David wrote:- > I'm still trying to get it to run smoothly, but I am getting a large > amount of steam out of the stack and the boiler can't keep up, so it seems > the valve is not seating. I did polish the valve face with crocus cloth so > I know it will take a while for the valve to bed in.
Give your crocus paper to a clockmaker and get a sheet of glass and a piece of 400-600 grit wet and dry emery paper. It's a common misconception that slide valves should be polished to mirror smoothness. What is actually needed is that they be FLAT but with a finely scratched surface to hold oil/water for lubrication. Place the emery, rough side up, on the sheet of glass, add water, and rub the valve across it in a straight(ish) line with plenty of pressure to keep the emery flat. After a few strokes, turn the valve through 90 degrees and give one stoke. If all the scratches are in one direction, it is flat. Now comes the important part. Wash the valve thoroughly and rub it firmly on a piece of good quality writing paper. The paper will become blackened with all the emery dust which it pulled out of the valve face. Failure to do this part will result in scratches on the port face when you run the loco. I'm not familiar with Accucraft locomotives but, if at all possible, the cylinders should be removed and receive the same treatment. Ideally they should be completely dismantled to allow proper cleaning afterward. Some experts recommend lapping the two surfaces together. Maybe it works for them, but it cannot guarantee the two flat surfaces you need. Concerning the length of the valves, my understanding is that Accucraft locos use zero lap valves - i.e. 100% cut-off or non-expansive working. The length of the valve should be exactly equal to the distance between the outside edges of the steam ports, and the exhaust cavity should be exactly centred longitudinally. The eccentric should be exactly 90 degrees in advance of the crankpin and the valve position adjusted so that the ports open exactly on front and rear dead centres. The valve movement should be exactly twice the port width. This is true of all locos with a simplified single eccentric valve gear. Mike Chaney _______________________________________________ SSLiveSteam mailing list Send messages: [email protected] Cancel subscription: http://postfix.45mm.com/mailman/listinfo/sslivesteam Rules: http://www.45mm.com/sslivesteam_guide.html
