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Rear Radius Arm Bolt - The 'normal' Nightmare.....


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#1 Avl_Paul

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Posted 22 March 2020 - 03:55 PM

So, I realize this has been covered before and I've read a few threads of recommendations - most of them don't make any sense to me and it sounds like they are dealing with subframe bolts as opposed to the radius arm bolts...here's my experience so far and I am hoping for some advice:

 

I watched 2 different videos on how to remove the rear radius arms.  Both started with older Minis than mine and more corrosion form the UK (mine is '95 that has been garaged most of the last 20 yrs) and neither had much issue with the bolt heads breaking off so I approached this job cautiously but not as cautiously as I should have!  I soaked with PB-Blaster and Aerokroil for a couple of hours before I started trying to remove the bolts.  I also used a torch to apply heat on the second side.  Of the 8, I had FIVE bolt heads twist off.   In retrospect, I should have hammered on the bolt heads a lot more to knock them loose, used a lot more heat (but I was worried about the rubber at the rear subframe mount) and gone slower but I don't know if it would have changed anything.

 

So, there I am with 5 broken bolts in the subframe mountaing holes and none of them were the ones with exposed captured nuts....awesome.   So, I read forums and learned that most people strongly recommend against try to use extractors in this case since the back of the bolt is rusted and you are likely just going to end with having to drill out a hardened broken extractor.  So I ordered a 5/16-24 helicoil kit and proceeded with center punching the bolts and drilling them out.  This has been a nightmare!!!

 

I've broken off more drill bits in the last 24 hours than in my last 40 years!   I'm still not quite sure why - either it is when the edge of the hole reaches a different metal type (I'm hitting the nut instead of the bolt?) or a piece of a drill has gotten stuck back inside the space behind the subframe and is grabbing the drill bits?   But I've managed to extract enough of the drill bits (or push them through) to get the first hole tapped, the second one is drilled to the right size for tapping and I'm working on the third.  

 

Questions:

 

1). Should I just be dropping the subframe at this point?  I watched some videos of that process and determined that it is quite a bit of additional work and I'm likely going to end up with broken subframe bolts so I was thinking I should avoid it if I can (and it seems feasible).

 

2) Should I helicoil or just drill and retap the existing hole.  I'm leaning towards re-tapping because I don't know if there's enough material or depth there for a helicoil and I think I'm going to break more drill bits trying to get the holes big enough for helicoil?

 

 

Here's what I've learned and I'll add to this as I move further along:

 

1) Go really REALLY REALLY slow with everything.  The metal seems to want to gum and grab every step of the way.  I've used a ton of lubricant and learned to keep my drill speed so slow that I can stop before it grabs and breaks the bit (most of the time).  This means incredible patience (get a good book on audio).  

 

2). Go very incrementally slow with the tap - like a quarter turn or less and then clean the tap.  Repeat.  I broke the end of my tap off on the first turn - I've never seen anything like this.  I think it must be the effect of the hardened nut material????

 

3). Although I saw more than 1 person saying use a helicoil, I'm not convinced that is the right call in this case.  Since these appear to be captured nuts, they may not have enough material for a helicoil.    I may be wrong here and will change this if someone has information that disagrees?

 



#2 cal844

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Posted 22 March 2020 - 04:09 PM

The issue with drilling and tapping is that you need to drill it square

#3 MatthewsDad

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Posted 22 March 2020 - 04:17 PM

Had the same problem in the past. Bit of a nightmare. I helicoiled the threads in the end, and happy with result, but having recently worked on a similar problem on an MG my advice would be to drill the bolts out with progressively larger bits. I started at 1.5mm (tungsten carbide steel) and gradually increased the diameter of the bit, drilling slowly, checking frequently, and using lube oil as you suggest above. Needs to be very accurate and straight.
The initial hole you punch for the first bit has got to be on centre, otherwise you end up going off target and drilling the female thread. If you're lucky what remains of the bolt will eventually fall out without the female thread bring damaged.

#4 Stu1961

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Posted 22 March 2020 - 05:00 PM

Had a similar problem but eventually managed to get them all out with a combination of Plus Gas and heat, lots of heat. Initially I used a blow lamp more suited to stripping paint and struggled then bought a blow torch which I think plumbers use manufactured by Rothenberger worked a treat I was able to apply lots of heat very quickly, once out I ran a tap through the captive nuts to clean them up.

 

 

https://plumbingsupp...lding-plumbing/



#5 Avl_Paul

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Posted 22 March 2020 - 06:59 PM

Had a similar problem but eventually managed to get them all out with a combination of Plus Gas and heat, lots of heat. Initially I used a blow lamp more suited to stripping paint and struggled then bought a blow torch which I think plumbers use manufactured by Rothenberger worked a treat I was able to apply lots of heat very quickly, once out I ran a tap through the captive nuts to clean them up.

 

 

https://plumbingsupp...lding-plumbing/

Many thanks Stu!  Your response gave me the confidence to try drilling out the hole a bit larger and fitting a Helicoil and it totally worked.  That's not a LOT of threads for a helicoil but probably more secure than just tapping the the metal itself with 5/16-24 tap.  AND YOU TOTALLY saved me $$ and time as I was going to need to order a new tap as I only had 5/16-18.   Thank you!  This is why forums are such life savers these days.

 

 

Stay safe everybody.  2 holes fixed -3 to go!



#6 sonscar

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Posted 22 March 2020 - 08:57 PM

I probably would have drilled it and tapped for a larger size,possibly even metric.This would appeal to me as it is cheap to do as I would already have the equipment.This would also give the next owner something to castigate the "dumb previous owner" about.Well done with your tenacity,Steve..




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