30 May 2009

Removing a broken stud

This doesn't look like much, but to me it's a work of art. You see life is not all fun and games. Sometimes you have to fix the mundane tools we take for granted every day.

The truck has had a broken exhaust stud since before I bought it in 1995. Until recently the resulting exhaust leak would seal up within a few seconds after starting. However last year the gasket blew out. I've dreaded this job knowing that a steel bolt in an Aluminium head has probably corroded itself together over the last 14 years. Also the job is easy to screw up, turning the head into 30 lbs of scrap Aluminium.

Removing a broken stud requires drilling a hole down the middle of the stud then inserting a bolt extractor and unscrewing the broken part. The rub is the hole in the stud has to be drilled straight into the stud and not veer off into the softer Aluminium of the head. Also the break tends to put a peak in the center of the stud, which pushes the drill off to the side. The installation in the vehicle prevents getting the drill near the hole which will allow the drill bit to wander, again off the stud and into the soft head.

The trick is to use a drill guide. This keeps the drill bit centered on the stud. I didn't have one but was able to make one from a section of 1/2" steel rod. The end was ground into a cone to fit the hole. It worked perfectly. I held the guide on the hole with my fingers and used a long shank drill to start the hole.

Once the top of the stud had nice Vee started, A counter clockwise cutter was supposed to dig into the face and twist out the stud. In this case it was cutting nicely but not digging in. A couple taps of a hammer set it into the stud and next thing you know it was out on the floor!

update: Looking back at this article reveals a glaring omission. Considering the time the steel broken stud has been the Aluminium head (>14 years), dissimilar metal corrosion is always a problem. A penetrating oil can ease the removal. I sprayed it liberally with Kroil. I don't know how much it helped, but would guess it's in the 10-40% range. BTW, the one can I have will probably last lifetime.

Dang.. If their offer of 2 cans for $12 including shipping is legit (I don't know why it wouldn't be, but I didn't read the fine print), that's a screaming deal. My one can with shipping was nearly $20. Give the other to your favorite son or a friend!

(Standard disclaimer applies, I have no commercial interest in Kroil nor Kano labs, I'm just a satisfied customer. I bought my can, they didn't pay nor solicit this mention. A penetrating oil won't do the work for you, but it will make the work easier.)


David aka True Blue Sam said...

Nice Save! Broken studs always gave me a bad feeling in the pit of my stomach.

Anonymous said...

I was a millwright for a few years, you did well. Congratulations.