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This tech tip/FAQ reveals a technique to repair a loose distributor HEP pulse ring. A loose pulse ring can contribute to a very poor idle quality, surging on acceleration, reduced gas mileage, and in extreme conditions engine stalling.
The loose pulse ring condition is VERY common on high mileage distributors and is caused by the design that uses melted plastic “rivets” or welds to attach the metal pulse ring to the plastic rotator base. The plastic welds weaken over time and mileage and allows the metal pulse ring to wiggle loosely on the plastic rotator base, This undesired movement causes the engine control unit to constantly vary engine timing and injector pulse event and that is what causes the poor drive ability symptoms.
Figure 1
Illustration of loose plastic welds on pulse ring
The cure for this problem is to either replace the distributor with a new one, or to stabilize the pulse ring. To stabilize the pulse ring and avoid the purchase of a new unit, we have discovered that it is easy and economical to install locking screws in the base of the pulse ring.
TOOLS NEEDED
- (2) 4-40 Phillips screws, shallow head, short approximately 3/16” length
- 4-40 High carbon steel plug tap
- 9/64 drill bit
- Red locktite
- Electric drill
- JB Weld (optional step)
STEPS
- Clean the interior of the distributor housing very well, remove all traces of lubricant and debris
- Place distributor in a suitable clamp or vice to hold it firmly for the following operations
- Confirm that the metal pulse ring is properly centered over the plastic rotator base BEFORE you drill the first hole. This is an important step.
- Drill 2 9/64” holes 180* opposite each other in the metal pulse ring plate. Place the hole drilled between any plastic weld and the open hole next to it. (see pictures)
- Using the 4-40 tap, tap threads into the pulse ring plate. Use caution to not allow the tap to run too deep and touch the distributor housing.
6. After tapping in the two 4-40 holes, install two 4-40 Phillips head screws that have been coated with red locktite. You need to use a screw with a shallow as possible head to avoid any contact with the bottom of the HEP. Shown were common pan head screws and there were no clearance issues.
OPTIONAL STEP
At this point you have actually fixed the problem and no further repairs are actually required. For an added level of strength and prevention, it is suggested that you can place a thin layer of JB Weld high strength and high temp automotive epoxy into the pulse ring base. The base has a slight lip on it so it is easily possible to fill the base slightly with JBWeld and simply push it out to the edges. You do not want your JB to be any higher than the screw head(s) or contact with the bottom of the HEP is possible.
If you add the JB Weld, it’s best to allow the repair to cure 24-48 hours prior to placing the distributor back in service. |
