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Snapped Fastening Bolt

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tflick
Deckhand

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Canada
10 Posts

Initially Posted - 05/11/2009 : 13:27:23

I started the process of doing maintenance on my swing keel. After removing three of the four fastening bolts, I ran into a stubborn fourth. I became impatient and put too much force behind it and snapped the head off the bolt with approx 3/4 of it left behind. Does anyone have any idea how to remove the stem of the bolt? I am guessing this is not good.

Edited by - on

Prospector
Master Marine Consultant

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Canada
3159 Posts

Response Posted - 05/11/2009 : 13:47:51

Hi Todd and welcome to the forum.

I don't have much experience with the bolts you are referring to, but I have broken many bolts on engines. 3 Solutions come to mind.

1. Let the bolt soak overnight in a solution like deep lube which breaks the bond between the metals of the bolt and whatever it is bedded in. Heat the bolt cherry hot. Put vice grips on and pray. Similarly, you can sometimes weld a nut onto th estub to act as a new head, and get the bolt out, but I wouldn't do welding in my bolt, so I guess you wouldn't do that in yours either.

2. Drill out the centre of the bolt using a drill with a diameter just a little smaller than the bolt diameter. One its been drilled out, the remaining threads will lose their strength, and can be backed out using an easy-out from a store like Canadian Tire. An easy-out is basically a tapered drill bit with a left hand thread. The more you tighten it in, the more it pulls the screw out.

3. Grind the bolt flush to the surrounding metal, then drill oversized and using a hand tap, tap the hole to accept the next larger size of bolt.

Here's more info... http://www.toolvice.com/screw-extractors.html

Edited by - on

Dave5041
Former Mainsheet Editor

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USA
3758 Posts

Response Posted - 05/11/2009 : 13:53:02

Definately not good. Drilling a stainless bolt to use an ez-out is a slow and tedious process, but probably the only option. I first ground a dimple in the center with a dremel on a bolt I broke. By carefully locating that dimple, it is easy to keep your first bit centered. Start with 1/16", you will need several, and be patient. Flush the hole frequently with cutting oil since you can't keep it wet drilling up and be careful of pressure - you don't want to break a titanium oxide bit and lodge it in the hole. Go up one drill size at a time (3/32, 1/8, 5/32, 3/16, and maybe 7/32) until you have the largest hole that you can safely drill without damaging the threads and use the largest ez-out that will fit. I wouldn't try the broken screw removers that bite into the end of the bolt because stainless is to hard. After you get it out (think positive), lubricat a thread chaser or another bolt and screw it in and out several times to clean the threads. If you don't succeed, having the fitting replaced is the next option, and I suspect that will be expensive.

Edited by - on

Prospector
Master Marine Consultant

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Canada
3159 Posts

Response Posted - 05/11/2009 : 14:02:30

Dave - Stainless work-hardens very quickly. I'm not sure that the re-drilling is a good idea. has this worked for you in the past?

Drilling with a left hand drill bit and teh tool running in reverse may work as well. http://www.irwin.com/irwin/consumer/jhtml/detail.jhtml?prodId=IrwinProd100125

Edited by - Prospector on 05/11/2009 14:04:21

Dave5041
Former Mainsheet Editor

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USA
3758 Posts

Response Posted - 05/11/2009 : 20:20:07

I have drilled stainless on a previous boat, and my experience has been that repeated drilling with small increments in diameter has been successful. I tried going from a small pilot hole to a 3/16" bit on one occasion and did nothing but generate a lot of heat and dulled a bit. Small increments will generate less heat and frequent flushes with cutting oil provides additional cooling. It's not a fun time. I said titanium oxide before, but I ment titanium nitride unless you want to protect the piece from sunburn.

Also, I don't think the fitting's wall thickness is adequate for over drilling and re-tapping. Additionally, I don't think there is adequate depth in the fitting for the tapered portion of the tap and tapping 3/4" of stainless would be even less fun than drilling. For me, replacing the fitting would be a job for a pro.

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Dave5041
Former Mainsheet Editor

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USA
3758 Posts

Response Posted - 05/11/2009 : 20:26:23

Left hand bits, if you can the size assortment for a reasonable price, might be worth trying in case it breaks the bolt loose. There are only 4 bolts holding the keel on, so there is no room for shortcuts.

Edited by - on

Dave5041
Former Mainsheet Editor

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USA
3758 Posts

Response Posted - 05/11/2009 : 20:33:00

One other thought, if the casting can be removed since the other bolt is out you may have 1/4" of bolt shaft sticking out to try other options.

Edited by - on

Happy D
Admiral

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921 Posts

Response Posted - 05/12/2009 : 14:40:43

If you have enough sticking out, I usually put a nut on the broken piece and weld it on. The heat helps the threads let go and you can get a socket on the nut and back it out.
Even if you can't weld to it, heat the broken piece up red hot and let it cool to ambient a few times. That might loosen up the threads.

Edited by - on

psechrist
1st Mate

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USA
29 Posts

Response Posted - 05/12/2009 : 14:58:35

If you do any drilling of stainless be sure to use low speed. Stainless does not like high speed when drilling. It will burn up a drill bit at high speed in a heart beat.
Heating cheery red & then letting it cool down will expand the bolt in the hole & usually will release with vise-grips.
Oh the joy of stuck bolts,
Pat Sechrist.

Edited by - on

Dave5041
Former Mainsheet Editor

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USA
3758 Posts

Response Posted - 05/12/2009 : 19:34:16

Pretty gutsy torching an overhead bold surrounded by fiberglass. A couple o quick zaps if you can get a nut on it might not damage the fiberglass. The fitting is a threaded stainless tube with a tang that is imbedded in fiber glass. Polyester doesn't like glowing metal.

Edited by - on

tflick
Deckhand

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Canada
10 Posts

Response Posted - 05/16/2009 : 14:08:01

Thanks for all your suggestions. I dropped the keel and discovered the bolt had broken flush with the weldment. I tapped the end of the bolt and started drilling out the centre until I got up to 1/4" drill bit. It was a long process, drilling slowly as suggested and frequently dipping the drill bits into oil to reduce friction. Up until this point, it looked promising. The drilling was slow but the bolt was quite soft to drill.

I then used an easy-out to try and remove what was left over but no luck. The thing would not budge. I didn't want to apply much force on the easy-out for fear of snapping it off.

I then tried heat, shooting a blow torch up into the hole of the weldment. But I stopped when the fibreglass around the hole opening started to bubble and turn black. I then retried the easy out but it did not budge. Any further suggestions?

Edited by - on

mlg3733
Navigator

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118 Posts

Response Posted - 05/16/2009 : 15:12:01

I have had success with drilling almost up to the bolt width and then using a tap. It was not in stainless steel, though.

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Ed Cassidy
Captain

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USA
365 Posts

Response Posted - 05/16/2009 : 17:46:46

This from a former mechanic, continue drilling with the next larger bits, working your way to 11/32. The bolt is 3/8 and the od of the piece it is screwed into is 5/8. Hopefully, along the way to 11/32, if you drilled dead center into the bolt, the threads or what is left of them will come out. Forget putting any force on the easy out. If at 11/32, nothing gives, drill with a 'U' (23/64) drill bit and tap for a 7/16 bolt. Be sure to use a bottoming tap to finish the hole after first tapping the hole.

Edited by - on

Dave5041
Former Mainsheet Editor

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USA
3758 Posts

Response Posted - 05/19/2009 : 09:32:38

ED's approach sounds good. I just want to add that if it was easy to drill, your problem probably started with an inappropriate bolt.

Edited by - on

Dave5041
Former Mainsheet Editor

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USA
3758 Posts

Response Posted - 05/19/2009 : 09:45:35

If you do overdrill and tap, you might consider a Helicoil insert to stay with the same size bolt rather than 3 and 1 and drilling out the casting.

Edited by - on

Ed Cassidy
Captain

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USA
365 Posts

Response Posted - 05/19/2009 : 11:13:34

Dave,
Two excellent points and Helicoil is available in stainless.

Edited by - on

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Notice: The advice given on this site is based upon individual or quoted experience, yours may differ.
The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.