Many four-cylinder engines and some V6 engines use one or two balance shafts to cancel the secondary vibration that the crankshaft and pistons create. The shafts spin at twice crankshaft speed in opposite directions, which makes the engine smoother at higher RPM.
How Balance Shafts Are Driven
- Belt drive: a separate balance shaft belt and tensioner, usually serviced with the timing belt.
- Chain drive: a balance shaft chain with its own guides and tensioner.
- Gear drive: balance shaft gears driven directly from the crankshaft.
Common Problems
- A broken balance shaft belt that gets caught in the timing belt.
- Chain or gear noise from worn guides, tensioners or gear teeth.
- Worn balance shaft bearings, which can reduce oil pressure on some engines.
- Increased vibration when the shafts are out of time.
Service Tips
- Align the balance shaft timing marks exactly as the service procedure shows. One tooth off causes noticeable vibration.
- Replace the balance shaft belt and tensioner whenever the timing belt is replaced.
- On chain-driven systems, replace the chain, guides and tensioner together.
- Inspect balance shaft bearings during a rebuild and check oil passages.
Balance Shaft Elimination
Some builders remove balance shafts on certain engines, using an elimination kit to seal the oil passages. This increases vibration and is not appropriate for every application, so confirm it is an accepted practice for the engine before choosing this option.
Evergreen Parts
Evergreen offers balance shaft components identified by engine or vehicle application. Use the Evergreen eCatalog to find the right part, and see where to buy Evergreen through our authorized distributors.
