left hand drill bits

[Greig Smith]

bought a cheap UK Sealey set to start, and punched the centre of the two manifold studs. Feel soft enough. Realised that the LH drills are quite flat ended, so am going to have to open the hole out a good deal at shallow depth before the 3mm one will actually catch and stay central. So I see one does need them from 1mm upward to start applying the correct turning force from the beginning.

Center punch the broken studs as accurately as possible, start the initial drilling with your conventional RHD drill bits and as soon as you have a suitable pilot hole, switch over to the LHD bits & run your battery drill in reverse.

Aye
Greig

[JonE]

ok, done as above and that worked well, but LHD 3mm has moved sideways in pilot a bit so definitely slightly off centre now.
Shall I bolt a manifold in place and use that as a guide as I go in with the next size up?

[Greig Smith]

Probably a good idea Jon, just use it as a simple guide

Aye
Greig

[David Stepney]

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.