Tech: Informative Overview of Timing Chain Design and Application

cloyeslead

Performance parts are readily available for almost any engine combination today. There are parts marketed toward the budget street rod builder and racers alike. One could spend hours looking through catalogs and part warehouses trying to select the components that will provide that balance between performance, reliability, and cost that most are coveting. Determining which part is best for any given application can be daunting.

Timing sets are no different. They are one of the most critical components inside the engine. If the timing chain is the weakest link (pun intended), the engine may not make it further than second gear. On the other hand, overkill on the timing set may break the bank. The aim of this article is to educate the reader on the options available to them, and provide some input from the experts at Cloyes Gear.

Non-Roller Versus Roller Chain

There are two common chain designs used in today’s engines: the link chain and the roller chain. Non-roller chains, or link chains, have stacked rows of flat links connected together via pins. The links are shaped to fit the contour of the teeth on the timing gear or sprocket.

Roller versus Non-Roller chains. The chain on the left is a non-roller. Contoured links contact the teeth on the timing sprockets. A roller chain is shown on the right. Barrel-type rollers roll across the sprocket teeth reducing friction and wear. Note the double row on this roller chain.

Perfect Timing

Timing valve events for optimum performance got a lot easier with the Hex-A-Just gear from Cloyes. In addition to a three-keyway crank sprocket, the cam gear is infinitely adjustable /- 6 degrees from the index point. This allows the builder to hit the desired valve timing perfectly.

While discussing indexing tolerances on timing gears Thompson says, “You will find variable tolerances with regards to different manufacturers. As a general guideline, an installer can expect to be within a 0.25 of a degree from the marked index point of a multi-keyway crank sprocket. As for Hex-A-Just, there is obviously a tolerance but the intended use eliminates the tolerance factor. An installer using a Hex-A-Just with a degree wheel will rotate the infinite adjustable Hex-A-Just bushing to the location that results in the desired angle, not to an index point.”

As the crankshaft rotates, the teeth slide inside the contoured links. As the teeth and links make contact, the chain moves and consequently rotates the camshaft and any other components attached to it. While this type of chain can be inexpensive, it does wear out sooner than the roller-type chain. Sprocket wear will cause variations in timing and increase harmonic vibrations.

As with any metal-on-metal design, rollers offer a reduced-friction solution compared to non-rollers. Cloyes’ True Roller chains feature “cold rolled” and hardened rollers mounted between side plates. This barrel-type roller is mounted around a connecting pin. The rollers make contact with the sprocket teeth. As the sprockets turn, the chain rolls across the sprockets reducing friction, and consequently, wear.

Cloyes’ Aftermarket Director of Product Development, Jason Thompson, says, “We use the advantage of roller chain systems and the inherent friction/wear resistance coupled with Cloyes’ custom tooth profiles to dissipate load spikes and match engine block center distances. The result is a timing set that provides exact cam timing angle with an enduring fatigue life.”

Single Row Versus Double Row

In the roller chain realm, there are two widths available for many applications: a single row and double row. Single row chains have one row of rollers and links connected end-to-end. Double row chains have a second set of links and rollers adjacent to the first set. The additional row of rollers adds an extra layer of durability. While the single row may be suitable for a stock engine, performance applications need to be upgraded to a double row chain.

A single row roller chain.

A single row roller chain.

Upgrading to the double row is recommended when a performance camshaft or other power enhancement is installed. The aggressive lobe profiles of performance camshafts require heavier valve springs in order to maintain control of the valve events.

The additional spring pressure and power increases strain on the timing chain. A double row chain disperses the additional load across both sets of links keeping chain fatigue in check. However, there are design limitations that may require a single row chain to be used in certain applications.

Z-Chain And Its Benefits

The process in which the chain is manufactured also plays a part in strength and longevity. Cloyes Z-Chains offer the utmost in reliability, even for the most extreme engine builds. Boasting 33 percent more strength than the company’s premium chain, the Z-Chain has several unique features that make it the top choice for all-out racing applications.

First, Cloyes uses a proprietary heat-treating process on this particular chain. The process used on the high-strength steel chain is kept under wraps for now. Thompson replied with a short “no” when asked if he was able to elaborate on the unique heat-treating process. Nevertheless, the improved strength is reason enough to trust the engineers at Cloyes know what they’re doing.

Cloyes' Z-Chain features a proprietary heat-treating process.

Cloyes’ Z-Chain features a proprietary heat-treating process.

Second, while not a proprietary Cloyes process, the chain links on the Z-Chain are produced using a process called fine blanking. Fine blanked links maintain high tolerances and excellent flatness. Fully sheared, straight-cut edges all but eliminate stress fractures under load. More on the fine blanking process can be explored here.

Third, the center links on the Z-Chain are press-fit onto the pin. According to Cloyes, press-fitting the center link improves the load share across the parts of the chain, reducing potential increases in load on one single component. This load sharing bolsters the overall strength of the chain.

Z-Chains are available in a single roller design for select engines, like the LS series, and a double roller for other common applications.

“Creating a timing drive system begins by qualifying the center distance between the crankshaft and camshaft.” – Jason Thompson, Cloyes Gear

Center Distance Is Critical To Eliminate Deflection

No matter what type of chain is used in an engine build, there is one measurement that is critical to maintaining consistent valve timing and limiting chain failure. This measurement is referred to as center distance (CD); it’s measured as the distance between the centers of the camshaft and crankshaft.

“Creating a timing drive system begins by qualifying the center distance between the crankshaft and camshaft. The actual center distance from crank to cam may or may not match the theoretical center distance based on chain pitch, number of pitches, and sprocket tooth count,” says Thompson.

(Left) Center distance is shown in this illustration. Qualifying the CD is critical to eliminate deflection. (Right) Premium timing sets are hand-matched and CD is checked in this special fixture.

For this reason Cloyes hand-matches all of its premium timing sets. Trained technicians match sets by analyzing critical fitment features of the components. The set is then placed in a special pneumatic fixture that rotates the timing set under load to qualify the CD of the set is within tolerance. Incorrect center distance will cause deflection in the chain, resulting in timing variances and chain whip. Premature failure of the chain is imminent in this case.

Any boring or honing of the main bores on the block will cause the center distance to shorten. To compensate, Cloyes offers chain sets in -0.005 and -0.010-inches for align-honed blocks. The CD must be measured in order to determine which set will best fit your application.

Overhead Cams And Chain Tensioners

Overhead camshaft engines have a large CD and require the use of tensioners to maintain proper tension on the chain.

“The advent of both SOHC and DOHC engines redefined the means by which structure and tension are maintained within a timing drive system. OHC engines require long center distance systems in many applications, which create more room for failure,” says Thompson.

With the use of a longer chain, tolerances can stack up, causing the actual CD to be quite different than in theory.

Overhead camshaft engines have a long center distance. Multiple chains are used on this Modular Ford engine.

Overhead camshaft engines have a long CD. Multiple chains are used on this modular Ford engine.

“The long center distances require stability through dynamic tensioning in order to maintain chain fatigue. This stability is provided by spring tension, hydraulic tension, and hydraulic dampening provided by a tensioner. Instability causes chain deflection, which results in timing variation and chain whip, both of which lead to failure. So, it is critical that dampening demand is met with dampening/tensioner capacity,” says Thompson.

Pulling the pin on the tensioner. Timing chain tensioners provide dynamic stability for overhead cam applications.

Pulling the pin on the tensioner. Timing chain tensioners provide dynamic stability for overhead cam applications.

Conclusion

Roller chains provide reduced friction and wear over the link chains, offering better performance and longevity in comparison. Upgrading to a double roller chain is a must in performance applications. Dual rollers provide the extra strength that is required for the increased power and valve spring pressures.

For all-out extreme duty engines, Cloyes offers the Z-Chain. This exclusive chain offers a proprietary heat-treating process, fine blanked links, and press-fit center links. The Z-Chain is available in double as well as single roller designs for applications that may not permit the use of a double roller chain.

CD should be measured on align-honed blocks. Cloyes offers shorter CD chains for these applications. By hand-matching timing sets to qualify CD, chain deflection is eliminated, resulting in consistent timing and increased chain life.

For overhead cam applications, CD is longer and requires dynamic tensioning and dampening through the use of chain tensioners. Tensioners should be replaced with the timing set to maintain chain stability.

Article Sources

About the author

Eric Labore

Eric LaBore's extensive background includes a solid education in automotive and high performance motorsports technology and 10 years of working in the industry. Currently, he is a full-time ASE master technician and advanced engine performance specialist. As a former dyno operator and engine assembler, he is passionate about custom and performance engines.
Read My Articles

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