Broken exhaust stud farmer fix

[SIR REAL ED]

You old farts who grew up without machine tools probably know all about this, but some may not.

In any event it is a cheap fix (WG content).  Drilling out studs is as old as the hills, the trick is to drill in the center of the stud and drill straight down the axis of the stud.

Four really rusty 8mm exhaust studs.  Using lots of patience, penetrating oil, heat, low torque impact tools, and ye old double nut technique resulted in three studs removed and one stud broken.  Honda really sunk these babies into the head!!!!  16mm of stud engagement length and tapped holes over 30mm deep!!!  The three that didn't break, came out really hard even down the the last few turns.

8mm stud, .25" protruding from the head.  McMaster.com has everything you need!!!!!

So I bought:
-  three 5/16" ID (close enough to 8mm to work) x 1.25" long bronze brearings.
-  one drill bushing for a 1/8" drill with a 5/16" OD x 1" long
-  one drill bushing for a 3/16" drill with a 5/16" OD x 1" long.

Simply "press" the drill bushings into the bearings with a hammer or a vise and fit over the broken stud.  Be patient and use a good machining oil.

The "Easy Out" didn't work even after drilling away the shoulder of the stud which should have released all the axial tension.  So the end result was drilling out the stud with a 1/4" left hand bit which is damn close to the 6.5mm tap drill diameter.

Don't tell anyone I learned this technique from Bigfoot......

[Ncdan]

That sounds like you figured it right close 👍
The only thing I may have tried different would have been soaking it with penetrating oil every day for a few days prior to the attempt?

[SIR REAL ED]

That sounds like you figured it right close 👍
The only thing I may have tried different would have been soaking it with penetrating oil every day for a few days prior to the attempt?

I agree 100%.  I went down that road for 3 weeks!!!!!

That was one of the reasons I wanted to drill all the way thru the stud, so I could get penetrating oil into the cavity behind the stud.

Never saw studs that tight in my life.

[SmithSwede]

I’m not following you about the bearing.  Are you saying you put a small bearing into the bushing?  Why?  So the drill bit could rotate more easily?

Thanks for posting this—I’m all about learning how to do this stuff.

[Tom H]

The bronze bearing is the bronze tube in the pic. It's not a ball bearing type bearing. Same type bearing is used in many connecting rod small end. Also known as bronze bushing.

BTW: Very nice fix! I will keep this in mind when needed!

Tom

[SIR REAL ED]

I’m not following you about the bearing.  Are you saying you put a small bearing into the bushing?  Why?  So the drill bit could rotate more easily?

Thanks for posting this—I’m all about learning how to do this stuff.

You are more than welcome, I don't know much, but I'm willing to share what I know.

The ID of the bronze bearing 5/16" is selected to match the 8 mm OD of the broken stud.  This allows you to find the center of the stud.  5/16" and 8mm are "close enough for govt work."  The 5/16" OD of the drill bushing is selected to match the ID of the bronze bearing.  The 1/8" ID of the drill bushing is selected to match the 1/8" pilot drill bit.  A 1" long drill bushing provides a length 8 drill diameters for alignment to the stud axis.  Longer is better if you got the drill bits to match.  I didn't so McMaster got some more of my money for the two extended length drill bits.  Front downtube of the frame necessitated long drill bits.

Original plan was to drill a 1/8" pilot hole, followed by a 3/16" drill bit to allow the use of a stud extractor after using a 5/16" drill bit to remove the stud shoulder.  But the stud was too tight.  Since all four studs were super tight even when they were half backed out, I suspect a dull tap was used to cut the original threads.

Since that did not work, I used a 1/4" drill bit to drill out the stud since 1/4" is damn close to the 6.75mm tap drill diameter.

Tap drill diameter is always thread OD minus thread pitch.  In this case a 8mm x 1.25mm pitch = 6.75mm = .265".  I could have used a 17/64" drill for a better match, but I wanted a "little cushion."

Some would pick out the thread remnants with a sharp tool, I just carefully used an M8 tap to remove the remnants.  If that proved to be a problem, I would have followed the 1/4" drill bit with a 17/64" drill bit.

I really did not need to replace the studs (after the first attempt showed all four to be tighter than Hell I told myself "Don't be dummy stop now!"  I didn't listen!), but it was fun tinkering, and now I got some cool stainless steel studs!!!!

Another plus was a found I great, new to me, fastener vendor:https://www.belmetric.com

[SmithSwede]

Thanks.  Now that all makes sense.  I’ve saved this for future reference.  I’ve got some super rusted exhaust studs on a Ducati.  If I ever have to take the exhaust headers off, it might well turn into this kind of drama

[SIR REAL ED]

Thanks.  Now that all makes sense.  I’ve saved this for future reference.  I’ve got some super rusted exhaust studs on a Ducati.  If I ever have to take the exhaust headers off, it might well turn into this kind of drama

You are welcome.  If it comes to that, I hope it helps.  Penetrating oil and a propane torch can save a lot of work.  Just be patient!!!  Any time you find yourself wanting to rush the job.... just think about taking the head off and carting it to a machine shop.  That usually slows me down quite nicely.

More often than not, heat and penetrating oil plus a small impact tool will do the job!

I've actually sprayed studs or bolts or spark plugs with penetrating oil one a week or so, even if I knew I would not get around to change them for several months.  Can't hurt!

I always make it a point to replace exhaust nuts/bolts with stainless steel nuts/bolts and never seize as soon as I get a bike that is new to me.

In one of the Brit bike mags I remember seeing a localized induction heater that looked really handy.  I've meant to research it but never did. 

I would assume a couple geometries would be available.  A male heating coil one could put inside a bore, and a female heater coil one could put around a stud at the minimum.

[SmithSwede]

Yeah, on my new Guzzi V7, one of the first things I did was put copper anti-sieze on the exhaust studs.  And then every time I do a valve adjustment I unscrews and re-screw those nuts to make sure nothing is getting sticky.   Those are a joy and not rusty. 

Not much you can do if you buy an old used bike and those connectors are round and rusty looking!

[SIR REAL ED]

Thanks.  Now that all makes sense.  I’ve saved this for future reference.  I’ve got some super rusted exhaust studs on a Ducati.  If I ever have to take the exhaust headers off, it might well turn into this kind of drama

It wouldn't hurt to start giving them a shot of penetrating oil now each time it crosses your mind.  Just in case you find yourself in a situation where they need to be removed weeks or months down the line.

All the nuts came off my exhaust studs easily.  All the studs were "Don't be stupid.  Leave well enough alone!" stuck.

If you have the space you could also double nut them now, and when the engine is hot (the hotter the better) try to turn them a bit by loosening the inside nut.  It might later make a great story of how you avoided disaster by being pro-active months ahead of the time of the needed task!!!