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dwsonar

need help re: broken bolt

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dwsonar

Not motorcycle, but still need help. Yamaha outboard, Have three broken head bolts. Hardened bolts, two broken below the surface.
What kind of drill bits do I need? Any easyouts better or worse than others? I feel like I only get one chance at this, and need to get it right.

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Believer45

Do the bolts go into aluminum threads?  Are the bolts grade 8 or stainless steel?  The kinds of metal you are dealing with can have an effect on the method.

 

I would suggest getting reverse twist drill bits, they turn the opposite direction when drilling so the "urge" of the drill will be to unscrew the remainder of the bolt rather than screw it in tighter.  Start with a smaller bit than you need and drill a pilot hole then follow with larger bits so you can avoid damaging the threads.  As for what kind of bit, I have used titanium coated bits on harder metals but you may have a hard time finding them in reverse twist.

 

You are right about one chance, if the easy-out breaks off in the bolt it is a problem.

 

Once the drilling is done and you are preparing to try to remove the bolt, an old-timer trick I have used that frequently helps is to warm the bolt and surrounding metal (not hot, just warm enough - maybe a couple hundred degrees) and apply candle wax.  The wax will be drawn down into the threads like solder will draw into a copper joint and can help freeing up the stub of the bolt.

 

If you are not successful, you can repair damaged threads with helicoils - they will work on head bolt threads just like anywhere else.  I have used them on semi-truck diesel engine head bolt holes, exhaust manifold bolt holes and many less stressed locations.

 

Be patient and good luck with it.

 

Dave / Believer45

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dwsonar

yep, grade 8, aluminum block.

What drill bit would you recommend?

 

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OnaWingandaPrayer

I am not sure what type drill bit to use. Left Hand twist and drill in reverse is a great idea if available.

Another thing I would try ,is bolt the head back in place with remaining bolts. (Hopefully it has dowels for line up.) Then find or make some steel guides (drill guides) that fit the bolt hole in the head . These will make sure you are drilling in the center of the broken bolt.  Please use a drilling/cutting lubricant when drilling.

If possible when putting it back together install studs in place of the bolts. This should make future repairs simpler.

Wishing for the best outcome on this. 

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OnaWingandaPrayer

More on the guides I mentioned.  From "Grainger".  This is something like I had in mind. You might have to make your own to size by having a boltmachined to fit the head and drilled in a lathe for centering.

Drill bushings (also known as jig bushings) install in a drilling jig to guide, position, and support drill bits, reamers, countersinks, and counterbores to ensure accurate and repeatable hole placement in metalworking tasks. Drill bushings keep the cutting tool from wandering or bending as it enters the workpiece, maximize chip clearance, and minimize the risk of marring the workpiece or the jig. Press-fit bushings are permanently pressed into a jig. Slip-fixed renewable bushings can be changed between tasks and are ideal for applications where bushings are expected to wear out before the job is done. Headless bushings can be installed close together. Headed bushings have an overhang, or head, that prevents them from being pushed through the jig and are well suited for applications where loads or vibration could cause the bushing to move. Liner drill bushings are installed in a jig to hold renewable bushings in place and ease replacement of worn or damaged bushings.

 

Fractional-Inch Standard-Wall Slip-Fixed/Renewable Drill Bushings

10Z301_AS01?$lgthumb$
These slip-fixed/renewable (SF) drill bushings come in standard sizes expressed in fractional inches. Standard-wall slip-fixed drill bushings have thicker walls and are typically sturdier than thin-wall slip-fixed drill bushings.
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scraper

Comply still it's harder than the grade bolt your using just don't try to speed through it and use oil.

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scraper

Dam spell check. Cobalt drill bit.

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OnaWingandaPrayer

Any progress on this problem bolt ?

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dwsonar

No, this is on hold. More worried about getting the bike running again now. Bought a used set of carbs to try, and still have to find the vacuum leak. This virus crap has me almost shutdown at work, so money is tight again.

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