Originally Posted by saltbob
the gear on starter only goes half way into flexplate I was thinking or a stock
flywheel could be wider or this may sound crazy thinking of two flexplates on trans Thanks
Pull the inspection cover off the bottom of the bell housing, using a good bright trouble light look in there. The flex plate will be stamped part that has among other features a pressed boss (actually several) for the torque converter mounting pads and bolts to interface with. The convex (outward facing boss) is to be toward the torque converter, the relieved side (concave) toward the engine. If there is a counter weight it needs to be on the engine side. So these are indicators that show the installation in orientated correctly without having to tear half the car apart to see things. While I don;t think this is your problem there are two Chevy starter and flexplate/flywheel combinations. There is a 153 tooth flex/fly at 12-3/4 inches in diameter which uses the starter with straight mounting bolts. There is the 168 tooth flex/fly that uses the angle mount starter.
You may want to remove the starter and check whether the solenoid throws the pinion all the way to the end of the shaft that being where it strikes a spacer that provides a stop between the pinion and the starter nose housing. The length of throw can be sometimes be adjusted a little with the thickness of this spacer. You'll have to look at the nose housing, some have a relief that the spacer goes into which prevents the gear from catching in the relief, some don't. For those that don't you can reduce the spacer's thickness as long as the gear teeth clear the housing when fully extended on the shaft.
Cracking of the flexplate is sometimes a problem, if the flexplate is cracked it will move around giving starter engagements from perfectly normal to very difficult and everything in the range between. Broken welds between the flexplate and ring gear will do the same thing.
If the tooth depth that's off in the top to base of the meshed gears (clearance) if too close the starter pinion can crash or miss engagement or even find it impossible to fully engage in the front to rear depth (longitudinal direction).
Another problem if using the older big motored starter is the lack of the brace between the back side of the motor and the block. These are always a pain to install and Corvette's raise the level of frustration by a power factor or two. But without this bracket the starter wants to twist on the two big mounting bolts which twists the pinion gear sideways in the ring, binding it before it gets full engagement.
Don't forget the heat shield, another PIA to install but important to the life of the solenoid.