Cam Chain Tensioner Upgrade, Left Side BMW Hexhead & Oilhead 11 31 7 688 629 11 31 7 656 922The original left cam chain tensioner piston allows the oil to drain out of the tensioner housing when the engine is shut off. As a result when you first start your engine, you hear a momentary clanking noise from the left cylinder. This is the left cam chain smacking into the tensioner rail until the oil pressure builds up behind the tensioner piston. Over time this can cause the tensioner rail to break which is a costly repair. This new style