Small-Block Chevy Timing Chain And Gears
Article by Mark Trotta
As an engine gets older, a timing chain will wear and stretch, which affects valve timing and hurts performance. Aside from replacing the chain and possibly gears, alternatives would be a gear-drive or belt-drive system.
Stock Timing Chain and Gears
On Gen-One small block Chevy's, most factory camshaft sprockets are light-duty. Some are part-steel with nylon-faced teeth.
The stock Chevy timing chain and gears are fine for light-duty driving, but for any kind of performance they won't hold up. Unless you're building a 100 point restoration, replace your old cam gear and crank gear with all-steel gears.
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Double-Roller Timing Chain
For mild street performance applications, a double-roller timing chain will provide a much longer life and more accuracy than a stock chain.
Cloyes SBC Timing Chain Kit
All of the first-gen small-block's that I've built were street-driven, mild performance engines, and all had Cloyes timing chains and gears installed.
The Cloyes True Roller 9-3100 kit features solid bushing rollers that really roll. The pitch diameter is larger than stock, making it less prone to stretch.
The Cloyes cam sprocket is cast iron and dynamically balanced to 5,000 rpm. That equates to 10,000 rpm engine speed.
There are three keyway slots in the Cloyes 9-3100 crank sprocket. This allows you to set the timing either 4° advanced, 4° retarded, or factory standard (I've always kept them at the standard setting).
Shop: Cloyes 9-3100 Original True Roller Set
Up to around 7,000 rpm, a double-roller timing chain and steel gears are really all you need for good street performance. If you're building a motor to rev more than that, chains will have a tendency to jump gears, which alters timing and can damage parts (pushrods, valves, etc).
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Gear Drive
If you're building a serious high-RPM small-block, consider a gear drive set-up. They can't stretch or wear out like timing chains do. Being solid metal gears with teeth, there is no variation or play. This gives precise timing throughout the RPM range.
Gear Drive Kit
Competition Cams makes a gear drive kit designed to fit small-blocks originally equipped with hydraulic flat-tappet camshafts. The cam and crank gears are made from heat-treated billet steel.
Shop: Gear Drive for Small Block Chevy
Gear Drive Whine
Personally, I like the sound of a gear drive. A friend of mine had one on his small-block Chevelle. At idle, it made a distinctive "whine" that many people mistook for a blower. At cruising speeds it wasn't that noticeable, but was quite pronounced when accelerating!
Gear Drive Issues And Complaints
Running metal to metal, gear to gear drive units transfer harmonics to the valvetrain, whereas timing chains help absorb these harmonics. In very extreme cases, these have led to valve-train parts breakage.
NOTE: Some gear drive systems require modification to a stock timing cover for clearance.
On newer, computer-controlled small-blocks, the harshness of a gear-drive tends to trigger the knock sensor. The computer then compensates by retarding the timing, which decreases the power output of the engine.
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Belt-Drive
In several ways, a belt-drive is the ultimate way to turn a camshaft. A belt transmits very little, if any, crankshaft harmonics. Because a belt is connecting the crank pulley and camshaft pulley, there is no harmonic vibration transfer that you can get with a timing chain or gear drive.
Installing a belt drive system also make cam swaps much easier, and camshaft timing changes are easily made without removing the timing cover.
Shop: Belt Drive System for Small Block Chevy
Belt drives have two big negatives; they're expensive, and they're difficult to install.
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Best Choice For Street-Driven Car
A double-roller timing chain with steel gears is really all you need for a street-driven car. Beyond that, it's all about style and attitude.
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SBC Chevy Timing Chain Cover
In the 40+ years the first-gen small-block Chevy was produced, there have been several styles of timing chain covers. The important difference is where the timing pointer mounts.
Before you buy a Chinese-made chrome timing chain cover to put on your American hot rod, consider re-using the stock piece. The quality of metal is better, and the chrome plating on that cheap tin will hold in engine heat.
Read: Spray Paint Engine Block And Parts
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SBC Timing Pointer
If you decide to use an aftermarket timing cover, it may not have a timing pointer on it. Many suppliers offer a bolt-on timing tab; two bolts attach them to the timing cover. However, care must be taken that it's the right one for your engine and harmonic balancer.
Check that the timing mark on the harmonic balancer is in the right place. Unless the mark is moved to correspond with the new tab, you'll never set the timing correctly.
Larger 8" harmonic balancers have the timing pointer higher up to clear the bigger balancer.
NOTE: Timing chain cover bolts require only 7 to 9 lb/ft of torque, no more.
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Break-In Oil
Lucas 10631 SAE 30 is a high-zinc break-in oil used for flat tappet camshaft break-in. No moly supplement or additional additives are needed with this oil. Not recommended for passenger cars with catalytic-equipped emissions controls.
Shop: High Zinc Break-In Oil
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Classic Car Engine Oil
The 10W-30 oil your car left the factory with is not the same 10W-30 that you buy today. There are more flat-tappet hydraulic cam failures than ever before, brought about by inferior foreign lifters as well as the removal of ZDDP additives from motor oils.
Read: Best Oil for Gen One SBC
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Related Articles:
Timing Chain Installation
Camshaft Selection Guide
SBC Camshaft Installation
Best Engine Assembly Lube
Best Heads For Gen-1 Small-Block Chevy
SBC Valvetrain Assembly
