BMW Lower Chain
Tensioner Replacement
Wayne R. Dempsey

Difficulty Level: 3
Difficulty scale: Adding air to your tires is level one
Rebuilding a BMW Motor is level ten

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     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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