I have bmw 325is sedan 1995 model.engine broke so mechanic put in used 1995 525i engine which he said is ok.

alternator was replaced with a refurbished 325is and the alternator belt changed.new belt began to wear out within minutes after installing.took it to mechanic,relpaced belt.after 60 miles noticed belt edge had cut away.mechanic concluded the alternator was the problem(may be slightly short in length).

Help me find a solution
I have bmw 325is sedan 1995 model.engine broke so mechanic put in used 1995 525i engine which he said is ok.
Sounds to me like it has the wrong pulley. But looking at the part numbers, they are identical. See if you can get a pulley for the 525 and see if there is a difference. Also does the belt look like it is sitting at an angle? It should be perfectly straight from the crank pulley to the alternator pulley. Any side tension will wear it out just as you have said.
I have bmw 325is sedan 1995 model.engine broke so mechanic put in used 1995 525i engine which he said is ok.
Without seeing the car it is hard to make a conclusion. Chances are you might need a 525 alternator, or just simple adjustment of the pulley, another possibility is that the pulley on the car might be bent, check the number of lines from the belt and the pulley. There should be no problem from the engine because it is the same engine 2.5 liters. Whatever the reason, its not your problem, the mechanic should know and take care of it, unless hes a friend doing you a favor.