05-07-2020, 12:26 AM
I had a precisely similar problem with one manifold stud on my car. One stud blew out of the block. I discovered that someone previously had drilled it out off centre, but only after I had helicoiled it! So I drilled the manifold holes out to 9mm, which was the only drill bit that was big enough and sharp enough. The extra clearance in the holes was sufficient to allow the manifold to go on without binding on the studs.