Technical

A question for the experts - what's the best method to ensure a good seal between the rotary valve and the front face of the valve body ? I've heard one suggestion of lapping it in with jeweller's rouge and another suggestion to use toothpaste. What's the best method ?

Loco symptoms: Fully open regulator, hot engine - all the steam vented up the chimney with minimal torque applied to the wheels (barely turning them). If I cool down the loco, remove the rotary valve and "over" oil it with a goodly dollop of steam oil between the valve and the front face, then start again: the loco runs for a few minutes and as the oil is gradually used up, it slows down to a stop.

For reference, this is an A3 (DTFS actually) and I can't see any obvious scratches or other wear on the face of the valve block. I've tried with a new rotary valve from Nick-the-shop with much the same results.

Thanks in advance for all your helpful suggestions,

David