If Yamaha says that they won't pay for the other two hours. And I refuse to pay the dealer. He is going to tell me he won't release the bike to me. As I would never have given a customer back their vehicle after I done work on it.
Is this legal? Does the mechanic shop have the right to hold the vehicle as collatoral in a dispute?
Probably varies country to country, but the only right of this type that I ever heard of is, if you don't show up to pick up the bike and pay within 3 months of the finish date, they can sell the bike to recover their costs. (general services company law, same for dry cleaners for example).
If you dispute a bill, they have the legal right to persue payment, through the courts, and then normal debt collection. I don't know anything that says they can seize or hold your property.