Selecting the correct distributor gear is critical for the performance and longevity of your engine. This important gear is located toward the base of the distributor shaft and engages a gear on the camshaft. Engine oil lubricates the gear mesh and resistance is created as the distributor shaft turns both the rotor and oil pump. An improper mesh between the camshaft gear and distributor gear can damage the camshaft, cause inconsistent engine timing and potentially result in a catastrophic event damaging the engine.
Ideally, your distributor gear should be softer than your cam gear. This allows for proper mating and prevents excessive wear on the cam gear. It is extremely important to know your cam type and material prior to selecting a distributor gear. This can be an Iron Flat Tappet Cam, an Austempered Ductile Iron Roller Cam or a Billet Steel Roller Cam.
There are several different distributor gear options; Iron, Steel, Bronze and the newer high-tech Composite. These gears typically come in .467, .500 and .531 distributor shaft diameters and use a 1/8" spiral roll pin. Proper distributor gear selection is dependent upon the material that your cam is constructed from.
Iron Distributor Gear
Hydraulic and Solid Flat Tappet Cams are generally made from cast iron having two percent carbon. An iron distributor gear of the same hardness will work well with these camshafts where a hardened steel distributor gear will damage the softer camshaft.
Steel Distributor Gear
Austempered Ductile Iron Roller Cams are heat treated to create a much harder material having better tensile and elongation properties. The steel distributor gear is also very hard and designed for long life of a factory engine.
Bronze Distributor Gear
Billet Steel Roller Camshafts are turned from a round steel bar and will normally be nitrided after grinding. These are very expensive and usually used only in high performance race engines. The bronze distributor gear is much softer which conforms well to the camshaft and will not damage the camshaft gear. This distributor gear generally requires enhanced oiling modifications to reduce rapid wear and requires replacement one or more times per race season.
Composite Distributor Gear
These are new state-of-the-art Carbon Ultra-Poly Composite Gears created to eliminate performance problems such as gear wear, camshaft compatibility and inconsistent timing due to backlash. Composite gears are made from proprietary space-age materials and are suitable for all camshaft applications including race or street. Immediate benefits are no break-in requirements or special oiling modifications. They are more pliable, long wearing and tend to come slightly oversized creating a good mesh with the camshaft gear. The cost of this technology is about $110.00. Consider it good insurance for your expensive performance engine.
Caution: At the same time that many are touting success, others are warning that a Composite Distributor Gear should not be used with a wet sump oil pump, especially a HV oil pump. The distributor also turns the wet sump drive shaft adding substantial resistance and stress to the plastic gear teeth, where the dry sump only turns the distributor. The good news is if any gear teeth shear, they will likely end up in your oil pan causing minimal engine damage.
In summary, the Small Block Ford Windsor engine is inherently problematic due to the narrowness of the distributor gear facings and oiling design. Distributor gear wear is amplified by the increased resistance of tight tolerances and especially high volume oil pumps found in performance engines. In addition, distributor seat shim height is also critical in order for the distributor gear to be centered for a proper mesh with the camshaft gear. If the distributor gear is too high, knife-edging of the helical gear teeth may occur creating even more backlash, damage to the camshaft gear and ultimately catastrophic engine damage.
- Anytime you replace your camshaft, also replace your distributor gear. The old gear will have a set wear pattern mated to the old camshaft.
- Always use an arbor press when removing/installing a distributor gear to avoid damage of the gear teeth, shaft bushing or distributor shaft base.
- Always use a new roll pin for secondary protection. The Ford distributor gear is attached to the shaft by tight fitting friction, not the 1/8” spiral roll pin.
- Always use camshaft break-in lubricant on the distributor gear for protection until the engine oil circulates.
- Check your gear mesh by applying white grease to the helical gear teeth, installing the distributor and rotating the engine one revolution. If the pattern is not centered in the middle of the gear teeth, the distributor seat may be shimmed to raise the height of the gear for a better center.
- If your distributor gear is set correctly and you still have uneven gear wear, you may have "camshaft runout" or movement. This must be addressed to provide proper gear mesh and longevity.
Comp Cams lists several Common Distributor Gear Problem Areas
- Make Sure The Distributor Is Properly Shimmed. Must deliver the correct meshing or wear pattern between the Distributor Gear and Cam Gear.
- The Use Of High Volume Oil Pumps. Produce much higher gear wear due to increased resistance.
- Small Block Fords Due To Engine Oiling Design. Historically more difficult for the Distributor Gear to live in.
- Not Installing a New Distributor Gear Each Time A New Camshaft Is Installed. New Camshafts require a new Distributor Gear for proper mating and endurance.