disconnect the vacuum advance and be sure engine speed is low enough that you are SURE the centrifugal advance has NOT started.

Duke

[Everett Ogilvie]

There Is Only One Reason...

that you can't turn your distributor enough to get proper timing (IF the dimple on the drive gear is correct) - the rotor is off by one tooth, or even more.

There is ONE proper setup - the factory setup. Start by checking to see if your wires are in the correct factory terminal configuration - for a midyear, number one wire is on the terminal between the window and the vacuum can (Shark cars are NOT the same).

I just had to correct all of this on a midyear - the distributor body was in about the "right" position, but the number one wire was off two terminal positions on the cap. I knew instantly that the rotor was off and that some genius had compensated by moving the wires. If you have to juggle wires to compensate for incorrect dist installation -well, this is just sloppy work.

1) Turn the engine so the balancer mark is near zero on the timing tab,
2) Pull the distributor, after noting whether the rotor is "close" to number one or number six,
3) Position the distributor BODY in the factory correct position, as you start to lower the dist into place,
4) As you lower it, back off the rotor position CCW a bit such that when you fully drop the distributor, the rotor then points very near one or six (previously noted),
5) You can "feel" the correct rotor tooth, by moving the rotor back and forth as you start to seat the dist, to get an idea of which is the correct fully seated position - you may have to reposition the oil pump drive to line it up so that the dist does drop all the way down,
6) Once you know the dist body is in the correct initial position, and the rotor is on the right tooth, put on the cap and index the wires on the ONE proper terminal connection, determined by the factory.

Done. Time it. It will time, because the factory installed the dist this way leaving enough room to turn the dist. body to advance or retard within a considerable window. It won't hit anything. If it does, you are still off a tooth on the rotor. (Or, the balancer HAS slipped, which is really bad... as stated here before).

On most engines, there are also factory stake marks on the distributor/intake showing where the factory located the distributor. You can use these, unless your distributor or intake are no longer matched due to replacement of either or both components.

[Werner R.]

Re: C2 Timing-Can't rotate the distributor

the duke is, as always, correct. if everything, including the balancer and dimple, is correct, and if your can is hitting somthing, then you have to move your wires as necessary to gain clearance. very easy to do.

[Mike McKown]

All Very Good Information

Evryone knows by now that I can't do fourth grade math, at least on the first try. I guess I have another problem. Can't seem to get my point across. One last time, I'll re-state the question which has yet to be answered: "What negative effects will I see (SPECIFICALLY) if I install a distributor in my c2 Corvette that has had the distributor gear installed 180 degrees off"?

All the responses so far have assumed that the gear is either correct or someone has compensated by moving wires on the cap, re-indexing the cam/ distributor gears etc., etc. I thought Duke was going to get it right but he got sidetracked on Bubba. PLEASE ASSUME THE GEAR IS INCORRECT!

The answer is not all that important to me. I can put a Chevy engine together blind folded and set the timing the same way if I had to. I was just thinking of these other guys out there that write in and complain that they can't set their timing without crashing the manifold or the distributor cover no matter where the wires are indexed to or what notch you put the distributor in on the cam.

John is correct as far as I know. It mentions nothing in engine overhaul manuals about this. I knew it was a one way deal years ago and forgot about it until it was brought up twice here lately and made me think about it and my own personal situation.

Can anyone answer my question SPECIFICALLY? If I don't get an answer, I'll either put a gun to my head or I will go swap the gear around to see what happens.

Regards,
Mike

[Clem Z.]

Re: All Very Good Information

mike there are chevy engines out there running with the gear 180 degrees out,i have found this to be true in non corvette applications because after market gears sometimes do not have this dimple. when this happens you have to check the location of the pin hole vs the gear teeth. you may not be able to get the distributor located so you can use the corvette ignition shields

[Mike McKown]

I think we have a winner!

Clem:

This is the answer I was looking for.

So then, it stands to reason, if your distributor gear was indexed wrong on the shaft, whether it be aftermarket or not, you would have the same condition.

This is what I was thinking of about these other people asking for assistance on setting their timing.

With the gear set wrong would you agree with:

1) Your vacuum can would collide with the ignition shield and your timing

would tend to be fast.

2) Or, your vaccuum can would be against the intake runner and the timing

would tend to be slow.

3) No sweet spot in between.

Regards.
Mike

[Clem Z.]

Re: I think we have a winner!

i thought that is what i said now i wished i had taken that writing course in school.

[Duke W.]

Re: C2 Timing-Can't rotate the distributor

I think you missed the point, Werner. Moving the wires is what Bubba does and then lives with the consequences - misfiring and poor power and fuel economy because the rotor tip is not lined up with the cap terminals, so there are lots of misfires due to spark energy being dissipated in the large gap it has to bridge from the rotor tip to the cap terminal. As I thought I stated clearly in my previous post, there is only ONE CORRECT location for the wires - as indicated in the service manuals. If you have to "move" the wires from the proper position to get the ignition timed properly, then something else is wrong.

The point is to fix the ROOT CAUSE of the problem, which is often incorrect installation of the distributor drive gear, not implement a bunch of Bubba-inspired bandaids that will, at best, result in marginally poor engine operation.

Duke

[Duke W.]

Re: All Very Good Information

SPECIFICALLY, the rotor tip will be misaligned with the corresponding cap terminal when the points open. The excess gap will dissipate ignition energy and result in low energy at the plug, which will cause misfires, some so subtle you can barely feel them, but the engine will perform poorly - rough, down on power, and fuel consumption will be very high.

Duke

[Werner R.]

Re: All Very Good Information

duke, mike and clem, i hope that i have mis-understood some of the things said above. clem is absolutely correct that if the distributor drive gear is "turned" 180 degrees, then NO MATTER WHAT, the spark cannot be correctly co-ordinated to fire at the correct valve positon. cannot be done. even bubba cannot do it. never, no how. you will always be about 27 crank degrees off, because if you "rotate" the drive gear 180 degrees, you now have a peak instead of a valley lining up with the cam gear, and you will have to rotate the distributor shaft, either way, until the distributor gear lines up with the cam gear again, and the whole thing drops down. this will create a built in error of spark to valve of 13.5 [distance from peak to valley] distributor degrees [27 crank degrees]. now, there is nothing you can do to get rid of this error except to rotate the distributor drive gear back 180 degrees to the "correct" position. also, i have no idea why GM chose to put and odd number of teeth onto the drive gear. maybe someone does know. may have to do with wear pattern.
finally, to duke, it absolutely does not matter in which terminal the number one wire sits AS LONG AS THE ROTOR POINTS TO THAT TERMINAL WHEN THE NUMBER ONE CYLINDER IS CALLING FOR A SPARK. period. if you don't believe me then try a simple experiment: take off rotor; use remote starter to move rotor to the number one terminal position with engine at TDC; at that point the number one cylinder is calling for spark [forget about ignition advance for a second]. now, pull wires. then loosen hold down clamp. rotate the distributor housing [not shaft, obviously] one termninal "counter-clockwise". then replace all of the wires, in sequence, one wire clock-wise from their original position. you will see that the number one wire is again correctly sitting opposite the rotor tip. however, the entire body [not shaft] of the distributor has been moved [as has vacuum can relative to firewall]. engine will run great. now, if this is wrong, tell me where. i have done it several times without problem when one of the ignition wires was a little too short etc. duke, maybe i just mis-understood what you were saying. as always, thanks for the stimulating advice.

[John Lokay]

Re: All Very Good Information

Werner, great post. In my situation I have noticed that my #1 wire is off one terminal position to the left of where it should be when compared to the original factory set-up. For example, the factory calls for the #1 wire to be located in the terminal post just to the right of the distributor cap window where in my situation the #8 wire is in this spot then followed counter clockwise by the #1 wire. If I understand you correctly, as long as the rotor tip is pointing at the #1 wire in the distributor cap (no matter where the #1 wire is positioned in the cap) at the same time the #1 cylinder is in the correct position for firing, then this is okay and engine performance will not be negatively impacted? If this is true then I can just my existing set-up alone?