17/64 not working can I go to 9/32???
 

I'm drilling out my exhaust studs but the threads are not coming out. Can I go to a 9/32 drill bit or will that take out the cylinder threads.

The tap drill for an M8-1.25 thread is 6.8mm. A 9/32" drill (7.14mm) would produce a slightly oversize hole for proper M8 threads. If the drilled hole is relatively straight, I'd consider using the 6.8mm drill, then run the M8 tap into it. If you can find a left-handed 6.8m drill, the CC cutting direction may help dislodge remnants of the stud in preparation for rethreading.

Sherwood

Thank you. I may have to order some helicoils. Boo

Someone - Stomski? Sherwood? - makes a jig to use when drilling out head exhaust studs. I haven't had to do this yet, but I'd buy the jig if I was going to do so. Drilling a concentric hole is very hard with a hand drill motor. Hard enough to get it started in the exact center, and harder still to have it lined up exactly along the axis. I bet you are not using a drill press or milling machine to do this. - you have the engine on a stand, no?

Something to consider.

I don't see Helicoils as the end of the world for something like this. The studs don't take all that much strain. These aren't rod bolts, or even case perimeter bolts. Everyone ought to own the drills, taps, tool, and a handful of inserts for 8x1.25.

Sorry Walt, not I.

Sherwood

I had a snapped exhaust stud when I first bought the car (way before I decided to pull the engine out for the EFI project) - we tried drilling it out but unsuccessfully, albeit with a homemade version of the drilling jig that Walt mentions (and I'll point out, probably nowhere near as good as the Stromski (?) version, but all we could do in the time we had).

We ended up getting the car - now without exhaust system on it - about a mile down the road to a classic motorbike resto shop....and there's a guy there who is "Mr Stud Removal"...apparently spends a lot of time working on Ferrari's, which are prone to these sort of issues.

Anyway, he got it out (I wasnt there, can't say how he did it) but our fallback plan was to have it spark eroded out.