I recently stripped the threads in the snout of my 4.8L LR4 engine crankshaft. I believe it’s the same diameter hole as an LS1, LM7, etc.
Anyway, the hole is exactly 18.0mm inside. I didn’t want to try to drill the hole any bigger, as I didn’t trust myself hand-holding a drill straight enough. So, I started looking for other options.
Turns out the M20-2.5 tap requires:
17.5mm drill hole for soft metals like Aluminum
18.5mm drill hole for hard materials like Stainless.
Since the steel of the crank snout is relatively soft (certainly not as hard as Stainless), I thought I’d give it a go.