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Sheared bolt extraction?

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Sheared bolt extraction?

Unread postAuthor: Ragnarok » Fri Sep 11, 2009 3:12 pm

I probably should have posted this up a few days ago, but it's only really just occurred to me to do so.

Anyway, a rather elderly bolt holding the engine of our narrowboat to one of its main mountings has sheared off, leaving half the bolt thread in the tapped hole.
Because of the importance of the bolt in question, it's not a case of just leaving it - the remnants have to be removed, and it has to be replaced.
All of it has to come out, and with minimal damage to the surrounding engine.

I've got a set of bolt extractors handy, but I have very little experience with them. I wondered if anyone had any better suggestions or simply advice for dealing with the situation (both personal experience and sensible speculation are welcomed).
It's not really feasible to move the boat anywhere where the engine can be removed, because to do so, the engine would (obviously) need to be run, and so it has to be done in situ.

~~~~~

Image

A picture of the now-sheared bolt, and the damage done around the hole (which is about 3mm deep). The mounting bracket has been removed here.
This picture is upside down, because the only meaningful way to get access to the area is by going head first (and down) into a relatively small space.

Best we know, this is a 3/8" UNF bolt, which makes little sense for what is essentially a marinised British Leyland engine - but that's what it seems to be, based on the dimensions and thread pitch and profile of the corresponding bolt from the other side of the engine.

~~~~~

Image

The bolt in question (prior to shearing) can be seen below the 00 in 1800 in this next picture. The limited space for the bolt head (within the mounting) means that it does not look feasible to re-tap the hole and use a larger bolt (although a Heli-coil has been considered, and not completely ruled out - but it is less than ideal).

Bear in mind, the object to the right of the 1800D marking is the main fuel pump and feed from the diesel tank. It can't feasibly be moved, nor is any situation where it is at risk of damage acceptable.

~~~~~

Image

And to illustrate the limited space which I'll have to be upside down in to work. There's next to no space for anything but modestly sized power tools.
The foot in question is on the right in this image (next to the air intake filter)

~~~~~

The current plan, unless I am advised otherwise, is to drill into the bolt with first a 3mm pilot hole using a Dremel.
This will then be increased to a 4mm hole with a larger drill. It may then be increased to 4.5mm if everything remains favourable.

The bolt extractor will be inserted then, with luck, use of a tap wrench will extract the bolt. As it's not under load, the hope is that it will be relatively free moving. However, knowing this engine, it will likely be at least partly jammed in place.

If it is jammed, the plan is to then feed penetrating oil through the hole in the bolt (as I know there to be at least 5mm of space behind the back of the bolt) to settle there for a while, and hopefully free up the bolt.

If it comes out, then the plan is to then assess the thread. If it's damaged, then I'll be re-tapping the thread with a 3/8" UNF tap. If it appears good, or after the thread is improved, the mounting bracket will be replaced, and the various nuts put back into place.

~~~~~

Anyway, if you can see flaws in that plan, or have suggestions or advice, I'd like to hear about it.

If you have a better idea that may prove within the bounds of possibility, that'll do too.

If you do have any suggestions, please make sure they're not vague, because I'll only have time to briefly check this topic before heading down there tomorrow to attempt to extract, and I won't be able to hang around asking "What do you mean?"
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Unread postAuthor: grock » Fri Sep 11, 2009 3:19 pm

your plan sounds good, but if the bolt is loose, you could try using a magnet, sometimes that works to rotate the bolt out
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Unread postAuthor: Technician1002 » Fri Sep 11, 2009 3:25 pm

The plan is good. Sometimes in those situations the penetrating oil may have trouble reaching the end of the treads due to the build up of corrosion (this is marine). You don't want to drill all the way through the bolt for the extractor, but you do to get penetrating oil through. A smaller pilot type hole can be drilled on through the bolt for the application of penetration oil. One just large enough for the extender tube of the aerosol can is fine for this.

Use the drill extraction bit guide for size. Too large of a size will allow the bolt to expand and bind it tighter in the hole. Too small runs the risk of a broken extractor. Check the head of the bolt for hardness markings. High strength bolts are more brittle and harder for the extractor to get a bite onto than a soft iron bolt.

The head marking can be identified on the chart on this page.
http://www.offroaders.com/tech/Bolt-Identification.htm

I know you guys are probably well versed in this. I posted it for the rest of Spudfiles. No insult of your knowledge intended.
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Unread postAuthor: Ragnarok » Fri Sep 11, 2009 4:31 pm

grock wrote:Your plan sounds good, but if the bolt is loose, you could try using a magnet, sometimes that works to rotate the bolt out

It seems highly unlikely that the bolt will be loose enough for that to be viable, particularly given that the bolt is within a 400 pound cast iron engine.

Nonetheless, I will put one of my NdFeB magnets amongst the equipment I'm taking down tomorrow. I don't hold out vast hope for it working though.

Technician1002 wrote:Sometimes in those situations the penetrating oil may have trouble reaching the end of the treads due to the build up of corrosion (this is marine).

The engine is entirely inboard and electrically grounded. The boat has - to the best of my knowledge - only ever been within fresh water (for an interesting definition of fresh water, given what the canals look like) and has always been fitted with cathodic protection.

So, corrosion specifically because of the "marine conditions" should be limited. It should still be remembered that this engine, a BMC B-series 1800D (with a terrifying factory power output of a little over 30 horsepower*), hasn't been manufactured since 1980, and it's been fitted to the boat for at least... 13 years, I believe. The minimum of 16 years before that, I don't know about, but the likelihood is a Leyland Sherpa van.

And that reminds me that I should have mentioned earlier that the engine is almost entirely cast iron.

*Which it will no longer be getting. It's been somewhat down-regulated for marine use, and now seldom revs past about 2000 rpm of its original rev limit of 5500 rpm. It still remains enough for what it needs to do.

Use the drill extraction bit guide for size. Too large of a size will allow the bolt to expand and bind it tighter in the hole.

I've already looked that up, and the extractor for this size of bolt is marked as requiring a 4 to 4.5mm hole - so that's the size I'll be using.

Check the head of the bolt for hardness markings.

I can make little sense of the bolt's head markings:
Image

Based on our test attempts to drill this part of the bolt and fit extractors to it, I've assumed the bolt to be relatively low grade - unless of course, you can tell me otherwise.

I know you guys are probably well versed in this. I posted it for the rest of Spudfiles. No insult of your knowledge intended.

Not at all. This is something that I don't have much experience with. I know the theory of the techniques, but I've never actually put them into practise.

In some ways, I'm glad of you saying these things even if I already knew them. For one thing, it confirms I'm going in the right direction, and for another, this topic is half a demonstration (in my mind at least) of the "textbook" way to ask for help on an issue like this - a detailed explanation backed up by in focus photos.

I'm sure most veterans here would welcome more topics which actually gave them the information they needed to answer the question accurately.
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Unread postAuthor: spudtyrrant » Fri Sep 11, 2009 4:54 pm

I would drill a hole about 4mm across, and solder in a 4mm steel rod and twist it out of there.

The solder should hold up since there isn't a lot of force at work.
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Unread postAuthor: THUNDERLORD » Fri Sep 11, 2009 4:55 pm

...put them into practise...


Aha! I caught you Ragnarok!!!
(I copied it quickly too in case of possible "edit") :P

OK, well, I was thinking you could file/grind the sides flat (since it looks to be protruding(?))
Now, here's the thing Ragnarok, since you'll be hanging upside down,
The ideal tool will be a "Monkey wrench"... :P :lol:

Seriously, maybe you could cut a slot in the top with a rotary tool, then use an "impact driver" tool.
It's a thick cylindrical tube with different bits like some screwdrivers,
The end is struck with a hammer (or monkey wrench :roll: )
and the tip turns slightly during the impact.

I saw an expensive two part catalist loosener called "PB" something in an auto store other day...

Seems like the drilling and tapping will be torqueing it tighter(?)
Should work.
Heat of a torch before loosening would be very helpfull especially with the cast iron block and steel bolt (the hole expands more than bolt due to surface area difference (?), But it does.
Not really ideal with the fuel in proximity though.
Good luck! 8)
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Unread postAuthor: jrrdw » Fri Sep 11, 2009 5:19 pm

As a life long machanic I can tell you screw extracktors flat out suck!

1st thing I do in this sitsuation is use a small tipped straight screw driver and try to catch a edge on the broken area and spin it out by hand, might need a few taps with a hammer on the screw drive handle to get it turning.

2nd attempt is to grab the bolt from behind (if you can) and turn it the rest of the way through instead of backing it out.

3rd attempt would be to heat the area around the broken bolt then try the 1st idea again. This is in cast metal and will heat up and expand quickly, work fast.

Last resort is using the screw extractors. Good luck.
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Unread postAuthor: jeepkahn » Fri Sep 11, 2009 5:41 pm

See if you can find a reverse twist drill bit, commonly packaged with extractors, many times the bit will get a bite and spin it right out...
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Unread postAuthor: Ragnarok » Fri Sep 11, 2009 5:46 pm

Cock! Browser crash. Sorry, this post is cut down from the original version.

THUNDERLORD wrote:
...put them into practise...
Aha! I caught you Ragnarok!!!

I'm not seeing the problem. Assuming it's a spelling point, that is the correct version of practise.

OK, well, I was thinking you could file/grind the sides flat (since it looks to be protruding(?))

Afraid not. It's sunk in about 2-3mm.

Seems like the drilling and tapping will be torquing it tighter.

The drilling shouldn't be too much of an issue. The Dremel's emphasis on speed over torque should prevent drilling the pilot hole being too bad, although the slower 4mm drilling might be a problem.

The tapping shouldn't happen until the bolt is removed, so that's not an issue.

Not really ideal with the fuel in proximity though.

Igniting the fuel is not what I'm too worried about - diesel is hard to light. However, damaging the hose or seals in the pump is less ideal.

Anyway, even if it were feasible (and with the huge heat sink of the engine, I find it unlikely), I don't fancy using a blowtorch upside down in the limited space available. (So for that reason spudtyrrant, although I appreciate all suggestions, soldering is not really feasible.)

That said, I'll be taking one anyway on the off-chance I can find the space to use it.

@jrddw: I've never been much impressed by what I've heard of them, but it looks like one of the few options available.

There are no edges which can really be caught with a screwdriver, and as the other side of the bolt is... well, the crank casing.... that's not really possible too.
As I say just above, heating is also a somewhat unlikely possibility as well.

That said, thanks, I appreciate the help anyway.

@jeepkahn: I had thought about that. I don't currently have one handy (although I may swing by a DIY store early tomorrow...), so I'll probably try without first - particularly as I expect that it'll be too stiff for it to be that easy, given the likelihood of thread damage.

That said, if it suddenly shifts when I try drilling, I'll have little choice but to get my hands on one.
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Unread postAuthor: jrrdw » Fri Sep 11, 2009 6:44 pm

If you sharpen a screw driver tip good and sharp you can get it to bite into the broken surface face. Like you said there is no load on this it should turn out pretty easy, as long as the threads in the hole the remaining bolt has to ride in are in good shape.
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Unread postAuthor: THUNDERLORD » Fri Sep 11, 2009 6:56 pm

Ragnarok wrote:I'm not seeing the problem. Assuming it's a spelling point, that is the correct version of practise. ...


Cool, I try to learn something new everyday.
I guess if you want to learn English better, ask an Englishman:
Practice is the noun, and practise the verb (though not in the USA, when it is practice): I'm afraid I'm rather out of practice; Why don't you practise what you preach? See also practical. To spell the two words correctly, remember advice (noun) and advise (verb).


In USA it seems to always be "practice". :? :oops:

Since your bolt is broken a few mil.s inside the thread,
Seems like a penetrating lubricant type liquid could sit there overnight maybe, beneficial for whatever method for extraction...
Still recommend heat (and what Jrrdw mentioned).
It'd be cool to see a pic of the whole boat BTW.(?) 8)
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Unread postAuthor: inonickname » Fri Sep 11, 2009 7:02 pm

You could put a smallish metal rod down there dipped in a loctite retaining compound or something, then come back and unscrew it in half an hour.

I don't know if they're similar to bolt removers but you could use a broken tap remover.

If all else fails you could drill out the thread and repair with a thread repair kit or re-tap the hole and replace with a larger bolt.
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Unread postAuthor: dewey-1 » Fri Sep 11, 2009 7:36 pm

I agree with jeepkahn on the use of a "reverse" twist drill.

Many times just using that type of twist drill loosens the bolt, just from the vibration and direction of drilling.

That is usually the best first attempt and then the screw extractor.

It always seems like the extractor snaps before before the bolt loosens.
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Unread postAuthor: Ragnarok » Fri Sep 11, 2009 10:07 pm

jrrdw wrote:...as long as the threads in the hole the remaining bolt has to ride in are in good shape.

This is the downside. Because of the way the bolt has sheared off, I can only expect the threads are buggered.

THUNDERLORD wrote:Since your bolt is broken a few mils inside the thread, seems like a penetrating lubricant type liquid could sit there overnight maybe.

Given the axis of the bolt is horizontal, it'd need something fitted over the outside to hold the oil in place. Still, it's a possibility.

It'd be cool to see a pic of the whole boat BTW.(?)

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It's supposed to be a somewhat relaxing pastime - I more think, bizarre. On the last trip out alone, we ended up with a duckling in a bucket, in an attempt - eventually successful - to return it to its mother, each of which were on different sides of a lock.
You've not played the old fairground game "hook a duck" until you've done it with a real duck. (My imaginary lawyers require me to inform you the duck was not harmed in the process.)

@inonickname: I alluded to thread repair kits earlier - Helicoils is one of the names they're sold under. Still, it's not going to be as strong or secure, which is why I'm trying to avoid it.

Larger bolts aren't really an option either, given the truly marginal space available for the bolt head within the mounting. Much larger, and you could no longer apply a socket to it to remove it (and there's not the space to swing a wrench).

@dewey-1: If I can get hold of a reverse twist drill, I'll use one. Whether I can get hold of one is another matter.

I know of the trouble that comes with extractors (namely, them breaking off, and making things worse). However, if it's so jammed that an extractor's not up to the job, then reverse drills clearly won't manage it either.
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Unread postAuthor: D_Hall » Fri Sep 11, 2009 10:27 pm

You never said (or perhaps I missed it): How did it get torqued off? Over torquing? Trying to loosen a corroded bolt? Etc.? That can make a difference regarding what may or may not work.

Best thing I've ever used is liquid nitrogen. Works *beautifully*. But in the space/configuration you've got I doubt it would work.
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