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Exhaust Manifold Replacement
 
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Pelican Technical Article:

Exhaust Manifold Replacement

Tom Morr

Time:

5 hours5 hrs

Tab:

$10 (nuts), $9 (gasket) $718 (new manifold)

Talent:

****

Tools:

5mm hex/Allen wrench/bit, 10mm, 12mm, 13mm, 22mm wrenches/sockets, ratchets, extensions, wobble joints, crescent wrench, E10 Torx socket

Applicable Models:

Mercedes-Benz R170 (1998-04)

Parts Required:

Split-collar nuts, gasket, manifold or header

Hot Tip:

Soak all nuts in penetrating lubricant early and often

Performance Gain:

Fixes leaks at the exhaust manifold or gasket

Complementary Modification:

Replace the air filter

Exhaust leaks are annoying, particularly at the exhaust manifold. The engine's heat-up/cool-down cycles cause the exhaust manifold, gasket, and hardware to expand and contract. Over time, the parts can fatigue and fail.

The worst-case scenario is a cracked exhaust manifold. When this happens, SLK owners are often faced with a dilemma: attempt a repair, source a new or used manifold, or swap in a header.

Regardless of your choice, the removal/replacement process is the same. It isn't necessarily difficult. However, access to the manifold's split-collar nuts is tight, particularly the ones on the lower side of the exhaust manifold's mounting flange. Shorter wrenches can achieve a half-turn per stab. Repeat this process seemingly ad infinitum until all of the nuts are removed. Incidentally, some brands of ratcheting wrenches are thin enough to remove at least one of the lower bolts.

The split-collar nuts need to be replaced any time the exhaust manifold is removed. These nuts are available for $0.75 each from Pelican Parts, #000-990-32-50-M36.

Mercedes-Benz also recommends using dots of exhaust sealing compound on the gasket and other dry-assembly exhaust joints, such as the exhaust manifold's outlet to the exhaust pipe. This is a topic of debate among hands-on owners. The compound fights exhaust leaks but makes disassembly more difficult the next time.

Anyway, the OE part number for official Curil T sealing compound is 001-989-25-20-MBZ. Pelican Parts also offers Wurth Exhaust Assembly Paste, #WRTH-100045.

Liberally dousing the exhaust manifold's nuts with penetrating lubricant multiple times --a day or more in advance, with the engine hot and cold -- can help them come off easier. Other preliminary steps include raising and securing the vehicle on jack stands. Also, removing the lower engine cover and right-side crossbrace will improve access to the lower nuts, oxygen sensor, and the two bolts that connect the exhaust manifold to the exhaust pipe.

The duct between the air box and supercharger intake needs to be removed, too. (We pulled the air box and supercharger for other articles, making photos and overall access easier.) Please see those R170 articles for details about these steps.

In general, prepare by collecting every 12mm socket, wrench, ratchet, wobble joint, and extension you own. On our project car (a pre-facelift 2000 SLK230 Kompressor), a 3/8-inch ratchet with a standard socket and extensions proved successful for the top nuts.

Underneath, don't plan on using sockets. Longer combination wrenches are good for breaking the nuts loose, then a stubby wrench allows longer throws, maximizing turns per wrench bite. Ratcheting wrenches can expedite removal of some nuts. Also, the secondary air valve's pipe can be easily removed from the fitting on the engine block. We used a crescent wrench to loosen its nut, which is larger than the 22mm wrench used for the oxygen sensor.

Unbolting the exhaust manifold from the primary exhaust pipe requires removing the oxygen sensor. (Please see the sensor and exhaust pipe articles for details.) Then a 13mm socket and long extension can be used to remove the two bolts. For reassembly, the exhaust pipe might need to be loosened at its U-bolt and crossmember mounts to align with the exhaust manifold.

The torque spec for exhaust manifold nuts and bolts is 20 Nm.

Begin by removing the upstream oxygen sensor.
Figure 1

Begin by removing the upstream oxygen sensor. Its plug is located in a clip between the transmission dipstick and firewall (arrow).

Looking up from behind the right-front tire, the oxygen sensor (red arrow) must be removed.
Figure 2

Looking up from behind the right-front tire, the oxygen sensor (red arrow) must be removed. Access is tight, so a normal O2 sensor socket doesn't work well. If the sensor has anti-seize on its threads, a 22mm wrench or even a crescent wrench should work for breaking it loose. Then the two bolts (yellow arrows) that connect the exhaust pipe to the exhaust manifold can be removed.

While underneath the car, have a go at the exhaust manifold's lower nuts.
Figure 3

While underneath the car, have a go at the exhaust manifold's lower nuts. Three of the five on the SLK230 Kompressor are indicated here with arrows.

The rearward air duct between the air box and supercharger inlet (blue arrow) has to be removed.
Figure 4

The rearward air duct between the air box and supercharger inlet (blue arrow) has to be removed. Next off is the exhaust manifold's heat shield, which is held on with four cap screws having 5mm Allen heads (yellow arrows). Removing the oil separator (purple arrow, secured by two screws that use a 5mm Allen wrench) also improves wrench clearance. The pipe that goes to the supercharger air valve (red arrow) is bolted to the supercharger housing (E10 Torx socket and 10mm wrench) and underneath at the engine block with a large nut; we used a crescent wrench there.

Once all 11 nuts are off, the exhaust manifold can be removed.
Figure 5

Once all 11 nuts are off, the exhaust manifold can be removed. If the studs come out with the nuts, dip one end in grease and finger-thread that side back into the engine. We removed the supercharger for a different article, which freed up considerable space--but theoretically isn't required.

The new exhaust manifold gasket (arrow) installs over the studs.
Figure 6

The new exhaust manifold gasket (arrow) installs over the studs.

The torque sequence is rear to front, moving to the bottom when that's the next forward-most nut.
Figure 7

The torque sequence is rear to front, moving to the bottom when that's the next forward-most nut.

Once the exhaust manifold is in place, the primary exhaust pipe might need to be loosened so it can be re-positioned slightly to align with the manifold.
Figure 8

Once the exhaust manifold is in place, the primary exhaust pipe might need to be loosened so it can be re-positioned slightly to align with the manifold.

If reusing the existing exhaust manifold, clean its flange's mounting surface with a wire brush or other suitable method.
Figure 9

If reusing the existing exhaust manifold, clean its flange's mounting surface with a wire brush or other suitable method. The bulk of the job is accomplished with 12mm wrenches and sockets.

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