The exact parts — OEM, plus what owners actually use. Skip the internet hunt.
Timing belt (4.2L 40v V8)
OEM078109119JOwners useContinental/ContiTech 078109119J, ContiTech CT1033 / TB297, Dayco 941064$35–$75
Genuine Audi PN confirmed on parts.audiusa.com and fits S8 D2 4.2 40v (engine AYS). The D2 S8 only ran 2001-2003 with the AYS 40v V8, which uses the 078-prefix belt 078109119J (supersedes 078109119C/G/H). NOTE: the EARLY D2 A8 1997-1999 (ABZ/AEW engine) uses a DIFFERENT belt, 077109119D — that is th
Hydraulic timing belt tensioner / damper
OEM077109479DOwners useNTN 077109479D, INA 533 0036 30, VAG 077 109 479 D$50–$90
NTN-supplied hydraulic damper that works with the tensioner lever to set belt tension. Confirmed fitment across C5 A6/S6 4.2, D2 A8/S8, D3 A8 4.2, RS6 and Touareg V8 (ECS/Europa/FCP). Replace every belt service. Verified live across multiple OE vendors.
Timing belt tensioner roller (lever-mounted)
OEM077109485EOwners useINA 531 0561 10, Ruville 55939, SKF VKM 11103$30–$70
Tensioner roller on the lever unit; vendors list 077109485E/F for the 4.2 40v kit (Cascade German / NGP / blauparts 'Deluxe' kits). Replaced with the belt. PN family confirmed across multiple kit listings; exact suffix (E vs F) varies by supersession.
Timing belt idler roller (large)
OEM077109244EOwners useINA 532 0329 10, Ruville 55937, 077109244E$20–$50
Large idler/guide roller in the 4.2 40v timing system; listed in the OE deluxe kits for A6/S6/A8/S8 4.2 (Cascade German Parts, NGP). Bearing wear-item replaced with the belt.
Timing belt relay/idler roller (small)
OEM077109244COwners useINA 532 0236 10, Ruville 55936, 077109244C$18–$45
Small relay/guide roller in the 4.2 40v timing layout; paired with the large idler in the OE kits (Cascade German / NGP). Replaced with the belt.
Water pump (metal impeller) with gasket
OEM077121004POwners useGraf PA-857, Hepu P530, Geba$70–$130
Genuine Audi PN 077121004P confirmed on parts.audiusa.com for the 4.2 V8; updated metal-impeller design (early plastic-impeller pumps fail). Always replace during the belt job since it is belt-driven. Older kit listings cite 077121004M — that is a prior supersession of the same pump.
Water pump gasket / seal
OEM078121043AOwners useGenuine VAG 078121043A, Elring, Victor Reinz$3–$12
Genuine Audi water-pump gasket confirmed on parts.audiusa.com / Pelican for 4.2 V8 (A6/A8/S6/S8/RS6/Touareg). Usually supplied with the OE pump but listed separately as a required sealing consumable for the job.
Thermostat (4.2 V8, with O-ring)
OEM077121113DOwners useMahle/Behr TI 31 87 (082°C), Wahler, Genuine VAG 077121113D$15–$45
Commonly replaced while the front of the engine / cooling system is open during the belt+water-pump service. 077121113D (82C, Mahle, w/ O-ring) is the genuine 4.2 V8 thermostat per parts.audiusa.com and Europa Parts. Secondary/optional consumable, not strictly part of the belt itself — included beca
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