lightskindwonder

Upon torquing my rear-most passenger side intake manifold bolt, the bolt head completely broke off (i know my dumb @$$ misread 71 in-lb for 71 ft-lb). The bolt shaft broke just flush with the head (just below the manifold flange). After trying and breaking a few titanium drill bits and 1 cobalt drill bit, I'm beginning to think nothing will get this bolt out of the head. I've only managed to make a small surface dent in the center of the bolt even after constant pressure and drilling. I'm almost thinking about leaving it and hoping for the best...but I know a leak will spring up from it. Does anyone know which type of drill bit should be able to drill through this grade 8 bolt so that I can use some sort of easy out tool? I have the speed of the drill at the highest setting, around 3k rpm, and still no luck getting the bit to drill a hole. Would trying a 3/8 bit be a possibility? Simply try to drill out the whole bolt and hole, then re-thread the head using heli-coil or something? Would some sort of cutting oil help the drilling process? Any help is greatly appreciated.

bombebomb

I don't really think I am mechanically inclined to give advice on something like this, but I wish you the best of luck. Breaking bolts off is always a nitemare, we typically drill them out but you seem to have tried that.

MikeGyver

Any quality drill material will easily cut grade 8. Hss, black oxide, titanium nitride, cobalt. You might be overspinning the bit, that'll just cause excess heat and instantly re-temper and destroy the cutting edge. Make sure you use cutting fluid to help control the heat. The harder you can push the better. Using a left hand twist drill bit is always a good idea too.

Personally, I'd pull the manifold off, weld something shaped like a box end wrench to the bolt and just unscrew it. TIG weld if possible, if not, MIG weld making sure to put the heat on the bolt head and letting the puddle work its way over to the metal piece for best fusion.

shoebox

You don't drill metal with high speed. You use low speed (and a very sharp and lubricated bit).