Are there different sizes for flathead transmission bolts? I have a 59a motor with 7/16 threads in the block and sump, but the bolts won't fit through the bellhousing. I've tried my NOS Flathead to Lasalle adapter, stock 39 box, and a homemade adapter. All of them are smaller. What's going on here? It's easy enough for me to open the holes, but why would they not fit in the first place.
Every one I ever worked on had 3/8 threads. Perhaps someone drilled and tapped yours oversize. I'm also thinking there won't be alot of room for the 5/8 heads on those 7/16 bolts. You might think about heli-coil inserts and go back to 3/8.
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