DWS964

What would be the impact of the distributor being installed with the primary shaft gear off by one tooth? In my pre-Porsche days, on my "antiques", they would likely not run at all.
Since having my distributor belt replaced this summer, amongst the rest of the tune up, I have not been "satisfied" with the performance - I expected more improvement after fixing the broken belt. I recently experimented by disconnecting one of the igniters - the car ran OK; I disconnected the other igniter, the car ran, but sputtered a bit especially at speed. (but, I don't remember which, primary or secondary)
Today, after finishing my oil change, I decided to pull the caps, and check to see if the secondary rotor was possibly off by a tooth or two on the belt. But what I found is that the two rotors are aligned correctly (per the #1 marks on each housing), but the entire distributor is apparently off by 1 tooth (1/12). It is timed 1/12 (30deg) early (the rotors point to #1 before reaching TDC mark on pulley )
So, the question is - does it make sense that the engine would run (and not too badly) with the distributor off by one tooth? I wanted to check this out before I pulled it out.
(oh, and the hold down nut was missing, too. I am going to have a long talk with the shop that did the work.)

DWS964

The distributor(s) are primarily just mechanical operation for directing the spark to the correct plug(s), so I can see how the engine might run (especially since the rotors are advanced). But, I would think this offset of the distributor shaft would result in an erroneous signal from the hall sensor that is used to identify TDC#1.
I'm still confused why the car runs as well as it does. It ain't broke (completelly), so I''m not going to Fix it, until someone helps me with some answers.

jsacrey

If it's too far advanced, couldn't this lead to premature detonation before the piston gets to the top of the stroke? I wouldn't take the chance man...It's not tough to get the distributor out, just align the engine on TDC (Z1 on the pulley and the main distributor rotor on the alignment mark) and then give it a hearty pull to get it out after removing the nut. I initially had to use a prybar to pop the seal on the old o-ring, but then it pulled right out with my hands.

After getting it out, move the rotors back about 1/4 to 1/2 inch to the left of the alignment marks and re-insert it back into the block. Check your timing marks to make sure everything is aligned and you'll be good-to-go. If not, then redo it again and move a bit farther back to the left of the timing marks and try again. DO NOT MOVE THE CRANKSHAFT until you get everything aligned and back in place!

DAVISRILEY

Darell, anytime this weekend coming up if you want to take a run up, you are more than welcome to compare anything on mine to see if there is a difference. As far as I know I don't have anything going on.

Geoffrey

The orientation of the distributor does not have anything to do with ignition timing on the 964. Ignition timing is controlled by the ECU only.

springer3

Correct, but one tooth on the gear is a large angle. I wonder if your problems are not related to the rotor pointing between two spark plug wire terminals. I would not drive the car again until I was sure the rotor was pointing dead center at the correct terminal. You could be randomly firing the wrong plug, and that risks engine damage.

Geoffrey

It may also cause carbon tracking on the distributor cap and you'll want to check that. If you have some, replace the caps.

DWS964

I agree that the distributor "timing" has nothing to do with the ignition timing - that is all done by the crank sensor and the DME The 964 distributor just mechanically "distributes" the spark. With the dist off by 1 tooth, the rotor points right between two posts at TDC. (2 teeth and it would send the spark to the wrong plug)
The caps are new, at the time of the dist belt replacement, but they do look to have a bit more tracking at the posts than I would have thought for being relatively new.The way it is set up now, the spark is having to jump an extra distance to the post, even when the ignition timing is running advanced.
I still wonder about the impact on the hall sensor (which all the reference material says that it is used in the knock sensor logic and operation).
Anyway, I will pull the dist out today and slide it over a tooth. Looks like I will have to do a bit of prying, it would not pull out with my hands.

DWS964

This evening I pulled the distributor up, turned the shaft back - CCW - one tooth, and reinstalled. With the TDC mark lined up on the crank pulley, both rotors were now pointing at the #1 marks on the distributor bodies.
The car would not start - only sputter and popped back.
I am very confused. I pulled it out again, put it up a tooth (with the rotors turned 30deg (1/12) past the #1 marks), and it started just fine. This is a case of it aint broke so don't fix it, but something is wrong here - either the car or me. This should not be so hard.
Of course, I forgot to take pics before I buttoned it up - to prove that I am not on drugs. I need to take a look at a good one - I will go check out Dave's car when I can.

Darrell

springer3

There is a helix on the distributor gear - it does rotate as you slide the unit in. I assume you are checking after the distributor is all the way in. Possibly you are using the wrong timing mark - there are three on the pulley, and the cylinders associated with each mark are on compression dead center and intersection dead center. Make sure the timing mark is the one for #1 cylinder, and make sure # 1 cylinder is on compression stroke. If both rotors are pointing at #1 spark plug wire with the piston at compression TDC, you are good to go.

I have no clue why it would run fine one tooth off. I have timed many distributors on cars and boats, and not seen this problem. I have forgotten to install the rotor during the final rush to button up and start the engine. That no-start mystery is solved the instant you pulled the cap to check on things.

Geoffrey

It may be 180 degrees out.

f@tboy

Hi Darrell, the interesting words in your OP are "...amongst the rest of the tune-up". Are you sure it isnt a bad plug, plug cap, or something else?

DWS964

Yes, that is my next path (once I get this misalignment-of-timing-marks-even-though-the-engine-runs issue out of my head). I want to check the coils (the car came with a set of non-oem MSD-Blaster coils installed), individual plugs (new plugs) , caps and rotors (new), and leads (new set of wires). To reiterate, the engine runs good; the issue is that I did not feel an improvement after the dist belt repair and tune up.
The "tune up" included a new clutch, DMF, crank sensor, valve adj, all the might-as-well's.
Thanks for all the help.

Lorenfb

"I agree that the distributor "timing" has nothing to do with the ignition timing - that is all done by the crank sensor and the DME The 964 distributor just mechanically "distributes" the spark. With the dist off by 1 tooth, the rotor points right between two posts at TDC. (2 teeth and it would send the spark to the wrong plug)"

That was the most correct analysis, i.e. the rotor MUST be oriented correctly
as the timing is advanced with RPMs or the spark will eventually jump to the
wrong cylinder. Thus, having the rotor off by one tooth will potentially cause
a missfire as the timing is advanced. This is an inherent potential problem
with an electronic timing combined with a mechanical distributor. Even a bad
rotor, where one section of the tip is bad can cause poor starting or a misfire.

The Hall sensor only controls sequential injection and determines cylinder ID
for unique (to each cylinder) knock control (w/o it all cylinders have same retard).
Actually, the Motronic really didn't need a Hall sensor for knock control,
since all that is needed is a reference timing point which can be "stored"
as the knock occurs..

dfinnegan

Do you have a pic?
Are these the notches that you are lining up with?
(N.B. this pic is turned 180 degrees from the installed postion)