Best practice for drilling out snapped bolt

[AVI_8]

I’ve a bolt from an auxiliary belt tensioner which has snapped off in an engine block, steel bolt alloy engine, what’s the best way to drill it out?, I’m asking because I’ve not had much luck in the past with doing this.

Bolt is around 10mm diameter, I’ve got some cobalt bits and I’ve also bought a set of left hand drill bits made by Sealey, couldn’t find decent cobalt left hand drill bits, I’ve also got an easy out kit, bought a spring loaded centre punch as well for getting started.

To make it even more difficult I can’t see the area I’ll be working in, I can get a drill in but it’s too low down to see it without removing the bumper and rad pack, basically the complete front end in a 14 year old car.

I do have an endoscope which connects to my iPad so I’ve a descent enough screen size to hopefully get this job done, been putting it off for months now so I really need to get it done.

Should also say the bolt didn’t snap off during removal it happened in service, I’d fitted a complete new belt pulley and tensioner kit so I don’t know what the hell went wrong, the belt was fitted correctly, it’s a 2.0D BMW 116, there’s a round alloy positioning tang from the tensioner which also goes into the engine block and that’s snapped off flush with the block also, I can only surmise that the tang snapped off first allowing the tensioner to be stressed from side to side as the belt would be grabbing on and off snapping off its mounting bolt. Apologies for the long winded explanation.
Picture of the tensioner and the snapped off tang, what size drill bit should I start with, and then should I go up one size at a time? I don’t think the remnants of the bolt will be stuck in, it’s a new bolt and I probably used some copper grease when I fitted it, I can’t remember

 

[minimutly]

You are taking a big risk attacking this without eyballing it. If it goes wrong you'll need an engine. I would seriously consider front end off...
As for removing it I'm a big fan of centrepunch, small drill, bigger drill etc, then lh tap, hope it comes out, if not lh bolt, heat screw out. Easy outs are for ones that have snapped due to lack of tensile strength, if it's seized forget the easyout.

 

[addjunkie]

You are taking a big risk attacking this without eyballing it. If it goes wrong you'll need an engine. I would seriously consider front end off...
As for removing it I'm a big fan of centrepunch, small drill, bigger drill etc, then lh tap, hope it comes out, if not lh bolt, heat screw out. Easy outs are for ones that have snapped due to lack of tensile strength, if it's seized forget the easyout.

I concur….

 

[Kayos]

You are taking a big risk attacking this without eyballing it. If it goes wrong you'll need an engine. I would seriously consider front end off...
As for removing it I'm a big fan of centrepunch, small drill, bigger drill etc, then lh tap, hope it comes out, if not lh bolt, heat screw out. Easy outs are for ones that have snapped due to lack of tensile strength, if it's seized forget the easyout.

Agree with this, taking the bumper and rad off will seem easy compared to swapping the engine

 

[AVI_8]

You are taking a big risk attacking this without eyballing it

Yeh I know I’m trying to convince myself that I can get a good view with the endoscope and iPad, I’m probably kidding myself, just the thought of all of those snapping off fasteners

 

[8ob]

Would it be possible to fabricate and attach a drilling bush/jig/plate to a nearby bolt?It could take the guesswork out of the job.May be a few minutes well spent. Just thoughts

Bob

 

[AVI_8]

Would it be possible to fabricate and attach a drilling bush/jig/plate to a nearby bolt?It could take the guesswork out of the job.May be a few minutes well spent. Just thoughts

Bob

Could be Bob, I have a feeling that the bolt itself will unscrew fairly easily, it’s a new bolt, what you suggest could work for the tang when the bolt comes out.
Anyway I’m going to have a go at tomorrow very gently, whilst the car has been waiting for this to get done it’s decided to snap a coil spring which is conveniently pressing against the tyre (new springs fitted 2020 from ECP) so if it doesn’t look like it’s going to be sensible/easy by looking at it on camera I’ll just grind off the remnants of the spring, refit the wheel and get the car out of the garage until I’ve the time to do it the sensible way as I’ve more pressing car jobs to be done ATM the cars off the road just now and not needed at the moment anyway.

 

[welder_dave]

Check the one way clutch pulley on the alternator (assuming it has one) is not seized. When that happens it can stress the tensioner and may be a reason for your failure. Best of luck getting the broken bit out. Lots of patience and it will be fine.

 

[chrismac]

Would a left hand drill whip the bolt out or will it be tighter that that in its threaded hole,

 

[JOEPRO]

I always weld on a nut to remove any stuck bolt. The blast of heat helps too. 100% success rate at this stage I am experienced with it. I've had zero success drilling bolts out in the past unless you can get it into a drill press and well secured.

 

[mr haynes]

Have you stuck a magnet on it to see if it will unscrew?

 

[AVI_8]

Would a left hand drill whip the bolt out or will it be tighter that that in its threaded hole,

That’s the plan I’ve bought a set

Have you stuck a magnet on it to see if it will unscrew?

Haven’t tried anything yet.
I’ll let you all know tomorrow how it went, will go very gently as I definitely don’t want to snap a drill bit in the bolt

 

[Guzrik]

Heat it up with an induction heater.
Dremel cut a groove in for a screwdriver.
Acces would be handy for more future jobs? Maybe that would justify putting some time in to remove the front?

 

[minimutly]

I always weld on a nut to remove any stuck bolt. The blast of heat helps too. 100% success rate at this stage I am experienced with it. I've had zero success drilling bolts out in the past unless you can get it into a drill press and well secured.

I also like this method, especially in alloy. Weld a blob, then hold a bolt on it, weld blob to bolt. But ideally you need all round access with the mig...

 

[Erie Fred]

If you have access to a lathe, take a new bolt that can thread in or rod that is a slip fit in the hole, and drill
a concentric hole down thru it on the lathe.
use that as a drill bushing to make the drill in the center.
You can weld a scrap on the outer end as a lug to hold onto it.

 

[Farside]

To make it even more difficult I can’t see the area I’ll be working in, I can get a drill in but it’s too low down to see it without removing the bumper and rad pack, basically the complete front end in a 14 year old car.

I can think of no better method of effing it up.
Take the bits off.

 

[Gareth J]

If you think it's loose, Dremel a screwdriver slot. As mentioned. If it seized, weld attack if there is access. Again, if possible.

If you are going to drill it, with awful access, I would bank on it failing and you needing a fix. Might not be the worst thing, there's probably plenty of available material for a helicoil or timesert.

 

[Melvyn Best]

The best advice I can give is bin the easiouts!.. I’m not familiar with that model of car but I would try to gain access to the threaded end of the bolt and possibly cut a slot for a screw driver? Failing that ,if you have to drill it out drill from the threaded end ,if possible , using a normal drill bit, it may unscrew the remains? Do you have the broken section of the bolt and a new bolt? It might be worth comparing them side to side , if it’s only the threaded section that has sheared without any shank welding a nut onto the bolt and screwing it all the way through might work? A picture of the end of the bolt might help?

 

[GRW]

I tried to drill out sheared exhaust manifold bolts on my old Ford 2.5di engine in my elderly LDV Convoy (RIP).
Not easy to get at, no good line of sight.
It was a nightmare struggle, lots of hours, lots of fails, lots of frustration & cursing.

I strongly suspect removing the front will take less time & less stress than trying to fight with it from a poor attack position.

 

[bricol]

As others have said, bin the easy-outs now, before you snap one in something and make a relatively simple job even harder!

If the bolt isn't seized, or bottomed in the hole, it might come out simply from an off-centre levering/tapping with a centre punch, scriber etc.

If don't have the snapped off head of the bolt, have you looked in the hole to see if the remains are still there - that either the bolt fell out whole, or the remains have vibrated out in use?