A retainer device is provided suitable for supporting a valve shaft in a variable intake system. Preferred retainer devices can stably support a valve shaft of a variable intake system and may suitably include a shaft support part that can engage a valve shaft of the variable intake system; a fork part that can engage a valve shaft locking bolt; and a stop part spaced from the fork part by a distance sufficient to position the locking bolt between the fork part and the stop part. In preferred systems, even if a valve shaft locking bolt fastening the valve shaft is undesirably loosened during engine operation, the locking bolt is prevented from being completely removed from the retainer, thereby avoiding potential engine damage.