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.
The BMW inline engines are driven by a chain that links the timing of the camshafts to the rotation of the crankshaft. Sometimes, the tensioner grows weak and begins to fail, causing the engine to give off an annoying rattle on deceleration. This rattle grows louder as time passes and may become more noticeable at slow speeds. While many people misdiagnose this problem as a failing VANOS unit (see our article on Camshaft Timing and Vanos Unit Installation), it's more likely to be a failing lower chain tensioner. This may occur in high-mileage or even some low-mileage engines; it doesn't seem to be uniformly related to the total number of miles driven.
BMW redesigned the tensioner in later years of the E36 and offers an upgraded tensioner that can be used in place of the older one on 325/328 six-cylinder models. Thus, replacing the chain tensioner, which is a very easy process, typically solves the problem of the noisy chain.
Using a 32-millimeter deep socket, carefully remove the chain tensioner from the lower front of the cylinder head. Place a rag or paper towel under the tensioner to catch any excess oil that may leak from the engine. When removing the tensioner, proceed slowly, as it is under tension when you release it.
Installation is as simple as removal. Place a new sealing ring on the tensioner, and insert the tensioner into its hole in the cylinder head. At this point, the two small fingers on the tensioner should line up with a mating ridge on the chain guide inside the cylinder head. If this doesn't happen, you will have a very noisy, rattling engine when you start it up. To guide the installation of the chain tensioner, stick your finger in the hole in the cylinder head so you can feel the ridge on the chain guide. Hand tighten the tensioner to start, and then use a torque wrench to tighten the tensioner to 50 N-m (37 ft-lbs) for the early-style tensioner and 40 N-m (30 ft-lbs) for the new-style tensioner. Use a new aluminum sealing ring between the tensioner and the engine block when reinstalling the tensioner.
When you start up your engine, listen carefully--it should run very quietly. If the noise is worse, however, then you probably didn't align the tensioner properly with the chain guide. If that's the case, remove the tensioner and reposition it. If the engine still makes noise, the problem may lie with the upper chain tensioner (also known as the VANOS chain tensioner) or the VANOS unit itself. In that case, see Project 13.
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Shown here is the chain tensioner removal from the bottom of the E36 six-cylinder engines. This early-style tensioner has an inner piece and an outer shell (still attached to the cylinder head--orange arrow). When you reinstall the chain tensioner, make sure the groove in the tensioner fits precisely into the mating groove on the inside chain guide. If these two parts don't line up, you will have a lot of chain noise when you first start up the engine.
The upgraded one-piece tensioner (part number BW-11-31-1-405-081). This is a good upgrade, as the early units had a tendency to wear out. The inset photo shows the older-style chain tensioner for the E36 six-cylinder engines.