Timing Pulley Drops Off

Our daughter and son-in law have a 1996 Subaru Outback with 134,000 miles. About 4-5 months ago they had the timing belt replaced.

Three weeks ago the pulley (bolted to the end of the crankshaft) that drives the power steering and air conditioning, fell off. The mechanic has replaced the pulley, bolt and lockng pin and wants to charge $275 for the job. He states the pin broke, causing the pulley to wobble and wear, the bolt to come loose and the pulley to drop off.

When the timing belt was replaced, assuming all the parts were in good condition and the bolt attaching the pulley to the end of the crankshaft was tightened to the proper torque, is it feasible the locking pin would break and the remainder of his sequence of events occur? (Question #1)

I think his work is partially, if not totally, responsible for the problem and he needs to cover the cost of correcting the problem. Is this a reasonable request? (Question #2). I am not trying to hammer him. He is a good person, but I question his logic on this problem.

Thank you for your response.

Also, thank you for your weekly show. It is professional and stimulating, and the laughter is good for the soul.

You already posted this question here: http://community.cartalk.com/posts/list/1510409.page