A balance shaft kit either restores or removes the shafts that cancel an engine’s built-in secondary vibration. A replacement kit renews the parts that drive and time these shafts, typically the belt or chain, tensioner, and guides, so that the engine runs smoothly again. Meanwhile, an elimination kit seals the oil passages that feed the shafts so a builder can take them out, trading smoothness for fewer moving parts.
Most drivers need the first type. The second type belongs mainly in race and high-RPM builds, where vibration matters less than simplicity.
Key Takeaways
- Balance shafts spin at twice the speed of the crankshaft, in opposite directions, to cancel the secondary vibration that the pistons and crankshaft create.
- Replacement kits restore the drive system, while elimination kits seal oil passages so that the shafts can come out.
- Belt-driven systems usually get serviced with the timing belt, while chain-driven systems need the chain, guides, and tensioner replaced together.
- Timing mark alignment has to be exact, since one tooth off can cause noticeable vibration.
- Removing the shafts increases vibration and doesn’t suit every engine or every driver.
Why Engines Need Balance Shafts
Many four-cylinder engines and some V6 engines produce a vibration that crankshaft counterweights can’t cancel on their own. Thus, automakers add one or two balance shafts.
The vibration is because of how the pistons move. In an inline four, two pistons rise while two fall. Because of the connecting rod’s angle, the pistons accelerate harder near the top of the bore than near the bottom, so the forces don’t fully cancel. This leftover force peaks as the pistons change direction, which happens twice per crankshaft revolution.
You’ll feel it as a buzz through the engine mounts, floor, and steering wheel. It also grows quickly as RPM climbs. Larger engines with a long stroke relative to rod length tend to produce more buzz, which is why big four-cylinders like Honda’s H22 use balance shafts.
How an Engine Balance Shaft Cancels Vibration
Each shaft carries an intentionally off-center weight, which creates its own vibration that’s timed to oppose the engine’s.
In twin-shaft designs, the two shafts spin in opposite directions at twice the crankshaft speed. Their side-to-side forces cancel each other out, while their up-and-down forces counter the engine’s secondary vibration. But this only works when the shafts stay in time with the crankshaft.
How Balance Shafts Are Driven
Balance shafts are driven from the crankshaft through one of three setups, which determines what a kit contains.
Belt Drive
A separate balance shaft belt and tensioner turn the shafts. Replacement kits usually include the belt and tensioner, and some add an idler pulley. Shops typically service this belt alongside the timing belt.
Chain Drive
A dedicated chain with its own guides and tensioner drives the shafts. Kits for these systems typically bundle the chain, guides, and tensioner, and some include sprockets.
Gear Drive
Gears driven directly from the crankshaft turn the shafts. These systems rarely need a kit unless the gear teeth wear or a rebuild uncovers damage.
Kit contents vary by engine, so match your vehicle’s year, make, model, and engine code to the listing before you order.
What a Replacement Balance Shaft Kit Does
A replacement kit returns a worn drive to its original timing and tension. This restores smooth operation and protects nearby timing components.
Common Signs You Need One
- Increased vibration: The shafts can fall out of time from a stretched chain or a belt that skipped a tooth.
- Rattling or whining: Worn guides, tensioners, or gear teeth can make chain or gear noise.
- Low oil pressure: Worn balance shaft bearings can reduce oil pressure in some engines.
- Belt wear: Cracks, fraying, or missing teeth are often discovered during a timing belt job.
Why Belt Condition Matters
A broken balance shaft belt can get caught in the timing belt. This can knock the cam timing out, and cause valve damage in an interference engine. To avoid this, replace the balance shaft belt and tensioner every time you replace the timing belt.
If you notice a sudden change in vibration, new rattling from the front of the engine, or an oil pressure warning, pull over safely and have the engine inspected before you keep driving. Catching the problem early can keep it from spreading to the timing system.
Installation Tips for Balance Shaft Kits
Accurate timing is the most important part of the installation. Align the balance shaft timing marks exactly according to the service procedure. Even one tooth off causes noticeable vibration, and you won’t fix it by adjusting anything else.
Replace related parts as a set. For belt systems, this means the belt and tensioner. For chain systems, replace the chain, guides, and tensioner together, since a new chain running on worn guides tends to wear out faster.
During an engine rebuild, inspect the balance shaft bearings and check the oil passages that feed them. After the installation, rotate the engine by hand through a couple of full turns and recheck every mark before starting it.
Procedures vary by manufacturer, so follow the service information for your vehicle’s engine.
What a Balance Shaft Elimination Kit Does
An elimination kit lets you remove the balance shafts by sealing the oil passages that fed them. Without thid step, oil would keep flowing to empty bearing bores, and the engine could lose oil pressure.
The work varies by engine. For some Honda H22 kits, for example, you’ll have to pull the cylinder head, plug the holes that send oil into the balance shaft chamber, and then install a block-off plate.
Why Remove Balance Shafts?
- Less rotating mass: Removing the shafts cuts parasitic drag, which matters most in high-RPM builds.
- Fewer failure points: No balance shaft belt means no risk of that belt fouling the timing belt.
- Weight and appearance: Some vehicle owners want a lighter engine and a cleaner engine bay.
- Race and swap builds: Stiff aftermarket mounts already transmit plenty of vibration, so the comfort loss matters less.
Some owners with belt-driven systems simply remove the balance shaft belt and leave the shafts in place, so that they stop rotating. This skips the oil passage work, but confirm it’s an accepted practice for your vehicle’s specific engine before trying it.
The Trade-Offs
KeeElimination increases vibration. You’ll feel it at idle and cruise through the steering wheel, seat, and mirrors, and the extra shaking can add stress to mounts and accessory brackets over time. Elimination also isn’t appropriate for every engine. Confirm that it’s accepted practice for your ride’s engine before you commit, because reversing it can entail a teardown.
Replacement or Elimination: Which Fits Your Build?
For a daily driver, replacement is the practical choice. It keeps the engine as smooth as the factory intended and maintains the timing system the engine was designed around.
Elimination makes more sense for a dedicated track car or a high-RPM build where comfort comes second. If your car still sees regular street miles, expect a noticeably rougher feel and plan around it.
FAQs
It isn’t a good idea. The engine might still run, but the broken belt can wrap into the timing belt and cause serious engine damage. Shut the engine off and have it inspected before driving further.
The engine develops noticeable vibration, often worst at certain RPM ranges. Recheck the timing marks against the service procedure and correct the alignment.
Many four-cylinder engines and some V6 engines use one or two. Larger four-cylinders, such as Honda’s H22 and GM’s Ecotec family, are common examples. Check your engine’s service information to confirm.
Yes, for most belt-driven systems. The labor overlaps, and replacing both belts and their tensioners together reduces the chance of a failure that damages the timing system.
They can in some engines. Worn bearings let oil escape faster, which can drop pressure. Inspect them during a rebuild and check the related oil passages.
Any gain is small. The main benefits are lower rotating mass and less parasitic drag, which mostly help engines that spend time near redline.
Find the Right Balance Shaft Parts
Whether you’re restoring a smooth-running daily driver or preparing a high-RPM build, the right parts make the job go faster. CarParts.com carries balance shaft components, timing kits, and related engine parts you can filter by year, make, model, and engine. Enter your vehicle’s details to find parts that fit and get the engine running smoothly again.
Keep Reading: Related Posts
Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.
