Distributer recurving is necsessary for racing or high performance use,because the OEM curve is to reduce emissions on a stock engine. Most stock ign. timing curves are too wide,and too slow.Narrowing the mechanical advance curve allows you to run more initial timing 8-12 BTDC giving a smoother idle.Changing the advance springs to lighter ones ,quickens the mechanical advance.I sell a spring kit for Mopars that fit most of the late 60s-mid 80s distributers.My spring kit and the following instructions do not apply to oddball distributers Chrysler sometimes used like the cast iron "prestolite",dual point,and the latest MP unit. The first step is to remove the reluctor if your dist. has electronic ignition,skip this step if yours has points,as the breaker cam can't be removed. Some reluctors have two keyways,so mark the one that the rollpin is installed in before removal. It can uselaly be removed by evenly prying up with two screwdrivers as shown.
Next step is to remove the two screws holding the vacuum advance pod. The arm for the pod is sandwiched between the upper and lower advance plate,and inserts in a hole on the upper plate.The upper plate could have two holes,so take note of the location if it does.The upper and lower plate are held together with a spring loaded pin that can't be accessed at this stage,but has enough "give" to alow you to remove the vacuum pod arm by lifting up on the upper plate as shown.
Next,remove the two screws holding the lower advance plate to the distributor housing,and lift out the plate assembly.Often,it will not come out easily,and prying up with a screwdriver inserted in the vacuum pod cutout will help.
If you want to disassemble the lower and upper advance plate for cleaning,push down and slide this clip to remove.This is the spring loaded pin mentioned earlier in this post.
Next step is to remove the snap ring located inside the upper shaft. You'll need a long,thin nosed set of pliers, you might have to grind the pliers thinner. Grab one leg of the snap ring,then pull upward,and spiral the snap ring out of the grove.
Now we're down to the heart of the matter,that awful heavy spring has got to go.
The heavy spring we just eliminated did have a purpose,it was to reduce Nox emissions by not allowing full advance until 4,000+ RPMs.However,the mechanical advance must be reduced on most distributers to prevent pinging at high speed,and allow more initail advance to smooth the idle. This is best done by mig welding and filing the advance slot to a narrower width.Brass brazing or silver soldering is acceptable,but lead soldering or epoxy will not last. I also don't recommend heating and bending the ends of the advance slot.
Using a square file,finish the outsides of the slot to the desired width. I recommend 0.380 for a S/6,0.400 for a smallblock,and 0.410 for a bigblock. Here are slot length to degree info.:
Cam Crank Slot length
6° 12° 0.340"
7° 14° 0.357"
8° 16° 0.375"
9° 18° 0.390"
10° 20° 0.405"
11° 22° 0.420"
12° 24° 0.435"
13° 26° 0.447"
14° 28° 0.460"
15° 30° 0.475"
16° 32° 0.490"
17° 34° 0.505"
18° 36° 0.520"
Re-assembly is just a reversal of the dissassembly,don't forget the spring clip in the upper shaft.
