Keith, there's probably a number of fellas here that have used a ridge reamer and made it work, and some that have screwed up when using it; they might not have chimed in yet. I agree with Matt Wilson though. Please don't use it and risk making a mistake you can't undo. I haven't used a ridge reamer on an engine, but I know how they work. As a machinist, it's something I'd call a "hack" tool. There's no way that thing is square, and no way you're going to know exactly how much material you're going to remove. In addition, it's really not even a reamer, it's an adjustable bore bar at best. I've reamed and bored thousands of holes on manual mills and lathes, and on the (3) $500,000 each dual spindle dual turret Nakamura CNC lathes I operate at work every day. I've used adjustable bore bars (and true adjustable reamers), and this reamer that's being discussed here is something I would never consider using on a good engine. Please don't use it.