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Audi ur-Quattro (10 Valve) Exhaust Manifold

The 10V ur-quattros (WR, WX, MB and GV engines) are notorious for cracked exhaust manifolds. The cause and solution are contentious. The same problems occasionally occur on the Audi 100 and Audi 200 1B and MC engines.

The primary cause of manifold cracking is not heat, design or poor metallurgy on Audi's part. It is the unnoticed failure of the right side engine mount causing the right edge of the sump to rest on the subframe or the exhaust downpipe to contact the body. This translates into serious upward hammering on the lower right edge of the engine block. The entire weight of the turbo and most of the weight of the downpipe is carried by the exhaust manifold, which is a cast component not designed to take torsional or impact loads - and it fails.

An experienced eye can spot a defective engine mount by looking underneath the front of the car from some distance in front - the apparent shape of the sump protruding into the ground clearance is very distinctive. For the less experienced, the classic test is passing a thin folded strip of newspaper over the subframe and trying to slide it round the rear right corner of the sump. If this cannot be done, the sump is resting on the subframe and exhaust manifold failure is purely a matter of time.

Checking for manifold failure is slightly more difficult. The area around the upper exhaust manifold has significant airflow even with the vehicle stationary, largely from the alternator's cooling fan. The traditional chicken-feather-on-a-stick appproach doesn't work - tie-wrapping the end of a plastic tube to a length of stiff (coat-hanger?) wire and listening to the other end can sometimes localise a crack. The best technique is to remove the front right headlight and concertina hose, and check along the upper surface of the manifold with an inspection light such as an Aaron Bend-a-Light Pro for the tell-tale white and/or light brown traces of a crack. There are two principle locations - one underneath the manifold to the rear of the turbo mounting flange caused by the turbo's downward hammering effect when the engine drops onto a retreating subframe, and one at the side of #4 port caused by the subframe hammering upward on bumps.

Attempts to repair manifolds by welding were originally unsuccessful, although a controlled experiment using nickel-powder welding and new engine mounts is now in progress - nine are now running in the UK with no problems reported so far.

In most cases, it is necessary to remove the cylinder head. Although the manifold itself can usually be removed fairly easily, replacing the exhaust manifold studs is HIGHLY advisable and this normally requires benching the head.

Once the head is off, the non-manifold side can be stripped back to a flat surface. With the head resting on this surface, the manifold side is uppermost and can be worked on.

It is VERY easy to shear off studs, especially if the manifold has been undisturbed for a number of years. First remove any finger-nuts that are present and use a power-driven wire brush to remove as much corrosion as possible from the protruding threaded portion of the studs. Then soak the nuts and studs in a penetrating lubricant such as Lubrice, Halford's Penetrating Oil or Plus-Gas, if possible overnight. WD-40 has no discernable effect. Finally apply removing force to the nut axially, i.e., directly in line with the stud using a socket, extension and T-bar. The ideal combination is a good quality 13mm (sometimes 12mm) 1/4" drive socket on a good 6" extension, adapted up to 3/8" or 1/2" drive T-bar. Carolus, Bahco and Teng sell good quality waisted sockets that make life even easier. Avoid using spanners (wrenches) that apply sideways forces on old studs if at all possible. Use a to-and-fro motion, moving the nut a little further each time, then back, and applying plenty of lubrication. Expect to take up five minutes per nut. If you encounter real stopping resistance, back the nut off and clean the thread again.

As always, heat - preferably oxy-acetylene, although propane is better than nothing - can be very useful in freeing up stuck nuts.

Inevitably some studs will come out with their nuts. Once all the nuts are removed, take off the manifold and remove the remainder of the studs. A FACOM 287B.8 roller clutch-type driver or equivalent is ideal - using the same to-and-fro technique with lots of lubrication. Avoid using cam-type stud removers and the 'two locked nuts' trick if at all possible. Even if an exchange head is to be fitted (exchange heads come prefitted with studs) the exercise is useful.

If the engine mount is being replaced, the upper nut (holding the engine support bracket to the mount) should be released while the weight of the engine is still on the mount. Only then should the engine be jacked up to relieve pressure on the mount - once the lower nuts have been loosened a few turns, the engine mount should rattle - indicating it is carrying no weight and it is safe to replace it. Note that Audi's ETKA system is a little confusing regarding spacers - ETKA AQS/85/1/99 illustration 21-00 shows that item 19 and 20 for the right mount spacers (the ones you would expect) have no valid part numbers. But there is an item 19A listed for the left side. Checking the text shows that there is a version of 19A valid for the right side, although it is not shown on the diagram. It is critical that this spacer (443 199 488A) is present - its 6mm thickness makes all the difference. Check also that the engine mount is properly protected from heat, but do not fit any additional heat shielding as this tends to block manifold cooling airflow at speed. If other modifications (such as a dump valve) are fitted, ensure they don't block this airflow. The Type 44 has a special hose running from the front spoiler - check that this is in order.

Refitting the manifold is the reverse of removal. Observe the torque settings - noting that the studs themselves should only be finger-tight.

Correct nut (Philidas PIL-YZP-M8)                       Wrong Nut

Parts required:

035 129 591BC Exhaust Manifold
N 016 153 1 Plug (WX, MB, 1B, MC)
N 013 832 6 Sealing Washer (WX, MB, 1B, MC)
443 199 381C Engine Mount
857 199 386A Heatshield (WR, WX, GV, MB) - Type 44 uses an air duct.

For the 1B and MC engines, there is an alternative exhaust manifold:

034 129 591AC Exhaust Manifold, Cylinders 1-3
034 129 592 Exhaust Manifold, Cylinder 4-5
034 129 933 Retaining Clip (x2)
034 129 955 Connecting Pipe (x2)
034 129 903 Corrugated Pipe

This option is currently some £300 more expensive and no more reliable than a properly installed one-part manifold.

An alternative manifold is also available from Dialynx. Before selecting such an item, consider the following:

1. Can you reach all of the nuts from above, i.e., using a socket and T-bar without putting sideways loads on the studs? Is there sufficient clearance for a socket on each nut? It is important to avoid sideways loads on old studs - if the manifold is to be removed at some point in the future, this can be a consideration.
2. Are the seats for the thick washers (N 900 955 01) ground flat or left as cast? If they aren't flat and parallel to the mounting surface, they may place non-axial loads on the studs when tightened, leading to later fatigue failures.
3. WR and related engines - does it have a connection for the wastegate control pipe (035 198 133A) or does the engine have to be converted to use inlet manifold pressure instead of exhaust manifold pressure? If this is done, the original pipe should be retained for possible future use as it is a VERY expensive part.
4. Does raised lettering on the upper surface interfere with access to the inlet manifold screws? See the notes on an easily made special tool for the inlet manifold screws in the head removal instructions - these are relevant even if the manifold is changed with the cylinder head in situ.
5. Does it have the same internal runners as Audi's manifold - where four ports are paired to improve scavenging - or is it simply a large empty space internally?
6. Does it line up the wastegate support brackets and downpipe so that they fit to other components without problems?
7. Are the ports sized the same as Audi's?

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