If it is only the harmonic balancer, they are attached to crank pulley by means of a rubber damper and over time when this dampaer fails, the outer ring would fall off. The central pulley would still be intact.
Otherwise what Rasmataz said is correct. Under such circumstances you would have to check the crankshaft for wear. If it is worn ecentric, a new pulley is not going to work well ans t could also wobble and this would result in central bolt breaking off sooner or later.
Sunday, December 26th, 2010 AT 2:20 PM