How come Bob Vila ,who appeared on many first season episodes(always besting Tim,by the way,)never appeared on any second,third,fourth,fifth,sixth,seventh or eighth season episodes?

Tim was probably getting tired of being humiliated by Bob!

He only appeared in one episode of season one. I think he was also in seasons two and three, but only once.

I like the Episode where Tim tried to break Bob Vila's steamroller on tool time.
"A very dangerous move on Tool Time".