I am considering changing the distributor on my 84 with a performance DUI unit? Is that a simple job? How do you assure that the new one is lined up properly on the gear?

 

remove the distributor cap, mark a point on the engine or some other stationary object the the rotor is pointing at. remove the old distributor and install the new one so that the rotor will be pointing at the same mark. Do not bump or turn over the engine with the distributor removed. Make sure the new distributor is fully seated on the oil pump shaft. The distributor ring should sit flush with the top of the intake if the two sharft are correctly engaged.

 

Those who have done it before find it simple, but for a first-timer, well that's another story.

At a casual glance it seems simple, but if do a search you'll finds lots and lots of posts from guys who haven't been able to fire their engines after replacing the distributor.

There are actually two things that must be aligned properly; the rotor tip and the distributor shaft/oil pump drive. Getting those two in the proper position/index is the key.

Here's what I'd do.

After removing the distributor cap, I'd mark the location that the rotor tip is pointing. When you install the new distributor it's rotor tip must point at the exact same spot, so this is crucial for a quick fire up.

MAKE SURE THE ENGINE IS NOT TURNED OVER/BUMPED WHILE THE DISTRIBUTOR IS OUT OR A WHOLE DIFFERENT PROCEDURE HAS TO BE USED TO INSTALL THE NEW DISTRIBUTOR.

Next is the indexing of the distributor shaft with the oil pump drive rod.

When you remove the old distributor, the distributor gear will turn. It has to otherwise you wouldn't be able to remove the distributor. This also turns the oil pump drive rod.

Now, when you go to install the new distributor, with the rotor tip pointed at the exact spot you marked, the distributor will not drop all the way down onto the intake manifold.

Why?

Because the slot in the oil pump drive rod is not correctly positioned to index with the distributor.

So if you move the distributor gear so that it indexes with the oil pump drive, then the rotor tip will not be pointed in the correct direction.

What to do?

There are basically two ways to get them both in the correct position.

One is to drop in the new distributor with the rotor pointed correctly, then use the starter to bump the engine over. As you bump the engine, the distributor rotor will turn (and thus the distributor gear AND the distributor's shaft/oil pump drive), but the oil pump will NOT turn (since it isn't indexed with the distributor). As you bump over the engine, at some point the distributor and oil pump drive will properly index (align with each other) and the distributor will drop all the way down onto the intake manifold.

Since the distributor and camshaft gears were meshed when you began the bumping, the rotor position will continue to be correct, assuming you pointed it in the exact same position as the old distributor had been in. The timing will need to be tweaked once the engine is running though.

The OTHER way is to use a long screwdriver. Remove the distributor, insert the secrewdriver into the distributor hole all the way down until the tip of the screwdriver indexes with the oil pump drive. Turn the screwdriver (and thus the oil pump drive), then re-install the distributor and see if the drives index while AT THE SAME TIME the rotor tip is in the correct (marked) position.

If not, pull the distributor, again, screwdriver, turn, re-install, check. You'll have to keep doing this unti; BOTH the oil pump driver and the rotor tip are correctly indexed/positioned.

The way to tell in which direction the oil pump drive needs to be turned, look at the very underside of the distributor; look through the bottom of the hole in the gear. You'll see the drive tang. That is what fit in the slot of the oil pump drive. So the oil pump drive rod needs to be turned so that when the distributor is dropped in with the rotor properly positioned, the tang will drop into the oil pump slot.

It'll probably take several attempts to get them both correctly positioned using this technique. Bumping's a lot easier.

Hope this helps.

Jake

 

which way is advancing the timing & which one retarding? is it different on different years or same gm thing? also how much each way is how many degrees?


[Modified by dand1892, 7:55 AM 5/22/2004]

 

I would bring Nr. 1 cyl. to TDC, then pull distributor. If the car was running fine before the pull, then the rotor should already be pointing at Nr. 1 tower on the distr. cap.
When you pull the distributor, note that the rotor will turn about 45 degrees CCW as you look down on it. When you are ready to install the distr., lineup the rotor to this position(45 CCW), then lower the distr. into the block. You will note that the rotor will then turn CW to point to the Nr. 1 position.
This will only work if you did not turn the engine while the distr. was out.
Like the comments before, its a different ballgame if you did.

 

A quick two cents. First, Jake has outlined the project, very well. I have had my distributor out more times in the last month than I care to discuss. See "Good Help Is Hard To Find". Briefly, I found that by inserting a screwdriver into the oil pump driveshaft slot and turning it about a 1/32nd of a turn (not much at all) CCW, the distributor will drop back in, the first time. Besides noting where the rotor is pointing, before you remove the distributor, note where it is pointing as it just clears the cam gear (when it quits turning). This will insure getting started on the right tooth the first time, and engaging the oil pump driveshaft on the reinstall.

RACE ON!!!

 

On Chevys, turning the distributor body CCW advances the spark timing.

Generally, 2 degrees at the distributor equals 4 degrees at the crank. That applies for each way.

RACE ON!!!