Joseph R. Demers
Z Car Tips and Tricks IZCC #4072
 
JRDemers' Homepage
 
 
IZCC #4072
       
Distributor Rebuild
    What started as a bit of play in the distributor shaft of my '79 ZX has become me making and selling distributor bushings. The details about the bushings and purchasing them are on another page and I would suggest reading through the rebuild very carefully before purchasing them. I will concentrate on rebuilding what I feel was the best of the distributors, the D4K8 and D6K8 series for the 280ZX models 79-83 (more information on these is available at Jason's page). Why are these the best? Because, they have a solid state ignition module that is attached directly to the distributor housing making it extremely easy to put into earlier model Z's. I actually rebuilt one of these to go into my 70 240Z and replace the point unit distributor. It is an easy exchange and one which will be discussed in this page. While the ignition module changed during the course of evolution, the distributor body remained the same and I have rebuilt distributors from 83's and simply put an earlier model ignition unit on them. A very good discusion about the merits of the different distributors is Jason's Dizzy FAQ.

Regardless, I assume you found this page because you feel that your distributor needs some work.


Removing the distributor:

    A nice thing about the Z's is that the distributor drive shaft is asymmetric. You can simply remove the distributor and not have to worry about putting it back in and lining up a gear. However, if you want to practice good automotive repair habits: turn the crankshaft to TDC and see if the rotor is lined up with the #1 sparkplug wire on the cap (remove the cap and see if that is where it is). If not, turn the crankshaft one more time to TDC (it turns twice for one rotation of the distributor) and now it should be lined up. You should already have the cap off, so go ahead and remove the vacuum advance hose and the ignition module connector. Remove the two 10 mm bolts at the base of the adapter where it connects to the timing chain cover. There you go, that was easy.

Checking the distributor:

    I often get emails about the ignition module failing (on the side of the Dizzy). This failure is usually very easy to diagnose. You could be driving along just fine and then the car quits - Tach drops immediately to zero. It usually occurs after the car has warmed up or gotten hot. After you let the car cool for a few minutes it starts up again without a problem as if nothing happened, then it does it again...Because a number of Z heads feel that the ignition modules are outrageously expensive, they have developed a way to use a much cheaper GM ignition module with earlier model distributors. Not of interest to me but maybe to you.

    Before discussing the rebuild, it is worth deciding if your distributor needs rebuilding! Even if you just replace an ignition module, it is worth making sure the rest of the distributor is working properly. Usually distributor problems come on gradually and are characterized by poor idle, or poor gas mileage. Sometimes you can put a timing light on each spark plug wire and see a miss occasionally. Poor gas mileage can also be attributed to a failing vacuum advance system. This can fail in two ways. First, the vacuum dashpot may have a hole in it. This is easy enough to check, just get a piece of hose, attach it and try to suck air through it. Second, the breaker plate which the vacuum dashpot turns falls apart and the ball bearings it rides on fall out of place. It gets stuck, and no more advance.

    You can actually check the distributor shaft for play before removing it, but I like to check it out of the vehicle. First, the shaft should turn freely. You might feel the reluctor points as they pass the stator points (see image), but they should not touch the stator points. Further, they should all have about the same clearance. You might find that contact has already broken or worn a couple of the stator points. Wiggle the distributor shaft and see if you can get the reluctor and the stator to make contact. If so, the bushings are shot. Some people have also reported the bushings "screaming" or clearly making noise. This might be solved by simply rebuilding the distributor and greasing the existing bushings.

Rebuilding the distributor:

  • Remove the cap and rotor - straight forward.
  • Remove ignition unit - it should already be marked with red/green. Use needle nose pliers to remove connectors.
  • Remove the 3 bolts holding the stator in place If the reluctor does not come off easily, then remove this before trying to pry off the reluctor! If you do not, you may damage it! It should come off easily, but sometimes the pickup coil sticks to it. Don't break the magnet!
  • Here is a picture of the stator (not a good one unfortunately). It has a magnet behind it - if the magnet is cracked or broken, then, in my opinion, it needs replacement.
  • Now, with the stator out of the way, you can pry the reluctor off. Without the stator out of the way, prying the reluctor off always results in a broken stator
  • Remove pickup coil, and check that it has ~ Ohms resistance.
  • Remove screw from vacuum advance to breaker plate. Then remove vacuum advance dashpot.
  • Remove the two screws holding in the breaker plate. Don't worry about direction, you can check it from the image.
  • Remove breaker plate. Note if the ball bearing cage on the breaker plate has broken and the ball bearings have come loose. The breaker plate should rotate freely back and forth.
Returning to the exterior of the distributor:
  • Remove bottom adapter: first note or mark with a scribe the position on the adjustment plate.
  • Remove adjustment plate: scribe top on the top. This is necessary if you are going to bead blast and paint it. I put dents in the top.
  • Remove the collar by pushing out the roll (spring) pin. This is a cheap item, just plan on replacing it.
    The shaft is now free to be removed, but check it for play and rotation now that the junk is off. You might have to clean the end of the shaft that the collar was on with a 3M scotch pad (not steel wool, it is a green nonmetallic dish pad) before it will slide out of the distributor housing. There is one washer between the housing and the collar and three thin washers between the shaft assembly and the inner flanged bearing (see image). Sometimes the flange breaks and it appears that you have four washers in the distributor - one which is rather thick...

    If you decide to remove the governor weights etc., be warned that upon reassembly, you can get the rotor and the shaft 180 degrees out of alignment. When reassembled, the short side of the alignment slot in the bottom is on the same side as the rotor contact (see picture - ok, it isn't a great picture, but it could save you some trouble).

    Clean up the shaft with the 3M scotch pad and some soap and water (or solvent if you like) and visually inspect it for damage. Make sure you clean out the oil groves at the bottom. Here is an image of a nice clean distributor shaft. Even the oil grooves at the bottom have been cleaned. If the top of the shaft were the reluctor attaches was rusted, clean this up with sand paper or a file, then oil it. This is when you decide to replace the bushings or not. Clean it, and then grease it with a little molybdenum grease and return it to the housing. How much play is there? Does it freely rotate? I just pulled a distributor off of an '83 280ZX that had 110,000 miles on it and the distributor bushings were fine. A little wear is normal, but deep grooves could prevent the bushings from working effectively.

Ok, now if you decide that the bushings need to be replaced,

I strongly advise getting a distributor from the junkyard and rebuilding that one!

    Or having a back up plan in-case the bushings will not press in or there are un-forseen difficulties because removing the old bushings will destroy them - there is no going back! So far only about 1/3rd of the bushing replacement attempts I have made have been succesful! Now that you have a distributor from the junkyard, check it as above, and see if it needs to be re-built. No surprise if it does. It has probably seen more or equal mileage as yours. Go ahead and clean it up and see if it needs to have the bushings replaced. Of the two distributors that you now have, replace the bushings of the one which is in the worst condition. Mix and match shafts if necessary to get a nice, woblle free distributor. Try the replacement bushings on the shaft. There may be a little bit of play, but once they are pressed in, this will disappear.

Time to remove the old bushings. I use a nut driver and a hammer (click on image for larger image).
 

    This step, however, will destroy the old bushings, so make sure that you do need to replace them! Knock the bottom one out, flip the unit over and knock out the flanged one. Before going further, see if the new bushings fit. Actually, they shouldn't. They should be just barely too large to fit. If they slide in easily then there is a problem and you should contact me. After checking the bushings, I solvent clean the whole distributor, then seal up the interior with rags and masking tape, cover machined areas with tape, and bead blast it. Aluminum will oxidize so it is necessary to seal it after bead blasting. I use a product called Steel Wheels (one of my favorite products) which holds up well and I like the color (see rebuilt).

    After you have cleaned up the distributor it is time to install the new bushings. Using the back of a hammer, gently tap the bushing in. For the bottom bushing, it may be necessary to put the distributor on a block to prevent bending the cap hold downs (image below click for full size image).

Now that the bushings are in place, put some molybdenum grease on the clean distributor shaft, and the 3 washers that go between the flanged bushing and the shaft (see image), and slide it into the housing. It will be a little difficult, but once it is in all the way and the bushings lined up with where the old bushings were, it should turn very smoothly! Check it at this point, it should turn smoothly and have no side to side play....

Now it is time to start putting it together.

  • Clean and regrease the ball bearings on the breaker slide if you didn't replace it.
  • Return the breaker plate with the cap locator in the right position as well as the hole for the vacuum advance pot.
  • Install vacuum advance dashpot, and test that a vacuum rotates the breaker plate.
  • Check to make sure the shaft turns easily: if not find out where it is hanging up.
    Through-out the rebuild process make sure that the shaft turns freely and doesn't rub. For some reason one of the problems I encounter is that the replacment bushings "cock" the shaft at a slight angle. Why this occurs I do not understand but may be do to the manufacturing process with the original bushings...
  • Install pick-up coil and then stator, but don't tighten down yet (again check that it is rotating freely).
  • The reluctor may need to be tapped on (use an oversized socket) with the shoulder in the up position. Make sure the roll pin is in place.
  • Now rotate the shaft and see if there is contact between the reluctor and stator. You haven't tightened down the stator yet because you want to align it so that the gaps all the way around, while rotating remain the same. Tighten the stator down firmly, but don't over tighten, you may break the magnet.
  • Attach the ignition unit and wires.
  • Now, I usually add the collar last so that I can check for rotation throughout the whole re-assembly. At this point grease the bottom of the distributor, add the washer and the collar. Tap the roll pin into place.
  • Put the adapter plate and foot back on adjusting so that it is in the same orientation as before. You should have labeled the positions to make this easier...
  • Return it to the auto.
And there you have it! I would suggest either replacing the wires and plugs before doing this (making sure the car runs after your work) or after this, but not at the same time. If you just work on one item at a time if the car doesn't work, you only have to trouble shoot one item....Hopefully your car will run much more smoothly after this operation.
 

Swapping into an earlier Z:

    I hate adjusting points! When I found out that I could put an electronic ignition in my 1970 240Z I jumped at the opportunity! When I found out that it was only a two wire swap, I was estatic.

    First, turn the crankshaft to TDC and see if the rotor is lined up with the #1 sparkplug wire on the cap (remove the cap and see if that is where it is). If not, turn the crankshaft one more time to TDC (it turns twice for one rotation of the distributor) and now it should be lined up. Then, disconnect the ground terminal at the battery, the wire running to the distributor and, finally, remove the original distributor (special note, remove the distributor with its respective adapter plate, that is, remove the complete distributor from the timing chain cover). Now, put your D4K8 distributor in palce and wire her up! Here are schematics (much thanks to Dick Denno):
 
 

Original Wiring (click image to view)
Modified Wiring (click image to view)

Note: these are currently lousy pictures - I will improve them in the future!

    If you can read schematics, then there you have it! If not, then what you need to do is take the wire that was originally going to your points (from the minus pole of the coil) and connect it to the C connection on the outside of the ignition module. Then run a second wire from the B terminal on the ignition module to the plus connection of the coil. The connection to the balast resistor from the coil should allready be there. Now, just short out the balast resistor. I left mine in place and simply ran a wire between the two connectors.