Fits N62 engines. There are two cylinder heads for this engine and there is a chain for each cylinder bank. The camshafts are driven by the crankshaft by what BMW call “maintenance free” chains. Unfortunately this is not the case as the chains begin to wear around 80,000 miles leading to poor running of the engine which can lead to engine failure if the timing chain breaks. BGA recommend changing the chain, guides and tensioner to ensure smooth running and prevention of further problems.