I want to set up a warranty based on that condition: the warranty expires after one year or after the motor has worked for 4000 hours. How I can handle this?

The warranty itself only has the effective and expiry date. That takes care of not providing coverage beyond a year. You can't do the counter in the coverage terms - that only allows ceilings on the dollar amount of coverage provided.

I assume you know the uptime hours by use of a counter in an inspection that occurs at each maintenance. You could create a custom report/update that would find all the serialized items with a counter reading over 4000, and it could either report on or automatically update the serialized item to remove it's warranty (which is as simple as blanking out the warranty template field in the serialized item details).

Or if you don't want to have to create a report/program, you could trigger a maintenance notification when the counter exceeds 4000. The maintenance notification would be for a reference activity like "cancel warranty". Then the contract/billing coordinator would monitor orders that get this reference activity. When they see it, they'd remove the warranty off the serialized item, and potentially off that order, and then they'd just delete the reference activity off the order.

I think some of this functionality is 10.3 or later (inspections, maintenance notifications, ...), but there are somewhat equivalent methods in 10.2.1 and previous.

Hope this helps.