Wednesday, March 2, 2011

2 Point Mopar Distributor Restoration

The article featured on this page is from the April 2011 issue of Auto Enthusiast Magazine.

A Two-Point restoration



Bringing back a dual-point Mopar distributor

Story Earl Duty

I was at a Mopar event and had opportunity to stumble around the swap meet. During my hike among the offerings of new and used parts, I noticed a number of ignition distributors including the bulletproof cast iron (dual point) unit that became a workhorse for delivering firepower to the V-8 Mopar muscle of the early ’50s, ’60s and ’70s.

Asking prices for these chunks of iron ranged anywhere from $50 to $400 depending on condition and application. During my 40-plus years of automotive repair, I had never seen one of these cast iron distributors go completely bad. They just rusted up due to age and the elements.

My goal was to take one of these rusted old chunks of iron and see what it would take to refurbish it. For my rebuild/restoration I picked out one of the more common distributors. The one I chose is typical of cast iron dual point distributors that came with a vacuum advance. Should you want to rebuild your own distributor, this would at least give you the basics for your particular cast iron dual point application.

Theory of Dual Points

A single set of ignition points operating at a high speed has a very short saturation time (coil voltage build-up) — whereas the dual points of the Chrysler distributor effectively extends this voltage build-up time, producing a much hotter spark at high speeds. The points are connected in parallel and staggered in relation to the 8-lobe cam. This overlapping of the contacts allows for a longer saturation time and no voltage is released until both sets of points are open.

I started the tear down by extracting the old points, and any related wiring. Next I removed the tiny clip that keeps the vacuum advance arm secured to the rotating breaker plate and removed the vacuum advance (don’t lose that tiny clip). After removing the screws that secured the distributor cap hold down clips, the breaker plate could be lifted from the main housing. This left me with one roll pin at the bottom of the mainshaft, which required a punch and small hammer for removal. Caution:safety glasses are required.

With the roll pin out of the retaining collar, I then used a hammer with a hard plastic head to tap the main shaft out the larger opening of the housing. The removal of one final spring clip at the top of the mainshaft allowed me to remove the one-piece cam lobe and the underlying mechanical weights and springs.

Wipe Away The Years

Cleanup of all parts and pieces was next, where I used a combination of media blasting, “Mean Green” (a readily available cleaning solution), and cleaning solvent.

Fortunately, I have a friend who has a glass bead cabinet and the glass bead media used to clean the parts was micro-fine and removed nothing more than the surface rust. If you don’t have a blasting cabinet, a bucket or pan with quality cleaning solvent will work quite well. You can also use a hand-held wire brush (or sandpaper) for scuffing and rust removal on the cast iron housing prior to solvent cleaning and painting. Just be sure to use chemical-resistant gloves and safety glasses when dealing with any cleaning solvent.

I used a fabricated driver with an OD (outside diameter) of 39/64-inch to press the old bushings out through the large end of the distributor housing. The smaller end of that driver was turned down to 15/32-inch so it would fit inside the old bushings. After removal, the old bushings measured; ½ -inch ID, 5/8-inch OD and were one-inch long. The replacement (bronze Oilite) bushings were readily available at my local bearing and bushing supplier and require little to no oiling.

The mainshaft in our project distributor had very minor wear and required clamping the shaft into a lathe and using fine emery cloth (320 grit) for polishing. If a lathe is not an option for your distributor shaft clean-up, clamping the drive end of the shaft into a vise and using fine emery cloth (320 grit) will suffice. Just be sure to rotate the shaft occasionally for uniform cleaning. By the way, there’s a reason the distributor shaft and the bushings wear – it’s because rarely does anyone take the time to oil the bushings via the oil fill tube built into the distributor housing.

The distributor breaker plate cleaned up quite well in the Mean Green solution and by swiveling the bearing retainers off to the side, I was able to treat the old bearing to a fresh coat of a lightweight lubricant called Lubriplate. After the cleanup and repainting of necessary parts, the reassembly was a reverse of disassembly, with the project concluding by setting the new points with a feeler gauge to .017-inch (each set). Here’s a little hindsight on my part: It would have been much easier to install the points and condenser onto the breaker plate while the plate was out of the distributor.

To keep the distributor hold down clips and the vacuum advance from rusting, I used Dupli-Color paint (PN EDSGM435 – Light Gray M), which is as close to a new metal finish as I’ve found. I used Seymour semi-gloss black for the cast iron housing (PN 16-838).



1 Prior to starting the rebuild of your dual point distributor, locate a pictorial breakdown of the unit as seen here.

2 Remove the retaining screws holding the points to the breaker plate and related wiring (the condenser and its hold down screw were missing on our distributor). If for any reason you feel you might not remember where something goes for reassembly, break out the digital camera and photograph the teardown.

3 By extracting the vacuum advance screws and the C-clip attaching the advance arm to the breaker plate, the vacuum advance can be removed.

4 After removal of the distributor cap hold down clip screws and the vacuum advance, insert a screwdriver through the vacated pigtail lead opening and gently pry upward to remove the breaker plate.

5 Removal of the mainshaft roll pin requires the use of a punch and hammer. Safety glasses required!

6 To remove the mainshaft from the distributor housing, grasp the housing and with a hard plastic-head hammer tap the shaft out through the top of the housing.

7 After removal of the mainshaft, note the position of these two thrust washers (arrows) and make sure they’re relocated in the proper order during reassembly.

8 Release the spring clip holding the cam lobe assembly to the mainshaft.

9 Document the position of the advance weights and then remove both of them from the mainshaft, along with their attached springs.

10 The layout of parts and pieces ready for clean up, housing bushing replacement, painting and reassembly.

11 My clean up of the distributor parts were – glass bead blast the cast iron housing, hold down clips, vacuum advance, screws and mainshaft. Note: I did not use sand to blast the surface because sand will remove a certain degree of metal from the surface.

12 By connecting a hand operated vacuum pump to the suction port of the vacuum advance I found that our distributor vacuum advance tested perfect and required little more than a cleanup.

13 A thorough cleaning in Mean Green produced a points breaker plate that was again clean and ready for new points and condenser.

14 I used a caliper to measure the mainshaft and found that the bushing wear areas were approximately one thousandth (undersize) from the mainshaft, which allowed me to simply polish the wear damage.

15 To polish the minor wear damage on the mainshaft I clamped it into the chuck on a lathe and used 320 emery cloth to clean up the wear marks. Caution: rotating machinery parts – keep hands and clothing clear.

16 The old bronze bushings are removed by pressing them from the bottom of the distributor out the top. Our new Oilite bushings would be reinstalled in reverse order. Oilite bushings are oil-impregnated bronze requiring little or no external oiling.

17 These original distributor bushings measured 5/8-inch OD, ½-inch ID and one inch long. New replacements made of bronze Oilite material were on the shelf where we get our bushings. Also shown is the fabricated tool used to press the old bushings out and to reinstall the new ones.

18 To cut the oil slot in the upper bushing I simply pressed the new bushing on the end of a length of ½-inch wooden dowel rod. Then with a magic marker I marked the ¼-inch slot on the new bushing and cut it out with a band saw.

19 The new bushings are reinstalled into the housing with the lower being pressed into the bottom of the distributor and the upper inserted into the top of the distributor, making sure the oil slot lined up with the oil fill tube. The upper bushing is pressed just slightly below the lip of the housing allowing room for the thrust washer bevel.

20 Use a small pair of pliers to swivel the bearing retainers on the breaker plate for removal and lubrication of the breaker plate bearing.

21 After lubricating the breaker plate bearing with a lightweight lubricant like Lubriplate, the two parts are ready for reassembly.

22 With new bushings in the painted distributor housing, use a dial indicator to check for play between the distributor shaft and new bushings. Factory specs call for no more than .005-inch. Shaft movement caused the dial indicator to read .002-inch, which was well within specs so no reaming of the new bushings was required.

23 If our distributor shaft had been very tight in the new bushings, an adjustable bushing reamer such as this would have been used. This type of reamer is inserted into a new bushing and by making quarter turn adjustments (at the threaded end) adequate material can be removed from a new bushing allowing for freedom of shaft movement.

24 By following a reverse of disassembly and setting the new points to .017-inch (each set), our refurbished distributor is now ready to resume its intended purpose of sparking a Mopar engine back to life.

2 comments:

  1. yep,the old Prestolite Dist.,where did you find the cap and rotor,?? no one stocks them no more and the dist.is only correct on hemi AND 440 WITH 4 speed

    ReplyDelete
  2. and 340 six-pak,maybe 340 MT too!

    ReplyDelete