1998 Chevy Silverado harmonic balancer

I recently had work done on my water pump. There was a piece broken on the cover to the harmonic balancer. They covered the hole with jb weld. The vehicle then started to shake when you drive it. It did not do that prior to the work. Could the piece be in there throwing it off balance, and if we take it out will it run correct again? If it need to be replaced how much does it cost to replace it?