Broken bolt in block under throttle body adapter - what now ?

Buy a new engine ?

I'm in the process of putting the bike back together after changing out the cams.

Go to torque down the throttle body adapter boots (pair of 8mm flange bolts to each) to the manual-stated 12 Nm, and broke the head off one of the bolts, about 3 mm into the block.

I have screw extractors, left hand drills -- never used 'em, and quite nervous doing anything like this on the engine block.

Please advise.

Thank you.

If you are not comfortable with extracting the broken bolt look around your area for a mechanic, engine building shop or machinist that can do it.. It is a pretty straight forward job. Even if they have to drill out the block it should be easy enough to put a helicoil in there. This is actually nothing more than a not quite major but more than minor inconvenience. It's easy enough to fix.

bob

Joesmoe said:

Buy a new engine ?

I'm in the process of putting the bike back together after changing out the cams.

Go to torque down the throttle body adapter boots (pair of 8mm flange bolts to each) to the manual-stated 12 Nm, and broke the head off one of the bolts, about 3 mm into the block.

I have screw extractors, left hand drills -- never used 'em, and quite nervous doing anything like this on the engine block.

Please advise.

Thank you.

Click to expand...

If you have a mig welder I would get a nut of the corresponding thread size and pool some weld into the hole,the heat from the weld will usually free the broken stud and hopefully with the nut welded to the stud will then wound out. Plenty of tutorials on YouTube,just be patient and good luck.

I have removed many a broken bolt and stripped bolts. Start out with a very small drill bit and increase in size until you get close to bolt size. Then use a exacter. Not hard to do just insure you drill straight. Had to do this recently with front brake retainers.

Firstly Paul , don't be tempted to use the stud extractors , break one of them in there and you will have a problem ! I have dealt with this on many occasions and have not had to resort to any more than a bit of patience . Firstly if you have no stud above the hole to grab , you will need a good quality , sharp centre punch . Not a spring loaded self punching one but a quality old school style . Hold the point as near as possible to the centre of the broken stud and give the punch a good clout . Just one mind , don't be tempted to hit it again . You should now have a punch mark in the centre , or pretty close in the stud . Next use a very sharp quality drill bit , around 2 to 2.5 mm . Before you start , put the drill bit down one of the other holes that you have removed a stud from and Mark the bit with a blob of paint or tape . This will give you your drill depth . Then gently drill the stud after entering in the pop mark . Don't push , let the drill do the work and every now and again check you are drillings square . Once drilled to depth , go up a size or two and drill again . Keep repeating . If you haven't drilled perfectly centre , just check that the drill bit isn't encroaching on the side of the hole . Once you have drilled the majority of the centre of the stud out , use the centre punch or sharp pick to cave the stud in towards the centre . This will break it out of the threads and give you a purchase with needle nose pliers . Et voila . A bit of patience and judicious picking and the stud will yield ! I must reiterate tho . The centre punch mark needs to be as close as humanly possible to the centre of the broken stud ! Hope this helps ?

Very descriptive. I do use a extractor when possible but do not use a lot of force. If it does not move we follow the same as you described. Nicely written.

A HUGE help gentlemen !

Quick question, I have a set of left hand drill bits, 1/16th on up.

Would that be useful ?

Paul,

Im a machinist......a picture please of the offending object?

From your description, the bolt is approx .118 recessed. Id make a drill bushing. This will do 2 things, keep you on center and perpendicular to the work.

The best advice I can offer is think before you drill!

Joesmoe said:

A HUGE help gentlemen !

Quick question, I have a set of left hand drill bits, 1/16th on up.

Would that be useful ?

Click to expand...

Yes, once your ready to drill, every now and then, like winning the lottery the offending object spins itself right out! When that happens, do a little dance and know that this will be a very good day!

sonny said:

Very descriptive. I do use a extractor when possible but do not use a lot of force. If it does not move we follow the same as you described. Nicely written.

Click to expand...

I agree , extractors have their place . But you being a metal worker will know full well , there are extractors and then there are extractors . When most home mechanics equip , they would not want to spend the money that a really good quality set would cost , or even know where to buy the best . Cheaper ones shatter unexpectedly and if that happens , one needs to be looking for a firm who specialise in spark erosion !