I had a stripped water pump securing bolt on my big block engine. With only three bolts of the same size bit one of perhaps 1/2" longer securing the pump to the engine block it seems that someone in the past had used the longer bolt in a shorter bolt position.......perhaps them overtighened it, bottoming-out in the 'blind' tapping in the block and stripping the thread. Water leaks from under the water pump where it secures to the block were a continual problem. The 'tappings' in the engine block are 'blind'......so if drill and tapping them fractionally oversize to accept a Helicoil or Timesert they don't work so well when the new tap provided (for the new thread you'll need to cut) is equivalent to a first or intermediate tap with no final or non tapered 'plug' tap allowing a thread to be cut the complete depth of the 'blind' hole.
Ordinarily it wouldn't be a issue......you would simply drill deeper down in to the 'blind' hole.........problem being the risk of 'piercing' the water gallery........and being cast iron, not the easiest material to cut a thread in to.......and even worse it being on the front of the block access is poor so to dothe job really well its an engine-out job..........
