HELP! broke off a Grade-8 bolt inside my block, What drill bit do I buy to remove it?

Thanks everyone for all the great advice, it looks as if I'll have a lot of research to do this week in choosing my best option for removing the broken stud. Given that I have very limited knowledge in this area, I'll more then likely be taking the engine to a trusted local machine shop or one of the experienced tig welders here in town that I trust to get the job done.

 

Have you thought about contacting John Coffey?

 

The machinist I use , would take a flame shaped carbide cutter, (probablly 1/4 inch dia) and carefully cut it into the center of the bolt . I immagine it would be best to use a center punch to try to remove or break the bit. He would carefully grind the center out of the bolt, then use a pick to pull the threads loose enough to grab with some needle nose pliers. I always use this method when an easy out fails. It works.

 

looks like the bit you broke off was small, 1/8 inch or less. everybody wants to start off small and work up to the next size larger. it's a whole lot easier to snap a smaller bit. here's a tip for next time, especially in a case like yours where the bolt appears to be broken off below the surface.
find a piece of steel tubing that fits in the hole snug like brake line. then start the largest bit that fits the ID of the tubing. the tubing acts as a pilot to keep the bit centered. at the very least, it dimples the broken bolt making it easier to start a slightly smaller bit. i try to stay away from anything smaller than a 3/16.
i've also had good luck with the left twist bits.

 

I've done something similar on a SBC that I broke off a pulley bolt in the front of the block. I made up an aluminum plate with a larger hole, that was bolted to the front of the block. Then I made up a series of mild steel quick-n-dirty drill bushings.

Mine didn't have the broken drill, I used mine to step up the drill sizes to the point where I could pull the remnants of the broken bolt threads out. The concept is the same if you have a decent shop around that can do it.

Bob

 

I'm liking the tubing trick, use what you have on hand. Another one I've used, if you have some thread left in the hole and can screw something into it (even 2 threads), take a allen head screw (cap screws will work too), drill a pilot hole through it (lathe required) and you have your drill bushing. Make up a series of them as needed.

Bob

 

same basic principle as your idea. i just like to get away from using too small of a bit that is prone to breakage.

 

Anything less than an 1/8" drill is just asking for trouble. I like to start with the 1/8" since I probably have a real drill bushing for it and I always have a shitload of either TiN coated or carbide drills on hand.

Bob

 

Yep- Never try to beat a man at his own game!

 

Just a F.W.I.W. None of the timing covers bolt holes the OP is using are blind. The two lowest go into the crankcase area, the two uppers go into the water jackets. They can easily be taken to 3/8 or even 7/16". (Just remember that the cylinder walls are behind those two upper bolts, and use the correct length, especially on the drivers side.) At that point, it is just a matter of drilling the timing cover bolt holes and the mount holes to match.

 

Looks like you have made the right decision to me, let the pros have at it, it wont be all that expensive.

 

Yep! When it come to heliarc welding there's no one I trust more then John. If I decide to go the welding route to get the bolt removed, the motor will go to John to get the work done.

 

I thought he meant the John Coffey from the Longest Mile, with the flys coming out his mouth. I'm sure he could fix it.

 

ok backyard engineers that think bigger is always better

I used to sell fasteners for a living

a 5/16 grade 8 bolt has over 7000 pounds of tensile strength
a grade 5 has over 6000
so before you start drilling look at the application

 

Six years later .... @Payne .... what did you do ??

Yup' .... broke a bolt flush. Great reading thus far ! Dumped about 30 bucks in bits already. Fun fun !

Trying to get it deep enough to use my left handed bits.

 

Cobalt screw machine length, lots of pressure and slow speed.

 

Hey @kidcampbell71, I went through this last summer, and like you I got nowhere with drill bits. I wound up using Snap-On mini carbide burrs on a dremmel to bore a hole, then eased it out with a good-quallity extractor.







You can visit my build thread to relive the entire aggravating experience, starting with post #504
https://www.jalopyjournal.com/forum...out-of-the-weeds—build-thread.1003005/page-17

Not my finest hour, but got it done!

 

Ya figure he is still working on it.......................????

 

Kidcampbel171 is. See his post above, from this morning.

 

Ha. Yeah I remember that thread. I drilled thru some stainless 303 rod that I made into drill guides to ease out a broken head bolt .... without removing the SBC heads ... on your broken bolt thread .... but I'll be damned if I can drill this f#cking FORD bolt thru. Kryptonite grade 15 ??

I have the Irwin Hansen kit you have ... along with a left hand drill set .... but looks like I may be going to buy some mini carbide burrs now.

 

I didn't go back to this threads' start and I'm sure this was mentioned already but a left hand drill bit works well with low rpm and a fair amount of pressure, remember your not drilling but trying to spiral the bolt out by getting the bit to dig in.
After center punching; use a center drill first to get the drill bit started on center, wouldn't hurt to first give it a good squirt of PB Blaster (penetrating oil).

 

Take it to a shop with a torchman who has done this before.
I described this in one of my previous posts.
I haven't drilled out a stud for years or the last time it didn't work.
Fireball 5

 

@TR Waters said that those holes aren't blind, so using the torch method will end up with all the slag remnants in the crank case. Not a big deal on a bare block, the OP said that the engine is finished and running. I don't want torch blast and bolt remnants in there. Might work for @kidcampbell71 though.

 

That Rescue Bit seems like the best option.

 

Try annealing the bolt if it's too hard to drill. Using a small welding tip in a torch, heat the bolt to cherry red and slowly back the torch away to allow the bolt to cool very slowly. It will soften it enough to drill it.

 

I'd take Engine man's approach to hardened material of annealing first. I've found a Bernsomatic butane Micro Torch works well for heating small small things cherry red when I was afraid to damage surrounding areas with my full size O/A torch set up, also much handier to work with in tight areas. My Hanson 10 piece extractor and drill set #11119 with left handed cobalt drills has bailed me out many times, quite often the left hand drills buzzing the broken off piece out without having to go to the extractor. Just remember to reverse the drill motor first, don't ask how I know.........

Ed

 

To revisit tips and help ... revealed within this thread .... annealed broken bolt with torch. Cherry red, cooled, cherry red, and cooled again.

Got through said bolt. Carbide tipped TILE/MASONARY drill bit. 3 of them.

Finally.

Left handed bits walked the rest of the mangled bolt out.





So in short ..... cobalt bits >> failure for me. Cobalt left handed bits >> failure again --- broke 2 of those sob's !! Titanium coated bits >>meh' ... penetration to dull end, then stepped up in size to same result ..... but gained each time ... until ...

Torch and carbide masonary bits !!! Who knew ?? Guess you guys did. Thanks OP. Thanks HAMB. Only took me one day.

Now off to drill oversize ....and retap !!

 

Mason bit has flat side cutting edges. My late shop foreman in the decades past, tought me to grind a regular bit to have straight cutting edges to go through nasty broken exhaust bolts on State Highway 477 Ford gas powered plow trucks. Those manifolds ran true red color when pushing deep snows, and the bolts would break when we had to replaced burned/cracked/warped manifolds.

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