I subscribe to an excellent free blog by master surveyor and mechanic Steve D'antonio. his latest article is about prop shaft alignment. I've watched a cruise be interrupted when a friend's engine broke its mounting bolts and tore the key right out of the p-shaft from 35 years' lack of maintenance. here's the article:
http://stevedmarineconsulting.com/the-ins-and-outs-of-engine-and-shaft-alignment/
http://stevedmarineconsulting.com/the-ins-and-outs-of-engine-and-shaft-alignment/
