Motorcycle Repair: Liability, belt pulley, small claims court

Question
I had  a belt pulley on my Motorcycle repaired by a local motorcycle shop.  Upon completion I paid for the services and parts.  I was asked to bring the bike in a week later to ensure the bolts had remained tight, which I did.  A week later the bolts became loose and now caused damage to my back wheel which now needs to be replaced. The shop did not put lock tight on properly and that is what caused the problem.  They, however, claim they did do it properly.  Bottom line is they said they fixed the problem and now it has caused more damage.  I offered to pay half of the repair costs if they pay the other half.  The owner of the business will not do that.  Now I am stuck with paying and additional 500.00 to fix my bike.  What should I do?  Are they responsible for the repairs?

Answer
I guess my question to them would be, if they did it right why did it come apart and damage the bike. If I were you I would not accept that. And also, why should you pay an additional amount for work that is not your problem. Yes, they are responsible for the repairs. I think, if I were you, I would take them to small claims court and let a judge sourt it out.
Good luck and happy riding
Mike