tyler's report led to an unusual alteration. it was discovered that the loading gauge of the line was too small. the internal width of the overbridges was only , but the railway's passenger carriages were wide. this left less than clearance on either side, which was less than the minimum required clearance of . to alleviate this problem, mcconnel proposed that the doors on one side of each carriage be permanently barred and the track slewed off-centre beneath the bridges. this would allow adequate clearance at least on the side with doors and mean that passengers could get out of the carriages if the train stopped underneath a bridge. tyler agreed to this arrangement, and to this day all carriages on the talyllyn have doors on one side only, an unusual feature for a public railway. this feature is however shared with the neighbouring corris railway, though for different reasons. tyler also required that improvements be made to the railway's first two steam locomotives, as locomotive no. 1 suffered from excessive "vertical motion" and no. 2 was said to suffer from "horizontal oscillation". no. 1 was returned to its manufacturer where a set of trailing wheels was added to reduce the rear overhang. the springs on no. 2 were adjusted and the crank pins shortened to reduce its oscillation.