Camshaft timing is a popular subject among engine builders and enthusiasts alike. It is an area of great debate due to the effect of changing the valve events in relation to crankshaft rotation on performance. If camshaft timing is such a critical aspect of performance, then timing control during operation is equally important. However, maintaining control is not discussed as often as it should be.
Comp Cams put together a tech tip video to get the conversation moving forward. The video covers the top three methods for controlling camshaft timing, and provides some insight as to when each option is appropriate.
Timing chains are the most popular method of controlling camshaft timing, especially in American V8 engines. There are two types of chains: link belts and roller chains. Link belts are made of metal links pinned together to form a chain. The chain links slide over sprockets with teeth mounted to both the crankshaft and camshaft. Roller chains are made of pins and axles forming a captive bearing between the links, allowing the chain to spin freely.
Pitfalls of the link belt include heat generation and frictional drag. They are a good option for daily drivers due to their low cost and general availability. However, heat and drag are not desirable in performance applications. Unless you are refreshing your daily grocery-getter, upgrading to a roller chain is a wise investment.
Roller chains are of the same type as bicycle or go-kart chains. The captive bearing rolls across teeth on the sprockets significantly reducing drag in comparison to the link belt. Rollers are available in both single and double designs. Double roller chains are essentially two single chains side-by-side. For most street upgrades and performance applications, the double roller design is recommended.
The second type of design is a gear drive. This design uses gears to drive the camshaft in lieu of a chain. As with chains, gears have a couple different styles, namely the dog bone and idler styles. The dog bone style has a center set of gears that ride between the top and lower gear while the idler style is one gear that is mounted in position.
Gear drives are noisy. In fact, that is the reason some choose the gear drive. They create a whine like a roots style supercharger. The engine block may need to be modified and a special front cover installed which may interfere with front accessories. Crankshaft harmonics are also transferred to the valvetrain by the gear drive. However, the rigid construction keeps timing intact even at high RPM.
Belt drives are the third type of timing control covered in Comp’s video. Belt drives are mostly used in high end racing applications like NASCAR and Pro Stock. Two styles are used. One is a tension fit and the other uses an idler pulley. Tension fit systems have been tuned for belt resonance.
Like the gear drive, belt drives may require block machining to fit. Cost is also a major factor. Prices over $1,000 are common. However, they are very precise and accurate. As a result belts are an excellent choice for racing applications.
The top three methods for controlling timing are chains, gear drives, and belt drives. Chains are best suited for daily drivers, upgraded street, and mild performance engines. A double roller chain is most common. Gear drives are very noisy and transfer harmonics into the camshaft and valvetrain, but their rigid construction makes them great for consistent timing control. Belt drives are very expensive, yet very accurate – making them best suited for the racetrack only.