Drilling out hardened broken bolts from engine block...drill sizes, types, speed?

[Daedalus]

I've done some searching and found some info, but haven't gotten all the answers.

I have a coupe broken bolts in an engine I bought. They are below flush, and I honestly don't have the skills to weld anything here. I've been going at it with some cheap 7/64" Ti-coated drill bits just to get the holes started, but these bits don't do much damage before they're done. I'm OK buying better bits if they'll last longer. I'm using Tap Magic cutting oil. I assume the bolts are somewhat hardened, at least grade 8. Guessing 1 is 1/4" and the other is 5/16", or maybe #10 and 1/4"? I haven't put a caliper up to them.

Am I being too aggressive with drill size? Should I start smaller?
What RPMs should I be drilling with, and for what diameter drills?
Any recos on drill bits? I see some Cobalt bits on Amazon, not many carbide bits. Would prefer to buy multiples of the same size, rather than have a set of different sizes. For most jobs I can usually get by with the cheap gold Ti bits I buy in bulk.
Is there a better cutting fluid to use?
Any other advice?

 

[Sumboodie]

Grade 8 bolts usually drill fairly easy.

 

[BTL-A4]

Get a reverse drill bit. As you drill, it might back the bolt out. I put the hand drill on the low speed/higher torques setting and go slower.

 

[teagueo]

Use Cobalt if drilling by hand - carbide is brittle and will snap easier. Like @BTL-A4 said, left handed bits will help back out the bolts sometimes.

You can get better quality drill bits at McMaster vs Amazon, and next day shipping.

Also, start with a center drill if you can. That will help get your pilot hole started.

 

[dogdog]

What is a jobber drill used for?




A regular jobber bit is best used in softer materials such as wood, composite, and soft metals. For harder materials and hard metal drilling, a mechanics length drill bit is recommended as they are a stronger bit. Jobber length drill bits are the most common and popular type of drill bits.Sep 15, 2017

Don't get too hang up on the brand and coatings.... they are helpful but doesn't make the drill. Its a coating. Nitrate, cobalt, seamen, or what ever.

or use a starter bit and start from 1/8 then move up to about 1/4 and use your favorite extractor.


I always like the tips from this guy on drilling out bolts, other than from those machinist guys. Not too bad tips. he got a few other videos on drilling out bolts.

 

[Jswain]

How much are you drilling before the bit is "done". If it ain't drilling then stop. You may need to take a carbide burr and get below the surface then re approach with a drill bit.

Are the bolts in the head or block or?

 

[Wamsutta]

I'd get an American made cobalt bit and drill slow. Your cutting oil is fine.

 

[Retired dozer fixer]

SLOW and steady is the key. Your oil is good too

 

[OccupantRJ]

Carbide can be used in a hand drill, but get a carbide tipped drill, not solid carbide. The steel shank is more forgiving in hand use. I used these in die work occasionally. They will be in a machinist catalog like MSC Or Travers.

 

[Leaflessshadetree]

Short 1/8" bit. Drill speed slow enough to produce chips or spirals.

 

[cherrybomb]

Slow and steady,this is one example where a good quality left handed direction drill bit with the tap magic will get the job done.Start by center punching carefully. I'd start with about a 1/8 bit,and move up.The closer you got to center,lets you move up to the larger bits without getting to close to threads.I would have two of the last size left drills you figure will work.As you move up in size,removing more material without damaging threads,this is where the left hand rotation drill bits start to really help.I keep my lefts in a hard glasses case,clearly marked,,away from regular bits.Pricey but when you need them??? Fastenall has them

 

[Renegade1LI]

Get the ridgid model 10 extractor set, probably the best one out there, I think it gets rebranded for SO.

https://www.amazon.com/RIDGID-35585-Extractor-4-inch-2-inch/dp/B000WQYJIG?tag=atomicindus08-20

 

[rust in the eye]

I deal with this more than I care to. What works for me is sloow speed, as much pressure as you can apply*, a sharp bit with plenty oil.
Centering is important, if you miss center sometimes you can walk the drill a bit by going at an angle for a bit then straightening up. Depending on the size of the fastener you might want to start with a smaller bit first. I try to cut all in one go(up to 3/8") as when stepping up I find the bits sometimes grab when enlarging a smaller hole. I'll use a bit just smaller then the root diameter of the fastener. Often you'll be able to get out the threads of the old bolt without too much drama.
Left hand drill bits serve me about as well as a slot machine. In Automotive situations a broken fastener is usually due to to rust, no left hand drill will break that bond. Nor will easy-outs, break either in the hole and you're up **** creek. I've broken both and would rather have venerial disease.
* I mean as much as you can, I'll sometimes have a bruise on my chest from where I've been bearing down my weight on a hand drill. Drill slow enough for curls and you're cutting well, chips? slow down and add pressure. Overheating ruins bits so keep it slow and plenty of oil.

Did I mention slow and loads of pressure??

 

[JradM]

If the bolt is protruding at all, I run a file across what's left to get a flat surface to drill into - otherwise the jagged break area causes my bit to walk. If it's below the surface, I try to use a carbide burr to dish the center slightly.

 

[richfinn]

An optical centre punch is very useful if you have space, exhaust studs particularly can be very hard to drill, go slow and use sharp bits.

 

[isr2kba]

If a brand new bit isn’t doing much damage it may be because you’re drilling wrong or

Someone else tried before you and broke something off in there or

The engine you just bought is an outboard and the broken bolt is stainless steel or

Some other reason.

If it’s none of these, then take heart and listen to all the advice above (throw a coin on the ccw conflict — that works way less than half the time for me and I’m always using LH drills).

Patience and time are your assets because this is a HARD job.

 

[Blueshound_GJ]

At my shop we had a rule that if it was broken off flush or lower in the head or block, it automatically got pulled out of the vehicle and sent to machine shop for extraction. Too many wasted hours and broken drill bits, all to send it out anyway.

 

[TopFuel]

An optical centre punch is very useful if you have space, exhaust studs particularly can be very hard to drill, go slow and use sharp bits.

Thank you for bringing this type of punch to my attention. I've always used a spring punch and the optical punch looks great.

 

[PMD1966]

Get a reverse drill bit. As you drill, it might back the bolt out. I put the hand drill on the low speed/higher torques setting and go slower.

Cobalt reverse drill bits usually work for me.

 

[Daedalus]

Thanks everyone for the replies. An update: After posting I received a dozen same-day shipping cobalt drill bits from Amazon. I also ordered LH drill bits, but those were not available same-day, and should be here later today. Before posting, with the cheap Ti coated bits I burned through 3 of them rather quickly, and only got about 1/8-3/16 deep. I slowed the drilling down to about 150 RPMs and used 2 cobalt bits to get another 5/16" deep or so, so the cobalt bits are definitely holding up better. I'm going to wait until I get the LH drill bits before hitting it again. Goal is to open up the hole to 5/32 and give it a try with my Hanson extractor.

 

[rust in the eye]

Sounds like you are working on an 1/8" hole here. Not sure what you're drilling into but that should be no challenge in anything I've found on cars so far.
MORE PRESSURE

 

[richfinn]

Thank you for bringing this type of punch to my attention. I've always used a spring punch and the optical punch looks great.

You would need the space for it obviously as it's really a lay out tool, but would work well with the engine out and manifolds off etc.

 

[cherrybomb]

Sounds like you are working on an 1/8" hole here. Not sure what you're drilling into but that should be no challenge in anything I've found on cars so far.
MORE PRESSURE

Yup,more pressure should yield a much better looking thicker chip

 

[Renegade1LI]

Thanks everyone for the replies. An update: After posting I received a dozen same-day shipping cobalt drill bits from Amazon. I also ordered LH drill bits, but those were not available same-day, and should be here later today. Before posting, with the cheap Ti coated bits I burned through 3 of them rather quickly, and only got about 1/8-3/16 deep. I slowed the drilling down to about 150 RPMs and used 2 cobalt bits to get another 5/16" deep or so, so the cobalt bits are definitely holding up better. I'm going to wait until I get the LH drill bits before hitting it again. Goal is to open up the hole to 5/32 and give it a try with my Hanson extractor.

Try not to use a tapered extractor, they tend to expand the bolt, use a straight flutted type.

 

[Steve_P]

Grade 8 bolt isn't very hard, Rc 33-39. Despite half? the posts here, you don't need a cobalt bit to drill this, just a high quality bit. Norseman Magnum is superior to cobalt bits for an application like this- according to Norseman.

 

[teagueo]

He said it was a hardened bolt, AT LEAST grade 8. If I didn't want to **** around, I'd use Cobalt bits. Dimple the bolt with a carbide burr like mentioned previously if it's a rough break surface.

Start with this center drill:

McMaster-Carr

McMaster-Carr is the complete source for your plant with over 595,000 products. 98% of products ordered ship from stock and deliver same or next day.

www.mcmaster.com

Drill a pilot hole with a stubby length drill:

McMaster-Carr

McMaster-Carr is the complete source for your plant with over 595,000 products. 98% of products ordered ship from stock and deliver same or next day.

www.mcmaster.com

Then use your extractor of choice. Penetrating fluid wouldn't hurt either...

 

[Daedalus]

Thanks for all the help. Finally got to the job today. I took my time and didn't rush it, and things worked well without having to feed the swear jar. The cobalt bits made a huge difference; I'm not sure I've ever used them, but I will keep them handy in the future for sure. The LH drill bits didn't get the bolts moving this time, even with a spritz of Liquid Wrench.

I wrapped a neodymium magnet with a paper towel and stuck it below each bolt before drilling. Helped keep chips in place, except for 1 freaking chip that got flung off the drill bit and unbelievably landed in an intake port above and to the left! Luckily the valves were closed and I was able to fish it out with a magnet. I wasn't even certain I saw what I thought I saw, until what I thought I saw came out stuck to the magnet. I covered all the ports after that!

 

[LopezBart]

I covered all the ports after that!

Blue masking tape can prevent a lot of swearing...