Advice for Broken Thread Tap in Cylinder Head

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threeputtpar

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OK, so here's what I'm dealing with at the moment on a snowblower that I'm working on:



The muffler bolt broke off upon removal, but there wasn't enough left to grab on and remove so I ground it down flat, center punched, and drilled it out. I picked out all the small bits, but there was still some left in the threads so I started tapping it. Well, I got impatient and pushed the tap a bit too much and this is what happened.

The hole is 75% open on the back side, because one of the cooling fins partially blocks it, so my only real option is to try to get the tap out the way it went in.

I'm open to all suggestions, but keep in mind it's mounted to a 200lb snowblower so taking it anywhere but my garage is probably not an option.

Does anyone have one of these, or at least successfully used one in the past?

http://www.waltontools.com/products/extract-machsc-hand.htm

I can buy one if I know that it will work. The broken tap is a 5/16 - 18 4 flute, and it was from an old Craftsman set, so it's very good quality HSS material and not just a basic carbon steel bit.

Thanks in advance.
 
No welder available, and I don't have any welding skills.

Yes, it's pretty hard steel. A cobalt bit didn't even dent it. I have a MAPP torch, but I'm leary of damaging the aluminum before the tap gets hot enough.
 
The tap extractors work well, i have used them many times.
If its not too deep you may be able to tap it around with a small punch and small hammer with short sharp taps.
You can make it a little easier if you warm the casting (not the tap) with a propane torch just get it hot, aluminum expands a lot more than steel so it may just loosen it enough to tap it around with the punch.
 
Trav, thanks for the advice. I have a tank of propane, so I'll use that instead of the MAPP gas and warm it up a bit.

It's in there deep, so the best I can reach it with for now is a small awl stuck straight it. Maybe after heating it a bit, I can jam the awl in there and try to tap it a bit to get it to break loose. I think if I can at least get it to break free and get one rotation, it should get back into the threads it already cut and come out easy.
 
I had the same thing happen to me once on an old Gravely T-head engine.

Its hard to tell how much space you have to work with. How I got mine out was I got one of those tiny flathead screwdrivers used for eyeglasses. I put it in the spaces between the tap cutting edges and lightly tapped with a hammer until it started to move. Once it started turning, I used a drill bit with the drill on the reverse setting to back it out. Hopefully this works for you.
 
Originally Posted By: threeputtpar
Trav, thanks for the advice. I have a tank of propane, so I'll use that instead of the MAPP gas and warm it up a bit.

It's in there deep, so the best I can reach it with for now is a small awl stuck straight it. Maybe after heating it a bit, I can jam the awl in there and try to tap it a bit to get it to break loose. I think if I can at least get it to break free and get one rotation, it should get back into the threads it already cut and come out easy.


Don't forget the PB Blaster
 
Once you get it out drill the whole thing out and use a hardened bolt & nut on the backside with red loctite. Don't bother tapping it again. If the fins are in the way...drill some of them away as well. If you do get an extractor and it works...don't forget to buy a lottery ticket.
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More good suggestions, guys. I didn't think of micro screwdrivers. They should fit and be sturdy enough to hit with a hammer.

Doog, as soon as it comes out I'll check the threads and if they are damaged at all it will be drilled out bigger and an insert will be red locktited in. It's not the first time I've had to drill out on a snowblower and use an insert, so I know it will hold with red locktite.
 
I hate it when that happens.

Don't worry too much about heating the tap. The aluminum will not melt before the tap does. The aluminum is fantastic at heat transfer and therefore it won't be a problem. With the provision that you don't go absolutely crazy and use an absurd amount of heat, such as using a cutting torch.

Just an FYI, Rodman brand drill bits will drill right through a tap or a file. It's the carbide tip and technique that does the trick.
 
I think tonight I'll give a dremel a try wiht a carbide bit and see if I can get a slot cut into it for a screwdriver bit and use a cordless impact to get it to back out.

If not, a little patience with the dremel and try to cut it into little pieces and pick them out.
 
A little update and a repost of the original picture.

http://s34.photobucket.com/user/jamesm09...?sort=3&o=2

I tried the Dremel with a carbide bit and it did nothing. OK, so I caved and ordered a broken tap extractor and proceeded to break the extractor's fingers twice before giving up.

I think this has come down to having to drill several small holes around the current hole and try to remove the tap that way. Then make a good hole and red Locktite in a thread insert and hope it holds.
 
Looking at the picture, if you try drilling holes where the little wholes are, you may not have enough material left to re-tap or have any supporting strength.

I would try the extractor again with lots of lube and move the extractor back and forth, trying to loosen the bit.
If that doesn't work, use heat and again twist the extractor back and forth, trying to get the bit loose.

You can also try using a center punch and lightly tap the edges where the little wholes are, again trying in both directions. Once loose, use the extractor to remove the broken piece.

Last resort would be to use the center punch, make sure it's the one you don't want to keep as it will be most likely ruined. Put it right in the center and start smacking with the hammer in hopes of breaking the brittle tap material. Then just remove the pices. Cooling the tap down with liquid air in a can may help with this.
 
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The machine is still fully operational with just one bolt and the smaller flange screw to hold the tab onto the head. It's just in my nature when doing a project like this to get everything right if possible.

I think my next attempt may be a couple of cans of computer dusters turned upside down to freeze the tap and then try to remove it with the extractor.
 
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