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Message: <blockquote data-quote="daveseech" data-source="post: 348671" data-attributes="member: 11434"><p>i think even for a 4 cylinder they do need some form of balancing or dampening as well. i just remembered my wife's minicooper s has a performance crankpulley installed by the previous owner which i didnt knew about. since having it we had the sc belt tensioner replaced 3 times in just one year. feeling frustrated as on one occasion the belt actually snap while driving, aaron @leforte suspected something wasnt harmonically right as the tensioner has fatigued failures on all occasion so he suggested to  have a look at the pulley and sure enough the pulley was a aftermarket unit. i have since replaced it back to the original bmw mini unit and its been almost a year with no issues. the power is minimally less but i felt the engine was much smoother after that. strangely the original unit doesnt have a harmonic balancers or dampers on them too but i guess what was stated by leforte that its balanced as a part of the rotating assembly its true. you change it and you upset the balance.</p></blockquote><p></p>