Lessons learned with exhaust studs

[lukehan]

This is mainly to vent my frustrations of the past couple of days and to share what did and (unfortunately) did not work. I am in the middle of a multi-year rebuild of a 79' GS850. This past weekend I decided to try and get the cylinder head in shape. It was basically ready to go minus the 7 (yep you read right) snapped off exhaust bolts. I went to the local bike guru and being a one man operation didn't really have time to work on it much, but did help out with one tip, most of them that snapped off did so leaving 1/4" or more of thread out of the head, so he threaded on new nuts and welded them in place, now I had "new" bolts to try again. I was able to get two of them out with an air impact, set on its lowest setting and short bursts in both directions. Ok, 5 left. I decided to try drilling the rest. Starting with a small bit and working my way up. KEY POINT- getting the bit centered. Since there was some of the bolt still above the surface, I took a file and carfully filed the top of the bolt flat, this helped tremendously with getting a good center punch and keeping the bit from walking. I got all of them drilled out to about 2/3 the diameter of the bolt and thought "I guess I could try and easyout" if you have similar thoughts, banish them from your mind. I will never use an easyout again. Even after the heat/lubricant/wax technique, you guessed it, SNAP, flush with the bolt/cylinder head surface. Long story short, I was able to drill out and retap all the others with no further problems, but the one with the easyout is my downfall, I'll have to take it to a machine shop, still, one is better than 7. Also to assist with the drilling, I constructed a jig to hold the head, basically sandwiched the head in a U made of 2x4's and plywood with wedges cut and glued underneath to adjust the angle so it could sit on the drill press shelf so that I only had to worry about keeping things centered. I have tried drilling the easyout with a cobalt bit, but it keeps catching on the softer metal around it and walking off center. I guess these things keep us humble. I hope this helps someone out there from grief. To sum up (sorry for the length) never use an easy out, other methods are much faster, easier and if you mess them up are not as hard to fix (screw up drilling out and retapping you can still helicoil or go to the next size up in threads).

Luke

[Wingnut]

I have walked in your shoes, except I broke off a drill. Similar.

An old farmer told me to use a good quality center punch and chip the drill to pieces. The drill is hard and will shatter near the edges. This worked on a drill, don't know if it will work on an easy out.

But, if you have torches you can melt the easy out and blow it out with oxygen.

[ptm]

You might try a very small carbide bit http://www.dremel.com/productdisplay...5&Color=009999 in a Dremel. I don't know if there's enough room to work. Using a flexible shaft might get you in closer. Even if you can't grind it all the way out, it might make enough of a dent in it to keep the cobolt bit from wandering...

[lukehan]

I might try the dremel tip, it is fortunately on a fairly accessable part, it is the most outside of the bolts, closest to the edge of head. I guess one more trip to the hardware store won't kill me.

Luke

[Footy.]

The best and most reliable way to remove hard broken drills, easy out's etc, is to find someone who has a spark erosion machine.

These very accurately remove metal using a principle like arc welding. I have seen a demonstration where the operator signed his name in the shank of a tool steel tap, the lines `written' were about 1mm wide and went right through the tap!

If you search or phone around your area, you should find someone who can do this.

Being in the trade, i regularly drill out broken studs, mostly exhaust studs! The so called `easy outs' are a big `no no'!!

Far better to drill the `whole' stud out, and repair the thread with a Helicoil or similar. You will rarely drill acurately enough to rescue the original thread anyway.

Footy.