Small diameter bolt broken off below surface - suggestions please

Working on the engine of the spare "donor" bike for my SO LS650. I removed
head cover but one bolt broke off about 5 to 7mm below the surface of the
mating face on the cylinder head that the head cover bolts on to. I reckon
there may be 15 to 20 mm of bolt left in the hole. It is an M6 bolt so the
hole doesn't leave much room. I need to be careful because I don't want to
scratch the mating surface around the hole. If all else fails I should be
able to drill it out and helicoil it but I want to avoid that if possible.
My current plan is to get some left hand drill bits and try to drill it out,
starting with a smaller diameter bit and working up in diameter, hoping that
it will free off due to heat, vibration and anticlockwise drill rotation
before the threads in the head get damaged. Any better ideas?

 

Plan A sounds feasible. Plenty of Plus Gas etc will help.
Can you get any reasonable heat to it to assist the removal?

 

Using the patented Mavis Beacon "Hunt&Peck" Technique, TMack

Sounds good to me. If you can get a centre punch down to the stub first,
even more betterer.

--
Wicked Uncle Nigel - Podium Placed Ducati Race Engineer as featured in
Performance Bikes and Fast Bikes

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Where are you?

I've got a special tool to fix this exact problem, it's a short LH drill tip
with an expanding collar.
The tip drills into the core of the stud, which is sometimes enough to do
the job anyway, then the collar feeds into the hole and locks, so the torque
of the drill forces the stud out.

This widget cost $35 from the US should be treated with some care but,
though it's only meant for 6mm studs, I've used it successfully for 8mm and
even 10mm...

 

You'd be in a better position if the head is mounted solidly in a drill
press. Going at it wth a hand held drill is going to be a difficult
proposition.


--
Beav

VN 750
Zed 1000
OMF# 19

 

10 minutes work with a small pin punch, a scriber and a 1/2 lb hammer.

Just make a small punch mark on the edge of the broken bolt and then
turn it out by hand. Works for me.