I am building a Clayton steam lorry. At the moment I am working on the crankcase and its components and have a problem with the pitch (distance apart) of the water pump gears and wonder if someone can help with an explanation. The drawing gives the distance apart of 1.12 inches for the distance between the driving gear and the idler and also 1.12 inches between the idler and the driven gear. I find that the distance apart should be more like 1.25 inches between driver and idler and idler and driven gear but this would be put the driven shaft out of position along the centreline. I can get around this by offsetting the idler gear as the driver gear is fixed to the crankshaft and I want to keep the hole position for the driven gear. I can plug the hole I drilled for the idler bearing. The drawing shows the three gears on the same centre line.

Can someone point out where I have gone wrong? The driver and driven gears are 45T 32 DP and the idler is 35T 32 DP.

thank you, Andrew Beasley.