'It seems pretty simple, one shaft turning another, and with gears, chains, or belts, there are a variety of devices for getting the job done. We're talking about the camshaft, and there are a variety of cam-drive systems available for most popular engine applications. The factory setup favored in most engines is the familiar three-piece timing-chain set, a system that provides long life and reliable service, so why change it? There are other questions to answer as well, so we had a look at the four commonly available types of drives to pin down their advantages and disadvantages. The we ran 'em on a 440 Mopar to see which made the most power.
Competition Cams Adjustable Timing SetHow It Works: It's a conventional three-piece chain.How It Goes On: Like a stocker.What We Like: It's simple to install, the timing can be changed without removing the chain, and it's cost effective.What We Don't: Timing chains can stretch over time, creating slack in the drive. The setup can be loose in line-bored or -honed blocks, which can be a problem in applications where undersize chains are not available. The timing cover usually must be removed for cam timing adjustment, though a timing cover with a separate cam access plate bridges this hurdle.Noise: You'll never know it's there.PN/Price: 3125 KT, $206.65 (summitracing.com)Source: Competition Cams; Memphis, TN; 800/ 999-0853; compcams.com
Milodon Fixed-Idler geardriveHow It Works: A fixed-idler geardrive mechanically links the crank and cam with a trio of straight-cut gears, with a drivegear on the crank, a driven gear on the cam, and an idler gear in between to link them together. A simple two-gear drive will spin the camshaft backward, so the idler gear is there to change the direction of rotation.
How It Goes On: The cam and crank gears install much like a standard timing set, the key installation requirement being the placement of the idler gear to set the lash. With the full timing cover style, the case is aligned to set the lash between the three gears and then doweled so it always goes on and off in exactly the same place to maintain the proper lash. The "cheater" style has the idler mounted on a steel plate, which likewise needs to be positioned exactly to set the lash. Depending on the application, some drilling or tapping of the block is required, but this can be done with common handtools.
What We Like: The cam timing can be changed easily and accurately once you become familiar with the way it works. We also like that the cam can be accessed for handy cam changes. The bottom line is the three-gear fixed-idler system provides a rock-solid and unwavering connection between the crank and camshaft. The bonus is the trick look of the specialty cast-aluminum timing cover.
What We Don't: Requires a water-pump spacer for clearance in some applications, which can complicate accessory-belt installation.
Noise: Audible straight-cut gear whine, most noticeable at idle. However, the noise level is pretty subdued; not at all obnoxious.
PN/Price: 13000, $469.95 (summitracing.com)
Source: Milodon; Simi Valley, CA; 805/577-5950; milodon.com
CAT Dual-Idler geardriveHow It Works: Dual-idler geardrives differ from the fixed-idlers because they have intermediate gears floating between the cam and crank gears. Tie-bars between the two idler gears set them at a fixed distance from each other, and when placed on either side of the cam and crank gears, the dual-idler gears become captive. It seems like kind of a questionable arrangement, but the design has been around for decades and has proven itself in service.
How It Goes On: A dual-idler geardrive installs under the stock timing cover. Essentially, the cam and crank gears are installed in position and then the idler gears are slipped in between. Double check for lash, fore and aft alignment, and clearance.
...
>>next page