Your multi-engine rating is revalidated by a proficiency check with an Examiner within the 3 months prior to it expiring. In addition, you must also, within the period of the rating, have completed 10 route sectors, each of which consists of take-off, at least 15 minutes of cruise, then arrival, approach and landing. If you have not met the requirement for 10 route sectors, you may substitute 1 route sector which must be flown with an examiner, and this may be part of the proficiency check.
The IR is also renewable by proficiency check. If it is a multi-engine IR, it may be renewed at the same time as you renew your multi-engine rating.
All of this information can be found in
LASORS
FFF
--------------