why do my chains keep breaking

[flippy]

just an update,I bought 2" o.d. round tube with .25" i.d. and 3/8 wall thickness- I bought #50 sprockets and the #60 sprockets from surplus center- I made my own #50 sprocket assemblies very time consuming but I am saving money.When finished I will have all new sprockets,new inner axle bronze bushings and new #50 chain.How do I go about making new jackshaft with new sprockets? My jackshaft and t20 sprockets will be the only original 40 year old sprocketsThe jackshaft is 1.25 o.d. and .75 i.d The entire lenth of the jackshaft tube has a bronze bushing like the hollow axles-Is it possible to build a jackshaft with new sprockets or do I need to just buy one?