The distributor gear is one of the smallest components in the engine, but also one of the most important. Spark timing is driven off of the distributor gear, and in most cases the oil pump is driven by it as well. The distributor gear is located at the bottom of the distributor shaft and engages with a gear on the camshaft. Selection of the proper distributor gear for your cam application is crucial to optimum engine performance and longevity.
The four most common types of distributor gears are composite, bronze, cast iron and melonized steel. Composite distributor gears are manufactured from a super-strong polymer that both increases durability and is the lightest in weight. COMP Cams® Composite Distributor Gears are tested and available in several shaft diameters for popular street and race applications. Meanwhile, bronze distributor gears are made from extruded aluminum
bronze with 5 percent nickel added. These gears conform well to the mating camshaft and will not damage the cam gear. They also feature a strong tooth design that resists wear. Next, cast iron gears are developed in a manner which solidifies the outer layer, while leaving the core molten iron. Since cast iron contains two percent carbon, these gears work well with cam gears made from the same material. Finally, melonized steel distributor gears are most often used in mass production by original equipment manufacturers. Steel is the hardest of all the distributor gears and designed for the longer life of a mild factory engine.
Correctly matching your distributor gear to the type of camshaft in your application is one of the most critical steps when building an engine. Both camshaft type and material affect the type of distributor gear you need. Selecting the improper gear can lead to premature gear wear, possible camshaft wear, voiding your camshaft warranty, and ultimately, engine failure.
Cast Iron Gear
Ideally, your distributor gear will be softer than your cam gear. This allows for proper mating and prevents excessive wear on the cam gear. Most cams come with multiple distributor gear options, however, it is of utmost importance to know your cam type prior to making a selection.
Cast iron and composite gears are suited for hydraulic and solid flat tappet cams, while melonized steel and composite gears mesh with austempered ductile iron hydraulic and solid roller cams, or those camshafts that have been nitrided. Finally, either bronze or composite distributor gears are your options if your camshaft is a billet steel hydraulic or solid roller. When used with a steel camshaft, the composite distributor gear has increased durability of 300 percent over a bronze gear.
Whenever possible, COMP Cams® recommends the use of a composite gear, as it conforms well to the mating cam gear and is compatible with any camshaft gear material. These are the most common distributor gear types and pairings, but if you have a unique application or specific concerns, please contact COMP Cams® to make sure you are utilizing the right components.
Improper gear selection can lead to failure
There are several trouble areas that may arise due to improper distributor gear selection. First of all, it is imperative that shimming heights are correct, meaning it is critical for the distributor gear to be centered to mesh properly with the cam gear. If this is not done, a process called “knife-edging” will occur. Next, the use of a high volume oil pump can wreak havoc with all types of distributor gears, due to the increased resistance of rotating these types of oil pumps. Small Block Fords have historically been one of the toughest applications in which to make a gear “live” due to engine oiling design. They also have the smallest distributor gear in the industry, and the oil splash may not be sufficient. Finally, if you are replacing a camshaft, it is also necessary to match it with a new distributor gear. The old gear will be mated to the original camshaft and will not work properly with the new cam application.
This is just an overview of how to select a distributor gear that will match your specific camshaft. COMP Cams® techs will want to know the type of cam application in your vehicle, as well as how the vehicle will be utilized. For assistance in selecting the proper distributor gear, call the COMP Cams® Help Line a 1.800.999.0853 or visit www.compcams.com