350 Starter holes drilled incorrectly?

[Gibson]

Ok, got off the phone with Powermaster (really nice folks) the model I have looks to be a white label version of one of their starters - possibly an older model. At any rate, they helped me anyway which I thought was cool.

They have seen this issue before on sbc's and confirmed that it is very possibly just a case of stacking tolerances. So my block is off a fraction, the crank might be off a fraction, etc. All those add up to "too much gap between the starter mounting holes and flexplate". The tech said that on a gear reduction starter, you really only want the teeth to engage about half of the width of the flexplate, so I don't need a ton more throw really. Unfortunately there is no shim of the type Desert mentioned available for this starter.

What I'm thinking of doing instead is modifying the pinion gear on the starter. On the one I have, there is at least a half inch of smooth bushing area on the tip of the gear. You can see that in the pictures - it is pretty large. I'm going to precisely cut a thin disc of that away and move it to the back side of the gear, effectively moving the teeth forward about 3/16. Whats the worst that could happen, right?

[Gibson]

Well, it is confirmed. Stacking tolerances (and possibly a bur or some debris) seem to be at the root of this problem.

I was fortunate enough to get some help from a long time mechanic and auto vocational teacher tonight. He confirmed that the flexplate looked correct, as did the mate between crank and flexplate and block and bellhousing. Also he checked the converter clearance, and it was within spec. After torquing down the blots on the converter, there was no shift in the flexplate location. I now suspect there might have been a piece of trash or something where the converter mates up which was part of the cause of the excessive flexplate runout (the gap between starter and flexplate is STILL on the large side, but not as bad as it was when the flexplate was bolted up before)

Tonight we mounted an OEM style starter which appears to have enough throw for proper engagement. Gradys was right about modifying the gear - that won't work. The flange on the back is what the thrust bearing/fork thingy pushes against. Instead, I will go with what Powermaster support suggested and machine the body of the starter a bit. It would still need to be modified to work properly.

For now, I'm just going to enjoy being able to start it with the OEM style starter!

Thanks to everyone for the help! If someone runs into this in the future and has this same problem, I would recommend they first unbolt the converter from the flexplate, ensure proper converter/flexplate clearances, and torque things back down to spec and see where they are. Also, try an OEM style starter first and make sure the problem still exists.