Topic: Tech Tip - Distributor teardown and modification
Well I finally went ahead and pulled apart the distributor to make some internal adjustments. While it was apart, it seemed a good idea to clean things up and get the various parts working smoothly instead of their previous gunky and stiff movement. Make sure you rotate the engine so the distributor rotor is pointing to spark plug number one before you pull the distributor out, and just remove the bolt that holds the distributor clamp to the engine and pull the clamp out with the distributor. Since there is no guide in the service manuals, I had to wing it for most of the way. If anyone wants a list of the dissassembly steps, let me know.
Cleaning up and lubricating the internal parts really freed things up and made the distributor much more stable in operation. Prior to this, you could see the timing mark moving around when using a timing light. Afterwards, the ignition timing was steady and the timing mark appears stationary when setting the timing. The vacuum advance no longer has to fight friction from crud and can operate smoothly. Same for the mechanical advance. This makes a difference in how the ignition advance comes in, and now it can actually be called an advance curve instead of an advance lurch.
Now, my motivation for doing all this is a problem with getting the best ignition timing for both city and highway driving. If you do an old-school power timing, then you get great drivablility for around town with good throttle response and torque for manuvering in local traffic. Unfortunately, when you add up the initial ignition advance, plus the vacuum advance, plus the mechanical advance, you have over advanced timing for highway driving. To fix that, you back off timing a few degrees to get good throttle response and the ability to cruise with little throttle on the freeway. That, of course, takes away the low speed driving benefits and you get sluggish peformance around town.
With the distributor apart and the mechanical advance exposed, I adjusted the stops that limit mechanical advance to reduce the total advance at high RPM. The results turned out very well and I'm able to run 14degrees BTDC initial advance at idle, the mechanical advance comes in smoothly, and the vacuum advance is there when cruising with a light throttle. The car is a joy to drive now in both in rush hour traffic, AND the hammer lane.
Leaving the distributor clamp attached and using that for the vice to hold onto worked out well, especially if you have a swivel vice.
Removing the breaker plate exposes the mechanical advance.
This is the shaft with the mechanical advance. Note that the two weights are setup so that one reaches full advance early (between 1500 and 2300 RPM depending on model), and the other one does not reach full advance until about 3800RPM (depending on distributor and age). The mechanical advance comes in gradually as the RPM's increase, unless the mechanism is dry and crusty like mine was 
A little cleaning can't hurt!
This roller and spring cup keeps even pressure on the breaker plates. It can be remove by gently prying the clip off the retainer pin on the back side. With the clip off, rotate the plates so the tab on the other side lines up with the notch, then you can separate the two plates for cleaning. Don't break the ground wire!
I used a small brush to coat the bearing and other sliding surfaces with oil (synthetic of course, lol)
For re-installing the breaker plate, I lowered it into place, then used a screwdriver the rotate it partially into position.
To lock the breaker plate into its final position position, I used needle nose pliers with tape to prevent marking the cam surface. Note that the pliers contact the flat part of the cam instead of the lobe... just in case!
Make sure you have the collar in the correct position before installing the retaining pin. The two tabs are offset. It will be correct when the rotor position is pointing to where plug wire number one will be, and the tabs are offset towards the back of the car. Tap the drive collar retainer pin in a little to get started, then press in using a vice. If you don't have a vice, then you will just have to tap it all the way in. If you have a big vice with gnarly teeth, then use something to protect the distributor. The vice can not drive the pin all the way in, so a couple more taps with a drift or other suitable tool are needed to position it correctly anyway. The collar is loose by design, but the pin should not protrude on either side when the collar is pushed the other way.
Reassemble the remaining parts, and you are ready to throw it back in the car!
Paul
Last edited by Altema (2010-07-13 14:31:03)
