GK timing belt (791057) synchronises the crankshaft and camshaft with tooth-pitch accuracy measured in hundredths of a millimetre — preventing valve-to-piston contact that would destroy the engine if the belt skips or snaps. Belt construction data — Number of Teeth: 138, Width [mm]: 23 mm — reflects the tensile load the belt must sustain at peak RPM, with an HNBR or EPDM compound chosen for the specific temperature range of your engine bay. OE cross-references: 06A109119B, 06A109119C, 108011, 138AH23 and 26 more. GK timing belts are tested to OEM replacement intervals and carry a service-life certificate verifying the compound meets the manufacturer's durability specification. Timing belt replacement intervals vary by manufacturer — typically every 40,000–100,000 miles or 4–6 years, whichever comes first — and must be followed strictly because a snapped belt on an interference engine causes catastrophic valve and piston damage. There are rarely visible warning signs before a timing belt fails; some belts may exhibit surface cracking, fraying, or a glazed appearance, but many break without warning — this is why interval-based replacement is essential. Timing belt replacement is an advanced DIY job requiring careful crankshaft and camshaft alignment, a torque wrench, and engine-specific locking tools — budget 3–5 hours and consult a workshop manual for your exact engine code. When replacing the timing belt, always fit a new tensioner, idler pulley, and water pump (if belt-driven) at the same time — these components have the same service life, and a failed tensioner will destroy the new belt. Investing in a quality timing belt kit now prevents the most expensive engine failure a vehicle can suffer — a belt-related engine rebuild typically costs 10–20 times the price of the belt kit itself. Every part is dispatched from our UK warehouse with a 30-day money-back guarantee and free hassle-free returns.