Broken L24 rear cylinder head stud - Tips wanted for drilling & tapping in situ

[Namerow]

Bonzi Lon's comment about watchmakers using this technique got my attention, so I did a little internet searching and came up with a site dedicated to watchmakers. 

http://mb.nawcc.org/showthread.php?94417-Removing-broken-screws-with-Alum-bath&s=9a54a148536c988626245b769919efd8

Here's a good summary comment from one of their members:

"Alum is pretty danged safe stuff, and one of the safer things to get steel out of brass or aluminum. In other uses, it's used in heavily-silted water to flocculate (clump) the silt so it'll settle, and it also disinfects the water somewhat. My uncle used it to treat his tan-colored well water way up in the Colorado Rockies; a few cupfuls of alum would clear up 350 gallons (over 1000 liters) in a couple of days. It made the water taste a bit funny-sweet, but was perfectly safe. It's also used to make pickles crisper. It's the active ingredient in a styptic stick (used to clot shaving nicks).

As people have said before, it works far faster at removing steel leftovers if it's hot. (WARNING! Don't use a steel pan or can to do this in - it'll eat that, too! Stainless isn't as reactive, but just use glass (Pyrex or its equivalent) or an aluminum pan, ok?) Bring some water to a simmer, and dissolve as much alum in it as will dissolve (saturated solution), toss in the brass or aluminum doohickey with the steel whatzis in it, leave it at or just below a simmer, and come back in "a while" to no more whatzis. It'll still work at room temperature (if you don't want a glass thing on a cooktop, always a valid concern), but it'll take longer (like overnight). The alum reacts with the iron, but not the aluminum or the brass. <geek> According to the chemistry book, it has to do with the trivalent nature of iron (which doesn't exist in copper or zinc). It starts out full of aluminum ions (which are also trivalent), so no reaction there. </geek>

The stink is from the sulfates being ionized and released. If you inhaled enough of it, you'd eventually have a tiny fraction of the the sulfates bond with the water in your mucosal membranes to form a mild sulfuric acid, but your body will make you leave waaay before it comes close to doing any damage. In other words, don't stand and force yourself to snort the fumes, but don't break out the hazmat gear, either. Trust your nose to tell you when enough is enough. Use common sense."

It's evident from the rest of the thread on that site that the alum technique is well known and proven effective -- at least, effective on tiny watch parts. A couple of commenters there speculate that it's especially effective on the threaded areas of a steel bolt -- and that may be true, although probably just because the liquid can penetrate along the threads, where it has a very large steel surface to work on (compared to just the head of the stud).  In general, the watchmaker site commentary expresses full confidence in the safety of this technique for use with steel-in-bronze and steel-in-copper, but nobody steps right up and says they've used it successfully for steel-in-aluminum.

We'll have to wait to see how it does on a a quarter-inch worth of snapped-off 6mm bolt in my aluminum casting.

[Zed Head]

Seems like one of those theory/practice things.  In theory it should work great.  In practice maybe it isn't so easy.  Or, in a commercial setting the dissolved iron in alum solution is chemical waste, requiring expensive material handling costs.  I could see that as an issue.  

Or maybe it's just hard to figure out how much to charge for letting a broken stud sit in a solution of alum.  "Where's the stud you removed?"  It's gone.  Where?  It dissolved.  How much will it cost me?  $50.  $50 for soaking something until it disappears?!  Rip-off!

[Zed Head]

There's probably some thermostat housings out there that this would work for.  Bolts break off in them often.  

A plastic plumbing elbow with a rubber gasket might be a better vessel than an old pop can for a cylinder head stud also.  I'm tempted to go jam an old rusty stud in my spare engine and see how it works in the real world.

[Patcon]

I thought about the thermostat housing too...

[Zed Head]

Didn't mean to jump Namerow's thread but I had too much free time, and I've spent a few hours leaned over the fender working on a broken thermostat housing bolt in a head.  We can compare notes.  Mrs. Wages vs. all comers.  We should at least be able to come up with a simple procedure and things it should work on.