Dryer intermittently will not stay on.

When I press and hold the start button, the drum turns, heat comes on, and as far as I can tell the dryer is operating normally. However, when I release the start button, it immediately stops (Drum stops, heat stops as if the cycle was done). After some experimenting, I found that I could spin the timer knob several times (counterclockwise and clockwise) and after awhile I could press the start button (and release) and the dryer would stay on and function as normal (Complete a normal length cycle, appropriately dry, clothes came out feeling warm like usual). So for the past few months I've used my "spin the timer knob" trick to get my laundry done. However, this week it stopped working and dryer won't stay on. To attempt a repair, I replaced the timer motor with an appropriate replacement part. After replacement, the dryer seemed fixed for 2-3 loads. However, the same problem returned less than 24 hour after replacing the timer motor.

Any help is appreciated.