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Need Advice - Broken screw removal

  • Thread starter Thread starter DC_GS850
  • Start date Start date
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DC_GS850

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To make a long story short - I broke an intake boot screw off flush with the head. Had the carbs off to rebuild and thought I'd go ahead and replace the intake boots while I was at it - big mistake. 7 of the 8 screws came out without much trouble. The last screw for some reason was rusted/corroded fairly badly and sheared off flush with the cylinder head. To make matters horrible I broke off a drill in the screw trying to drill it out. At this point I have tried: rust-dissolving penetrants, heat, forward and backward torque - that sucker is stuck. I am ready to admit defeat and have the screw burned out with EDM or some other drastic measure.

Here are my questions (finally)
1. Does anyone have a magic technique that might be tried?
2. Any recommendations that might be easier/cheaper than having the screw burned out?
3. If I have to have it burned out is it better to remove the head or the entire engine?

Thanks
 
There is no easy way around this one, but there's maybe one thing remaining to attempt before EDM. If you have access to a Dremel type tool or know someone that does, chuck a tiny cutting disk into the Dremel, and try to cut basically a common screwdriver slot into the end of the broken screw. Admittedly, it's not the best method of trying to turn something, but it's better than nothing. The smaller the diameter of the cutting disk, the better. You want to cut as deep a slot in the broken screw as possible, while cutting as little as possible into the head material surrounding it. Some cutting on the head will be almost unavoidable, but keep it to a minimum. Remember as well to try and cut the slot parallel to the edge of the port, as opposed to straight at the intake port. less chance of cutting into the area that the o-ring has to seal up.

Back to the Dremel tool... the cutting disk you desire will not be a tiny steel saw blade, but will look like a tiny sandpaper disk. It will usually be a core disk of something like fiberglass or a resin of some type with an abrasive grit bonded to it's surfaces. The wheel itself will somwhat wear down even tinier as it is used, and that's ok. The abrasive disks are designed to do this type work, and they work well.

Once you get a slot that will hold a screwdriver, begin again with the penetrants, heat and whatever you have available to help break it loose. Do not try to do the whole thing at once, use moderate torque to try and turn the screw. If it doesn't move, back off and add penetrant, or heat or even tap on the back of the screwdriver while it's in the screw, then try again to turn it. Just do your best to avoid stripping out your slot. If all else fails, then the EDM is possibly your best bet.

Once you get the screw out and are ready to install new hardware, consider stainless steel allen head bolts, and use anti-seize on the threads. It will not affect the tightening torque enough to matter, and it will keep the threads from galling in the future.

ANYTIME that dissimilar metals are used against one another, there will be a tendency to corrode, and heat or moisture will aggravate that tendency. In this case, you're using a steel screw against an aluminum head. There is no way around it, the different types of metal creates an electrolytic reaction between the surfaces. Corrosion. Anti-seize won't stop the corrosion, but will create a lubricating film between the metals that allows them to turn against one another even with high torque present. Even stainless is not proof against the corrosion of this type, it's simply more on the aluminum side. There are very few places on a bike that can't benefit from anti-seize. Exhaust hardware especially.
 
I would try a carbide tip bit in the dremel and carve the $#!t out of the drill bit until you can get past it. Your not going to enjoy this very much. You might be able to use the dremel to remove some of the bolt as well. You might be able to use a bolt extractor only if you remove 80% of the bolt and can get the extractor in pretty deep.

I don't like extractors, they break off too. But if you can drill out the bolt to the limits of the the threads you might have a chance. I would drill it out completely and retap the hole. There is plenty of metal there and it does not get too hot.

Good luck. At least the sun is not shining and motorcylces are not zooming past your house.
 
Thanks to suggestions by Davedanger and duaneage. duaneage had the "magic trick" and I would recommend it to others. I bought a 1/8" rounded end single cut solid carbide bur, ran it in my dremel, and it went through the !#$ing screw like it was butter. Still have to clean up the hole, but I can see the light at the end of the tunnel. Thanks again.
 
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