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Audi ur-quattro MB Engine Cambelt and Idler Roller

At the end of the 1988 model year - nominally starting at chassis number 85-J-900644 - Audi started fitting an updated version of the MB engine - changes made to the donor MC engine. The principle changes were a new inlet manifold with a spilt fuel catching tray and drain, moving the high-pressure wastegate frequency valve line to throttled (vs earlier unthrottled) air, a 142-tooth cambelt, cam gear, crank pulley, idler roller and water pump.

If fitting a new short block from Audi, it is important to check that the idler roller (supplied with the block) is the correct size - the later one is significantly smaller. Fitting the older (larger) idler roller to a Series 2 engine with a 142-tooth belt belt will destroy the front cam bearing and render the cylinder head unusable. Audi supply the roller, its bolt and a new alternator strap pivot bolt with short blocks because both bolts are an integral part of the oil pump.

The main visual clue is the front of the inlet manifold - on an earlier engine it is rounded and pipe-like - on the later engine a raised lip creates a kind of tray. This is NOT conclusive - 85-J-900688 has a Series 2 engine with a Series 1 inlet manifold. The number of teeth (142 for the later belt, 120 for the earlier one) is definitive.

For convenience, the two versions of the MB engine are referred to as "Series 1" and "Series 2". The last "Series 1" engine - fitted to chassis 85-J-900643 - was supposedly MB001388.

Problems arise because of the way Audi stocked engines and fitted them to cars - typically a one to three month lag. A number of cars are known to have Series 1 engines with 120-tooth timing belts even though the VIN suggests they should have Series 2 engines with 142-tooth belts. In the UK, the following is an incomplete list of these VIN numbers:

Kerbside Motors would appreciate the VIN numbers of other late cars with Series 1 engines, in order to complete the above list to assist our parts suppliers.

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