Recently all sleeper trains between Bangkok and Chiang Mai have been arriving at these cities up to 4 to 5 hours late. This is due to slow running over the washouts - up to 10 - in the northern hilly regions, and also extensive track renewal - the old wooden spiked sleepers are being replaced by concrete sleepers and pandrol clips. This info. has not been reported on Seat61 or the Thai Railway websites. However many passengers arriving at Chiang Mai recently have been reporting arriving very late with some resulting complications in joining tours, elephant camps, or arriving late at accommodations etc.
Typically trains 51 / 52 have been taking 19 hours to do the complete trip.Edited: 17 October 2012, 02:28