Broken bolts

Re5Guy

Re5Guy

Junior member
Location
New Zealand
Hi all,

I'm pulling apart the Dellortos on my Corsa and despite my best efforts four of the nine M4 bolts that hold the diaphragms to the carb bodies have sheared off at the head. I swear they are made of swiss cheese!
Anyhow their softness makes me think that this must have been a problem for others so I am looking for words of wisdom.
I have tried soaking them in penetrating oil for several days. I also figured out that there is a hollow recess behind the bolts in the carb so I drilled a 1mm hole into each and filled them with penetrating oil. I have also gas heated and then "frozen" the bolts (CRC Freeze Off).
No joy at all, all I am doing is slowly shortening what is left of the bolts as I apply "persuasion" with a set of vice grips.
The photos are of the worst carb, one carb came apart easily and the other just one bolt snapped. On this later one I locked on two nuts down at the base of the thread as the thread was still good, this was to give me better leverage, all that did was strip the thread on the bolt!
Obviously I am trying to get them out without having to resort to the drill and risk damaging the carb body.

Any ideas anyone?
broke1.jpgbroke2.jpg
 
Vice grip or saw a slot in the end of the screw and use an impact driver.
To further enhance your discouragement, there's absolutely no need to dismantle those pumps anyway.
Paul
 
Best investment I ever made was a mini electric impact driver from MAKITA.
Worked really well during dismantling of my old FZR carbs that had been sitting for more than 20+ years.
Doesn't help in your situation I know, a consideration for next time round though?
 

Attachments

  • FB_IMG_1714996178981.jpg
    FB_IMG_1714996178981.jpg
    103.5 KB · Views: 26
If you're in the UK, try repeatedly heating and then Loctite Freeze and release, not too much heat as the aluminium can melt if it's a map torch...if that fails send it to Ged Shorten at GCS Laverda or any trusted engineering machine shop and they'll be able to set it up on a machine tool and get them drilled or machined out.
 
looks to me like they may have been loctited in, totally not required, but since you have a good bit of bolt protruding you are onto a good start, I would heat the protrusion with an oxy acet flame until it is positively glowing red hot, this will require a bit of skill in order to not melt the alloy, so going in an out with the torch on maybe a no2 nozzle will get them hot, next weld a flat bat with a hole drilled into it onto a bolt and making sure that its still red hot, (the bolt not the weld) lever it loose, if it moves 180 degrees, it will move more when cold, and the you can lubricate it to good effect which doesnt work when its cold except to shrink the hot bolt, the alloy will always expand more than the bolt.
CLEM
 
Shuggie said:
If you're in the UK, try repeatedly heating and then Loctite Freeze and release, not too much heat as the aluminium can melt if it's a map torch...if that fails send it to Ged Shorten at GCS Laverda or any trusted engineering machine shop and they'll be able to set it up on a machine tool and get them drilled or machined out.
Click to expand...
New Zealand hasn't been in the UK for a long time and sometimes foreigners can be quite good. Apparently they even build motorcycles and carbs nowadays.
:)
Paul
 
Weld a nut on the protruding thread and then try to undo it with a spanner while still hot. Any fixings sheared flush that won't drill out, although most of them should; there is then always the option of spark erosion. This has the advantage of being extremely accurate and wont damage surrounding material. I have had this process done on hard to access sheared bolts, it works very well. It will cost money of course, but a quick search on the worlds favourite search engine does bring up these companies in New Zealand.
 
6mm DT 175 exhaust stud, I do a fair bit of these snapped bolts for local bike shops, as I say to most people, dont try this at home kids, drilling and market stall "easy outs" are anything but, and they make the job harder when they snap off as they invariably will, then I have to use the TIG torch to anneal the easy out
 

Attachments

Thanks for all the replies Gents....my responses in no particular order...

In my case I've found that I do need to dismantle these. The diaphragms are original and one was cracked.

I've got a small impact driver, but using it occurred to me too late.

They aren't Loctited, they just have never been undone and the bike has been sitting for years.

Given the amount of heating and freezing and soaking I have been giving them, I think a trip to a machine shop is the safest bet.

GregT I am in the Wairarapa, you know anyone down this way you would recommend?

cheers,
Tony
 
Pauls said:
Weld a nut on the protruding thread and then try to undo it with a spanner while still hot. Any fixings sheared flush that won't drill out, although most of them should; there is then always the option of spark erosion. This has the advantage of being extremely accurate and wont damage surrounding material. I have had this process done on hard to access sheared bolts, it works very well. It will cost money of course, but a quick search on the worlds favourite search engine does bring up these companies in New Zealand.
Click to expand...
We used this method in aviation all the time. Typically after buggering up the broken bolt trying to drill and Eze-out.
 
"a small carbide end mill!"
I think you mean a slot drill, end mills are for milling on an end or an "edge"

in my Timcert kit there are 3 slot drills for use with 6mm, 7mm and 8mm, I bet the next time I need one it will be 9mm, 10mm or 12mm, I shudder to think what the cost of that metal case containing all those drills, countersinkers, taps and and inserters would be npw, wrong side of £500/£600 probably
CLEM
 
You must log in or register to reply here.
Back
Top