Technical 235 Chevy timing cover modification

I want to change the bottom bolts (which come in from inside the oil pan) to external bolts, but I keep reading articles which say to drill and tap the bearing cap to take a 5/16" bolt- but the hole is already 5/16" diameter- too big to tap a 5/16" thread into. The only way I can see is to drill and tap for a 3/8" bolt. Then I would drill a suitable clearance hole to open up the existing (tapped) holes in the re-enforcing block to clear a 3/8" bolt. Am I missing something?

 

I remember dropping the pan on my 235 to tighten them. Put it back together, a day or two later I wondered why I didn't tack weld them to the plate if they ever needed tightening again. Mine was seeping oil from the bottom of the cover.

Wouldn’t help with having to drop the pan to replace the cover gasket, etc. though.

 

You're not missing anything. That's exactly what I did on my engine.

 

A 21/64” (1/64” over 5/16”) pilot hole is what’s required to tap for a 5/16” Helicoil.

 

Yes. That's all you have to do. Tap for 3/8-16 & drill a clearance hole in the "re-enforcing block". Pretty standard modification for these engines.

 

All mine are tapped for 3/8”. Best to use what some call a “header” bolt. Built in washer and a 3/8” head for ease of attaching.