Today I decided to clean up the original distributor and just put the good vacuum advance canister on the original distributor. I would buy a new vacuum advance canister if I could find one but no one seems to sell just the canister at a reasonable cost.
(update - Standard Motor Products VC187 (approx $20) may work, and I'm assuming it is what comes on remanufactured distributors, but I believe it is designed for a 1970's Mopar B/RB engine)
The mechanical advance plate in the original distributor (below) has a very small "8" stamped into it by the upper slot, meaning it provides 8 degrees of distributor timing advance. Since the distributor turns 1/2 the speed of the engine, an 8-degree plate provides 16 degrees of mechanical engine timing.
The replacement distributor I put in the car two years ago (below) has a 15.5-degree mechanical advance plate, so it was giving me 31 degrees of mechanical timing advance (whoo boy!!). That's too much for my engine's 10:1 compression ratio when static timing is set to the stock 10 degrees BTDC, and I believe a partial cause of my issues with driveability.
Just a little tangent here, but the original distributor shown below is stamped with a part number of 2642248, which equates to a 1966/1967 383 4 barrel engine in a B- or C-body Mopar. The "42 5" stamping after the part number is a date code, which is the 42nd week of 1965, or October 1965. That puts it right in line with when my car was built (November 1965). One other interesting note is the number 52 above and to the right of the part number. That 52 shows up on the build sheet as being the distributor callout for my car. All these numbers point to this distributor being original to my car, which makes it more than 50 years old with 159,000 miles on it. Pretty amazing it still works.
Below is a photo of the "parts" distributor I had been using. Same part number as my original one but it has the number 51 visible above the part number block. The part number is a little light, almost like it has been sandblasted, reconditioned possibly since it had a working vacuum advance canister on it. The date code of "4 6" means it was made in the fourth week (January) of 1966. I don't know what car the 51 distributor may have come from. The only thing I do know is the part number identifies it as a '66/'67 383-4bbl distributor housing. Maybe it is for a C.A.P. car (Cleaner Air Package, i.e. sold in California), but that's just a guess.
On to the cleanup. Below is the breaker points plate. It's interesting to see three wear pads made of what appears to be copper, or copper plated. These days the pads would probably be nylon.
This next photo shows the two plates aligned properly. In the above photo the plates are swiveled apart to show the copper pads.
This is the bottom side of the plates showing a three-finger spring that keeps tension between the two plates.
Below are the two vacuum advance canisters. The one on the left is the original one on the car that doesn't work. The right one is newer. I'm thinking someone bought a rebuilt distributor and the company that rebuilt it put a new vacuum advance on the car.
The interesting thing in these photos is the stampings on the two arms. The left one is 9.5L and the right one is 13L. I take this to mean that the original canister would give a maximum of 9.5 x 2 or 19 degrees of vacuum advance at full vacuum. The newer vacuum canister gives a maximum of 26 degrees of vacuum advance (13 x 2 = 26). I'd sure like to find a working "9.5L" canister but I think I can modify the 13L canister to provide less advance. I think the "L" after the number means it's designed for a "left hand" or counterclockwise distributor rotation, which is what Mopar B and RB engines are (350-361-383-400-413-426-440). Mopar LA small-blocks (273-318-340-360) have a clockwise rotation.
Tada... The distributor is complete. Points set at about 14 thousandths and back into the car it goes.
After getting the distributor back in the car, I ball-parked the distributor timing while the car was warming up. I then set timing based on engine vacuum with a 650 RPM idle, and the car seemed to like about 15 degrees of initial timing. I could go as high as 20 and it still worked fine, but I'm more comfortable with 15 at this point. I may bump it up more later. Mechanical timing with the 16-degree plate gave me 31 degrees of total (static + mechanical) timing at 2500 RPM (not counting vacuum advance, as the car is timed with vacuum advance disconnected).
Initial impression is that the car works much better now. I only took it around the block tonight so at some point I need to do more "in-depth" testing. On a long, lonely road. At night. With no moon....
If anyone is wondering about the vacuum advance giving too much timing advance, it would seem like it. Let's add it all up. Initial static timing advance is 15, mechanical advance is 16, and vacuum advance is 26. That adds up to 57 degrees. Fortunately the engine would only see that 57 degrees in light-load part-throttle operation.
..... and Ported Vacuum:
One more thing about vacuum advance on my car (and a lot of other cars from the '60s). The carburetor on the car is a Carter AFB, and the vacuum advance port is called "ported" or "timed" vacuum, which means that the vacuum port only provides vacuum to the distributor once the throttle plates open. This is because the internal vacuum port is slightly above the throttle plates and all the vacuum is under the throttle plates. When the throttle is opened slightly, the vacuum port "sees" engine vacuum, and the vacuum advance canister then starts applying advance to the distributor. When the gas pedal is pressed further, the throttle plates open further, causing engine vacuum to drop, thus decreasing vacuum advance. At some point during the throttle-opening event, engine vacuum drops to the point vacuum advance goes away and the only timing advance is from the initial static timing and the mechanical advance built into the distributor. So at full-throttle operation, my distributor will be providing 31 degrees of total advance timing to the engine.
Here's a little rant. I occasionally watch car shows like Fast N Loud or similar, and it seems like more often than not, when they try to start a new engine, the timing is so far off that the engine doesn't start or it backfires through the carburetor and a fire ensues. It's not rocket science to get initial timing close enough to get the engine running on the first try. Oh, and get the spark plug wires in the right order and set for the correct rotation. Ok, back to your regularly scheduled programming.
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