This article is one in a series that have been released in conjunction with Wayne's new book, 101 Performance Projects for Your BMW 3 Series. The book contains 272 pages of full color projects detailing everything from performance mods to timing the camshafts. With more than 650+ full-color glossy photos accompanying extensive step-by-step procedures, this book is required reading in any 3 Series owner's collection. The book was released in August 2006, and is available for ordering now. See The Official Book Website for more details.
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BMW Exhaust Manifold Replacement
Cracked exhaust manifolds have plagued the E30 and E36 models through the years. The manifolds installed on these cars are made of cast alloy steel. This alloy is heavy and durable, but over the years, it can become increasingly susceptible to cracks. It's not uncommon to discover a loud exhaust leak coming from the engine compartment. If it's not a worn-out exhaust gasket, it's most likely a cracked manifold. A cracked manifold will introduce an exhaust leak into the system. Besides making the engine noisy, it can cause the engine to run roughly and erratically.
The exhaust manifold connects each cylinder's exhaust ports to the exhaust system. Before you go near the manifold, make sure the car is completely cold. To remove the manifold, you will need to remove the nuts from the exhaust studs on the head. A set of swivel sockets comes in handy, as they are great for reaching nuts in hard-to-reach places. It is highly likely that the exhaust studs will come out of the manifold when you try to remove the nuts. If this happens, replace the studs with new ones, as you cannot properly install the manifold again using the studs if the nuts are frozen on them. You won't know if the stud bottoms out in the head or if it's actually holding on the exhaust manifold, and that's why it's best to just use new studs and nuts.
On 1996-and-later cars, you have to remove the secondary air check valve and pipe from the exhaust manifold. Also, on some models, you may need to remove the oxygen sensor prior to removing the manifold (see our O2 Sensor Replacement article).
A word of caution: Always use new exhaust gaskets when reinstalling the manifold. If you reuse gaskets, you may introduce an exhaust leak into the system, which can result in a noisy engine and erratic engine performance.
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