Brumbach

What type drill bit should I be using to cut into the remaining bolt? Bolt is broken off deep inside of the block. BTW, I'm using heat and penetrating oil. It's really stuck so I've got to get the extractor deep enough inside of the bolt to turn it. The tip of the bits I've used so far can't stand up to the hardness of the bolt.

Thanks,

midyearvette

titanium tipped bits are about all you can use .....if the bolt is 3/8 i would strive to go up to 1/4 inch for a good size easy out as not to break it inside the bolt......

JoeCool66

I’ve had good luck drilling into broken bolts using Left Handed Drill Bits (reverse thread). Sometimes if you’re really lucky, you don’t need the extractor because the bit catches what’s left of the bolt and screws it out. Doing it slow is the key. They do sell special hardened drill bits you would use to drill out a broken thread tap but I would think you wouldn’t need that just to remove a WP bolt.

Joe

Scott Marzahl

I've used Cobalt bits with good success, they are brittle so don't bend it or it will snap. Regardles if its HSS, Ti or Cobalt, make sure its a new QUALITY bit and not a POS from Harbor Frieght. Try to center punch it too so the bit starts in the center. I just had this happen on a Subaru last month, and I have some reverse drill bits for this kind of stuff. Fortunately after a minute of drilling with a reverse bit the broken bolt spun out.

kskid

I have always used Aero Kroil spray. It likes eats rust. Sometimes it is hard to find. Ordered mine from Kano Laboratories.

6D2148

small amount of heat and shove a candle in there , the wax will wick in to the threads and free it up

MikeM

If it was me.....................

I'd get a drill bit that was just touching the original 3/8" threads and run it in as deep as I needed to go. Then, I'd carefully run a coarse 3/8" tap in the hole and the tap will remove the old bolt plus re-establish new threads.

If you screw up, just use the O/S heli coil bit, drill O/S and install the heli coil.

65specialk

First thing, dont heat it red hot as it will be so hard you wont be able to drill it. You want to heat it just enough to break the bond. Let it cool completely then drill. Do not drill a hot bolt. Good luck. Dave

Plasticman

Another option is a diamond bit in a Dremel tool (and a steady hand). Remove the center bolt material just shy of the threads, and then peel the threads out.

Plasticman

Westlotorn

I agree, I would make sure it is a brand new drill bit, a good one sharp as you can get. You get one chance to fix it fast with your drill and tap method. If it buggers up the good advice given on a heli coil will get you back in business.
On really hard steel, hard plate type metal the Rodman Bits will cut through but they are very slow and don't work worth a bean on softer steel. They seem to chip away rather than cut.
A buddy with a Safe business talked me into buying a set of the Rodmans. Sometimes they save you.

Gettysburg

Years back my Street Rod had a bolt break off inside the block. (custom alt. and AC bracket bolts were too long and bottomed out inside the block). Always being leary of being able to center punch at dead center, I took an identical size bolt and had my machine shop buddy drill out the center of that bolt as large as he could without destroying the outside threads. Screwed it into the hole against the broken bolt and simply drilled slowly and the old bolt disintegrated. Still have that puppy in my tool box to this day.

Tampa Jerry

I had a Nissan and broke a water pump bolt deep in the block. My dad made a busing that fit the diameter of the hole and drilled out the inside so we could drill and tap the hole. It was blind all the way and the bolt backed up to a water jacket. I also saved the bushing. We had to use a 5" tap. We ground the nose off the tap to make it a bottom tap. The engine lasted another 75K miles. Did I mention we broke an easy out in the block The whole job took about 5 hours of making bushings and finding oddball taps. Good luck. Jerry