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rear subframe bolt broke - got it out
https://www.ausmini.com/forums/viewtopic.php?f=2&t=42517		 Page 1 of 2
Author:  mickmini [ Fri May 30, 2008 4:17 am ]
Post subject:  rear subframe bolt broke - got it out
bugger :twisted:

short mounting bolt at left front of rear subframe broke the head off when i tried to undo it.

and not a BFH in sight :roll:

have been squirting the remnants with penetrating oil for a week now. cut a slot with the dremel and tried to screw it out. nup broke again. now i have to grind it down to the panel level and probably try to get an easy out type device.

any alternatives?

on the good side, for a 42 year old car, there is only one other spot of rust on the body worth mentioning. about a 5mm diameter hole on drivers side a-panel. i even took the seam covers off for the first time, and no rust underneath all the dirt :shock:

cheers
michael
Author:  drmini in aust [ Fri May 30, 2008 7:15 am ]
Post subject: 
Forget easy outs, they will break for sure if bolt is that seized, then you have a broken hardened tool to get out instead.

Drill it carefully on centre with a 6.9 or 7.0mm drill, then tap out to 5/16 UNF again. If that fails I drill it 5/16", tap it 3/8 UNC and fit a starter bolt.
I've done this many times... it's not that hard.
When you fit new bolts coat them with gasket cement, it stops the exposed threads rusting and keeps water out of the captive nut.

<edited> due to brain fart.. thread is 5/16 UNF, I had UNC....:lol:
Author:  justminis [ Fri May 30, 2008 7:20 am ]
Post subject: 
Why UNC Kev? These were UNF originally. Interested to know.
Author:  drmini in aust [ Fri May 30, 2008 7:23 am ]
Post subject: 
Sorry, typo, I meant retap 5/16 UNF, not UNC.
But if I have to drill it bigger I use 3/8 UNC, it's a coarser deeper thread and less likely to jam up. And a stock starter bolt fits great.

tapping size drill on chart for 5/16 UNF is 6.9mm, but I use 7.0 because I've got one... :wink:
Author:  Hanra [ Fri May 30, 2008 8:27 am ]
Post subject: 
Slightly off topic. I snapped a manifold bolt in the head of my V6 Crummo. Drilled it and put an easy-out into it, snapped the easy out off inside the bolt.... So then had to drill out hardened steel easy-out out then drill bolt out.... Was a very frustrating weekend...
Author:  drmini in aust [ Fri May 30, 2008 8:47 am ]
Post subject: 
Esy-outs are poorly named... :lol:
If it's jammed well enough that it's sheared the bolt or stud off, an esy-out has buckley's hope. :P
I've fixed lots of broken S/S bolts in alloy outboards over the years, salt water + electrolysis really jams them in. The esy-outs stay on the shelf these days. :wink:
Author:  Blokeinamoke [ Fri May 30, 2008 9:01 am ]
Post subject: 
Heat it with a butane torch or similar and then cool it rapidly - repeat several times.

Then cutting a notch in it and drive it in - yep drive it in a quater of a turn and back it out.
Author:  drmini in aust [ Fri May 30, 2008 9:13 am ]
Post subject: 
The problem with subframe bolts is they go right through the captive nut, and the threads exposed inside corrode. So, it's not just a matter of freeing the thread in the nut...
I don't mess with turning them now, I just drill them out and retap. If you get it nicely on centre, the tap will pick up the bolt thread remnant and peel it out.
Author:  richarde [ Fri May 30, 2008 10:16 am ]
Post subject: 
I tried drilling out a bolt on the cylinder head before (thermostat housing bolt) and drilled off centre so it wasn't going to work. So I grabbed the dremel and a smallish grinding bit and ground the remains of the bolt out. It took a while but I got it out with no damage.
Author:  mickmini [ Fri May 30, 2008 6:39 pm ]
Post subject: 
drmini in aust wrote:
The problem with subframe bolts is they go right through the captive nut, and the threads exposed inside corrode. So, it's not just a matter of freeing the thread in the nut...
I don't mess with turning them now, I just drill them out and retap. If you get it nicely on centre, the tap will pick up the bolt thread remnant and peel it out.


Thanks Kev, that is kind of what i was thinking anyway. Now i just have to find a 5/16 UNF tap.

should be able to drill pretty close to centre of the bolt if i punch it well.

where does the inside of the captive nut sit? i tried looking/feeling in the rear of the pocket on the inside, but could not see it. If I had, i was going to try driving it all the way in instead of out.

BIAM, i also thought about the heat method, was even considering zapping it with MIG to give a nice heat shock, but if it goes right through then drilling and tapping is probably better.

cheers
michael
Author:  MiniBob [ Mon Jun 02, 2008 1:10 pm ]
Post subject: 
mickmini wrote:
drmini in aust wrote:
The problem with subframe bolts is they go right through the captive nut, and the threads exposed inside corrode. So, it's not just a matter of freeing the thread in the nut...
I don't mess with turning them now, I just drill them out and retap. If you get it nicely on centre, the tap will pick up the bolt thread remnant and peel it out.


where does the inside of the captive nut sit? i tried looking/feeling in the rear of the pocket on the inside, but could not see it. If I had, i was going to try driving it all the way in instead of out.

The captive nut is inside the closed section of the subframe.
Unfortunately while trying to do all this on my car, the welds gave up and the nut fell off inside the subframe box section. Ended up making the hole larger to get it out, then welding a new nut to a washer and welding the washer in place. :roll:
Author:  marcello [ Mon Jun 02, 2008 2:50 pm ]
Post subject: 
i once managed to plug weld a nut to the end of the broken bolt. it worked really well. you need a bit of exposed bolt though. could be worth a try if you can.
Author:  mickmini [ Tue Jun 03, 2008 4:15 am ]
Post subject: 
Got it out!

patiently drilling, going up in size and checking that i had not drilled so off-centre as to drill th thread away. using a 17/64" bit, which was my last size to avoid the thread and the bolt remnants just unwound up the bit :lol:

so i thought to clean the thread i could send off for a tap, tap wrench and postage or i could grab a high strength bolt i happened to have sitting there, taper it, slot it and see what happens when i screwed it in.

a little WD40 and it worked a treat. now i can screw a bolt in that tightens up properly, and i can see good thread when i stick my penlight in there. 8)

a couple of pics of tool and remnants .....

Image

Image
Image

cheers
michael
Author:  d1ck0 [ Tue Jun 03, 2008 7:12 am ]
Post subject: 
Well done!
Author:  sitnlo62 [ Tue Jun 03, 2008 7:39 am ]
Post subject: 
Good work Michael,
A little Antizeize on the thread when reassembling will make it easy to get apart next time. Maybe in another 30 years or so!!!
Dave
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