Author Topic: Major screw up...miracle required (broken bolt)  (Read 881 times)

Offline UncleD

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Fitting an SRM sump to the A10 today. 

Two of the studs had been replaced with oversized bolts so I had the appropriate helicoil on hand.  The holes didn't need drilling so I just ran the tap through them a couple of times to clean them up.  The first helicoil fitted easily however the second caught on something on the way in but with a little force screwed into the appropriate depth.  When I inserted the bolt as a test run however it caught so I progressively pushed it a little and the backed off hoping to straighten out whatever was catching it...

...yep, I pushed too hard and the bolt snapped off in the engine casing.  There was copious obscenities.

Anyway, what can you do?  I got out the extractor bits and drill and started to work on removing the broken bolt end.

5 hours later (laying under the bike on the concrete floor in 38 degrees) and I have all but drilled away the offending bolt as the extractors just don't grip enough to turn the bolt.

The trouble is that I am now a little off centre and in danger of damaging the engine casing.Im not sure if I have drilled away any of the the helicoil but it is not moving and is refusing to let go of what is left of the bolt.

I am at the end of my expertise.  Any tips ?

Is this the greatest excuse ever for an engine rebuild?




Northern Territory, Australia

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Re: Major screw up...miracle required (broken bolt)
« Reply #1 on: 05.01. 2019 08:21 »
Oh BUGGA.
Which one is it, top or bottom?
Well you've learnt one lesson. Never force a helicoil/recoil. If it snags (jumps a thread/cross threads) pull it back out by unwinding it. I'd say there was some of the old bolt thread left to upset it.
Time to get the old Dremel and diamond burr to eat it out. If you can get it thin enough you might be able to pick it out with a sharp scribe.
Once all the steel is out we'll have to think of a repair. Leave that with the minds trust to chew over.
Cheers
'51 A7 plunger, '57 A7SS now A10CR, '76 XT500, '77 AG175 '83 CB1100F, '81 CB900F project.
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Offline Swarfcut

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Re: Major screw up...miracle required (broken bolt)
« Reply #2 on: 05.01. 2019 08:42 »
 UncleD.... If you have any of the bolt left, try a parallel sided splined bit, typically a long nosed TORX bit hammered into the off centre hole in the bolt.  Stands a good chance of gripping, just slightly oversize will do. Conventional  stud extractors have a taper which spreads the stud and are rarely successful with small diameter holes.

  As Musky says the helicoil will have to be persuaded out with a sharp scribe. With a bit of luck this may leave a thread still capable of supporting a new helicoil. If not, depending on the size of the hole  you end up with, the answer is a custom insert to allow a standard bolt or stud, or a shouldered  retaining stud, 1/4" stud then bigger diameter to suit the size of the hole butchered in the crankcase. This will need a coarse thread, where it fits into the crankcase, typically Whitworth or M8 or M10 if you are extremely unlucky.
 
 Shit happens....     But this is merely a ripple on the millpond of life in the grand scheme of things.

  Swarfy.


  Additional.....    on reflection Slymo's following solution of the insert plug will be easier. The oil sump plate can be used as a drill guide to locate the mounting stud.  Stick with studs ....saves wear on the crankcase threads and avoids possible blind hole bottoming and crankcase damage.

  Thanks Slymo.

Offline Slymo

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Re: Major screw up...miracle required (broken bolt)
« Reply #3 on: 05.01. 2019 08:44 »
That is a nasty problem! I would suggest the best and most permanent solution would be to remove all the offending material including the helicoil (possibly with further drilling and then a good easyout?) and then drill tap and plug wound with an oversize plug of aluminium or brass in order that you can re drill and tap to 1/4" cycle or bsf. Definitely go back to studs as bolts are likely to see tye same problem again in the future.
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Offline Steverat

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Re: Major screw up...miracle required (broken bolt)
« Reply #4 on: 05.01. 2019 09:08 »
This sounds easier than it is, but have you considered building up the casing with an aluminium braze like "Lumiweld". It is not a weld so there's no melting of the parent metal, and so no deformation, but its very strong and can be drilled and tapped, and looks like aluminium. The problem would be access of course and the need to get the substrate really clean for the braze to adhere, but I think you could do it in situ. Do you know someone with a pit in his garage? If you can park the bike across it that will save the backache a bit.

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Re: Major screw up...miracle required (broken bolt)
« Reply #5 on: 05.01. 2019 10:01 »
G'day fellas.
Once all the steel is out the sump plate can be used as a guide (make a steel dowel to fit in the sump hole the size of the tapping drill 5mm) to drill the hole deeper and tap that.
Cheers
'51 A7 plunger, '57 A7SS now A10CR, '76 XT500, '77 AG175 '83 CB1100F, '81 CB900F project.
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Offline UncleD

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Re: Major screw up...miracle required (broken bolt)
« Reply #6 on: 05.01. 2019 10:11 »
It is the hole on the timing side, closest the front wheel.

Dremmel...ok, there's a thought.

Oversize torx bit...can't make things worse.

Luminweld...new territory but she understand the principle.

Thanks for the ideas to move forward (and no mention of a rebuild)!

Northern Territory, Australia

Offline Swarfcut

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Re: Major screw up...miracle required (broken bolt)
« Reply #7 on: 05.01. 2019 10:17 »
G' Day Musky, Happy New Year.

     Always difficult to appreciate the other guys situation but on the face of it drilling and tapping the hole deeper as you suggest is by far the simplest answer, assuming there is  enough material below the existing hole.

  Lying on concrete at 38 degrees sounds  like luxury to me.

  Swarfy.

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Re: Major screw up...miracle required (broken bolt)
« Reply #8 on: 05.01. 2019 10:20 »
This is related but a bit late for uncleD but I'd welcome any comments, I bought a set of left handed drills some time ago,  never used them as yet, anybody had any success with them in removing broken studs
All the best - Bill
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Re: Major screw up...miracle required (broken bolt)
« Reply #9 on: 05.01. 2019 10:33 »
Depending on how much damage there is to the hole a timesert or big-sert https://timesert.com.au/  or  http://www.crosstools.com.au/oversize-big-sert-thread-repair-for-badly-damaged-hole.html
You'll still need to make a jig to ensure the hole is in the right spot and square.

G'day Swarfy, HNY. I try to make things simple but am guilty of over thinking at times.

G'day Bill, yes they work if the broken bolt isn't bottomed tight.

Cheers
'51 A7 plunger, '57 A7SS now A10CR, '76 XT500, '77 AG175 '83 CB1100F, '81 CB900F project.
Australia
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Offline RichardL

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Re: Major screw up...miracle required (broken bolt)
« Reply #10 on: 05.01. 2019 14:13 »
Musky, and all

I have done helicoils for the sump plate while on the center stand, but this here is a more complicated job. If no pit, maybe the bike can be laid over on an old mattress or something. Bikes do, occasionaly, end up on their sides.

BigSert or other oversized insert seems much better and easier than plugging and drilling out the plug. I seem to recall seeing an insert-in-insert product once, but can't recall the name. I do recall that it seemed hsrd to come by, even in 6mm.

Two other things mentioned here I would avoid. First, trying to drill out rather than wind out the old helicoil. May not work, then leaves not enough to unwind. Second, Lumiweld.  I've been trying it. Watched the videos and it's not as straightforward and easy as it looks (at least, for me). I was working on what would have been a scrap timing cover and it did melt through, twice.

EDIT: Not saying Luniweld is no good, but making the bottom of your crankcase an early experiment seems ill advised. My A7 crankcase is at the machinist right now and one of his jobs is to rebuild (by welding) one of the sump screw bosses. Not a job I trust to myself.

Gotta go.

Richard L.


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Re: Major screw up...miracle required (broken bolt)
« Reply #11 on: 05.01. 2019 16:41 »
My youngster had a bodgy helicoil in his Hoonda head, so tried to clear it with a tap-which also snapped off- inside (no protrusion)...a bit harder than a stud, but we got it out with a previously mentioned diamond Dremel tip (having the three flutes in the tap helped)...in hindsight, some cutting oil may have helped..
 
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Re: Major screw up...miracle required (broken bolt)
« Reply #12 on: 05.01. 2019 16:55 »

I had to do this exact same job on mine due to 2 broken studs (discovered when fitting the SRM bit, and explained the weepiness), and it has been OK for years.

I made a guide jig from half inch plate with the 4 quarter inch holes very carefully marked out and drilled in the right places (I clamped the stock for the jig to the original sump plate), attached it to the crankcase by the 'good' corners, and used the 'empty' holes as guides to get the busted bits out. Drilled out to just under  85% tapping drill size for the original thread, picked out a few remnants with a scribe, drilled to final tapping size, ran plug tap down them - and was lucky enough to get away with it. But I didn't have a buggered helicoil to contend with - just the old studs.

I found it very worthwhile to make the first drill bit into a home-made end mill or slot drill by grinding the tip off to get a flatter-ended cutter that didn't tend to wander and/or fret against the guide, and it was also helpful to have shortened it as much as possible to get 'rigid'.

In this case I'd follow the same routine, drilling undersize to start with and increasing to the size needed for the helicoil tap. Which would mean taking the jig off to enlarge the guide hole, maybe more than once, and doing the sequence several times. You should end up with a clean threaded hole that will still accept the intended helicoil if there's a god; but as he's not always at home when we need him, you might have to go bigger, and settle either for a stepped stud if you can sort one out.

My SRM gizmo came with caphead screws which I saved or some other job, because if ever there's a place where studs and nuts (nylock or double nuts even with lockwashers), is a must-have, this is it. Maybe SRM have moved on by now, as I'm sure a good few people will have mentioned they didn't like screws where studs are obviously far better.
Bill

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Re: Major screw up...miracle required (broken bolt)
« Reply #13 on: 05.01. 2019 17:43 »

 groily, without going too far off-thread (so to say)- did you do that with the engine in place ?  *respect*  *beer*....I'm reminded that I have a simple stripped thread, and made a kind of 'jig', but upside down is very tricky...decided it can wait as there's enough thread to hold a longer socket cap screw  *bash*... for now
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
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Offline kiwipom

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Re: Major screw up...miracle required (broken bolt)
« Reply #14 on: 05.01. 2019 19:28 »
This is related but a bit late for uncleD but I'd welcome any comments, I bought a set of left handed drills some time ago,  never used them as yet, anybody had any success with them in removing broken studs
hi guys, a challenge indeed here but `Left hand Drill Bits sounds like a good idea to me, i have in the past used one of these where after a small amount of drilling it grabbed the offending stud and wound it out, cheers
  p.s. must get some for myself. 
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