Re: Mercruiser 470 inboard -- stern drive to inboard
Unable to find a mie 470 bell housing I slapped the mercruiser io bellhousing off my 190 onto my cnc machining center. Using a circle center finding routine on the machining center I found the center of the existing opening and used that as an estimate of the centerline of the crankshaft. Working from that center point I drilled a borg warner bolt pattern into the bellhousing, machined an 8.25" opening, machined a 10" od mating surface for a ring to extend the bellhousing to the correct depth, and machined off the mount points while leaving their bases to add rigidity to the whole thing. It popped out of the vice at one point and machined off some metal that wasn't supposed to get machined off but that will get covered by the ring and weld and won't effect functionality.
After machining the bell housing I bolted it back to the engine and used a dial indicator mounted to the flywheel to check how off center the machine work was from the true centerline of the crank.
I machined a 10" od, 8.25" id, 1.78" thick ring out of a 10" square of 2" thick 6061t6 aluminum plate and drilled the borg warner bolt pattern into it. Using the runout measurement from the bellhousing I machined the outer edge on the side mating to the bellhousing that much smaller so I could mount it exactly at true center with the crank centerline. I tapped the holes on the back side so I could bolt it to the bellhousing to check/set center before giving it to the welder. I have a 6" spiral point pulley tap on the way so I can continue threading the holes all the way through for the transmission mounting bolts.