Timing Belt Kits: Why Buying the Kit Beats Buying the Belt Alone

"Timing belt" and "timing belt kit" are often used interchangeably, but in workshop practice they’re very different decisions. A belt alone leaves the old tensioner, the old idler pulleys, and potentially the old water pump on the car. A kit replaces them all at once. This guide explains what goes in a kit, why each piece matters, and how to choose between the available kit configurations.

The components of a complete kit

A standard timing belt kit includes the belt itself, the main tensioner, one or two idler pulleys, and the small fixings (bolts, gaskets) needed for replacement. The tensioner is the spring-loaded or hydraulic device that maintains correct belt tension as the belt stretches slightly over its life. Idler pulleys are the non-driven wheels that route the belt through its path; their internal bearings wear over time and can become the noise source even when the belt itself is fine.

A "kit with water pump" adds the water pump to the same package. On engines where the timing belt drives the water pump, this is essentially mandatory — the access to the pump is identical to the access to the belt, so changing the belt without the pump is a guaranteed return visit.

Why a kit, not a belt

The tensioner sets the belt’s working tension. A worn tensioner can’t maintain the new belt’s tension correctly — the belt may slip, may wear unevenly, may run loud. The idler-pulley bearings wear on a similar timescale to the belt; a new belt running over an old idler will cause noise within months and eventually a bearing seizure that takes out the timing system.

The water pump on belt-drive engines is the highest-risk component. It’s driven by the belt at engine speed, runs in coolant, and its internal bearing eventually fails. When it fails, coolant escapes onto the belt — and the belt then loses traction and skips teeth. So even if the pump isn’t leaking yet, replacing it during the belt service costs nothing in additional labour and prevents the most likely future failure.

Choosing kit configuration

"Belt only" kits include just belt, tensioner and idlers — appropriate for engines where the water pump is not driven by the timing belt (separate auxiliary belt) and is independently accessible.

"Belt with water pump" kits are appropriate for engines where the water pump is driven by the timing belt. On most modern European petrols and diesels (VAG TDI, BMW N47, PSA HDi), this is the right kit.

Some engines also have a separate auxiliary drive belt (alternator, A/C compressor) — replacing this at the same time as the timing belt makes sense because the auxiliary tensioner often has to come off for timing belt access. Some kits include the auxiliary belt and tensioner too.

Brand and quality

The two dominant OE timing-belt kit suppliers are Continental ContiTech and Gates. INA (part of Schaeffler) makes kits for many VAG and BMW applications. Dayco and SKF supply some OE applications. The kit-makers source matched belt, tensioner, idlers and pump from compatible suppliers — buying a complete kit ensures all components have been engineered to work together over the new belt’s service life.

Buying components individually from different brands occasionally saves money but loses the matched-tolerance assurance that comes with the kit. For a part that controls engine survival, the matched-kit option is the right one.

Quality of fit

Look out for the OE part number cross-reference on the box. A quality OE-equivalent kit will list the specific OE part numbers it replaces — that gives confidence the kit has been engineered to the OE specification rather than generically dimensioned.

Service interval and replacement triggers

Replace at the manufacturer’s interval (60,000–100,000 miles depending on engine) or every 5–7 years, whichever comes first. Replace early if there are signs of belt aging — visible cracking on the belt teeth, fraying at the edges, oil contamination, or unexplained noise from the timing area.

Find timing belt kits matched to your engine on the Timing Belt Kits collection. Buying the kit is the small premium that prevents the most expensive engine failure most cars suffer.