Martin's Spur 80, part 7 Martin now sets out to build the Mason Bogie's full complex valve gear. The crossheads are backed in brass with wood outer plates, while the crosshead guide and piston is brass. The entire fully working valve gear is made of wood! Martin's Spur 80, [ part 1 ] - [ part 2 ] - [ part 3 ] - [ part 4 ] - [ part 5 ] - [ part 6 ] - [ part 7 ] - [ part 8 ]