How have you fixed twisted off rusty bolts?

[Mikes Z car]

Hi all,

What have any of you done to repair rusty bolts that twist off? My twisted off fender bolt (passenger side):

I had a lower fender bolt twist off on both sides of the car, the front bolt on both sides. Each side has two bolts at the bottom. After drilling out the old 8MM bolt on the driver's side I bought a helicoil but the tap that came with it broke off when tapping the new threads probably because I didn't know to back it out frequently to clear the shavings.

Broken off helicoil tap:_________Close up view:

The easiest way to fix this I guess would be to ignore the twisted off bolt and put in a large #12 self drilling screw (AKA tech screw) with a washer right next to the twisted off bolt to hold the fender on if the sheet metal is solid. Or use (shudder) a moly bolt if the sheet metal isn't that strong. Has anyone else had to fix a twisted off bolt in an inaccessible area? How did you fix it? This is how I am fixing my twisted off bolt:

After the nut is welded on the bolt will be removed and the tab bent back up flat with the body of the car where it was in the first place.

Edited September 10, 2013 by Mikes Z car

[siteunseen]

I broke a bolt extractor getting a broken exhaust stud out from under the thermostat housing on the head. A drill bit wouldn't even scratch it so I had to get a bolt welded onto it too then it backed out with the remnants of the old stud with it. A lot of trouble but that's the only way.

[ajmcforester]

Use penetrating oil hit it several times for the next day or two and see if yo can twist it out. next drill the tap out. I weld a new nut to the panel the replace the bolt. This way it all matches. I would not use a self tapping screw

[Mikes Z car]

siteunseen,

I hadn't thought of welding a nut onto the extractor, thanks for the idea. I wound up cutting open the body and cutting off the nut from the back. The angle grinder cut off wheel went through the hardened extractor metal it just took a little while. After that to get off what was left of the nut I used the angle grinder with a grinding wheel on it. It made lots of neat sparks. Some of them got on me.

ajmcforester,

I only thought of the self tapping screw as a cheap easy solution but didn't like the trend away from originality so went with welding a new nut on. When I am done it will look original except for the zinc colored bolt.

[madkaw]

Try modifying an old flat blade screw driver or something that will grab the open slot areas between the tap cutting blades. It should back out with a little work and determination. I doubt you will be able to drill the tap as stated earlier.

If you wind up not using that hole, I would suggest a riv nut instead of a sheet metal screw

[Mikes Z car]

I hadn't thought of modifying a screwdriver either. Well I get another chance on the passenger side, I got a new tap in the mail yesterday to do that side with.

[Patcon]

Dip the new tap in cutting oil or motor oil and don't force it. It will cut better if lubricated and they are very hard which tends to make them brittle. As you have found out they don't bend they break. If the other bolt breaks in the other rocker drill it out and even if the hole gets a little off center or a little too large as long as the tap has something to bite it will cut new threads. If the new threads are not full depth just don't over tighten the new bolt so as not to strip them. Also this is a good location for anti-seize... also I have found if you use too much force on these hidden nuts you can actually break them loose from the panel which is also a pain...

Charles

[Mikes Z car]

Thanks Patcon,

Thanks for the info. Didn't know the nuts can break loose! What have you seen done to fix hidden nuts that break loose? The anti seize is a good idea. I might spray some anti corrosion on the inside sheet metal too though I don't want it too close to the work if I have to weld it.

Mike

[Patcon]

If I break a hidden nut loose the only good fix is like you did where you get access to the back and weld it back on...

Charles

[EuroDat]

That is a good fix Mike. I can not think of a better way to do it. Also gives you the opprotunity to treat the inside.

Getting out a broken off tap is no easy job. A lot of force to break it off, so you need just as much or more to get it out.

Chas

[Hypertek]

Think it might be a good precautionary idea to have a propane torch and penetrating fluid to soak and heat up the surrounding areas before attempting to unscrew?

[Mikes Z car]

Someone should write a book on various repair techniques. I don't think I have seen a book like that anywhere.

I probably should have tried the propane heat on the passenger side bolt. Anyway I wound up drilling that bolt out like I did the driver's side bolt. I hope this weekend to carefully tap that passenger side hole to avoid breaking the tap by backing it out frequently. I have the helicoil for an 8MM bolt ready to put in the hole. I am a lousy welder but on the driver's side it seems I got the nut welded on to the sheet metal and the sheet metal pushed back into position and welded back flat with surrounding metal . That was fun! Doesn't take much to give me a feeling of accomplishment.