A trick to removing stripped Allen-key bolts can be a game of 0.003 inches

recently, I described my gamble of Buying Back Bertha, which may sound like the entitle of a comedy but centered on repurchasing the 1975 BMW 2002 that I had sold to a friend closely 30 years ago .
While it was exciting getting the car running well enough to lurch it from the backyard garage where it had been languishing, it was barely the begin of the hard make of mechanical resurrection. early in the process I discovered a solution to a common trouble : trying to remove strip Allen-key bolts .
Bolts with recess Allen-key heads, besides called hex-key heads, are used in many applications, particularly those where it would not be possible to fit a socket around a traditional hex-head thunderbolt. such is the case with the brake rotors on a BMW 2002. The rotors are attached to the backs of the hub, which is already inconvenient because it means that in regulate to replace the rotors, you have to pull the hub off, which means temporarily removing the wheel bearings. once a hub and rotor are off, you turn them over and lay them on the floor and access the four 8mm Allen-head bolts holding the rotor to the binding of the hub. The bolts are in a thick narrow recessed cavity, which is precisely why Allen-head bolts are used ; there ’ mho not enough headroom to get socket around a standard hex-head bolt .

The brake rotors on a BMW 2002 are held onto the hub from the back by four Allen-head bolts. Visible in this photo are the ends of the threaded bolt holes. The bolt heads are on the other side of the hub. To access them, the hubs/rotors first have to come off.
In my opinion, one of the primary reasons to own an impact wrench, either electric or air-powered, is to remove Allen-head bolts. Clean out the hex fix in the bolt mind with a little screwdriver to remove any coat soil, insert the Allen-key socket, tap it with a little malleus to be sealed it ’ south fully seated in the hole, squeeze the trigger on the affect wrench, and whacketawhacketaWHEEE—out it comes without any drama. An extra benefit is that, because the affect wring zips the bolts out, there ’ s no want to immobilize the thing the gobble is in—in this case, the hub and rotor—to keep it from turning, as you ’ d have to do if you were simply using a ratchet wrench. The affect wrench method is so reliable for Allen-head bolts that I rarely even pre-soak the threads in penetrating vegetable oil or heat them with a flashlight .
But there ’ s a provision. Yes, it ’ s so easy that it ’ second about cheating… provided that you don ’ deoxythymidine monophosphate skip the dance step of cleaning the hole and tapping the socket to seat it. Because if you do skip that pace and squeeze the trigger of the affect twist when the Allen moment international relations and security network ’ deoxythymidine monophosphate in full seated, it ’ ll strip that hex trap in a New York second .
And that, of course, is precisely what happened. While replacing Bertha ’ sulfur left rotor, I dutifully cleaned the bolt heads, but when I did the right one, at some point I felt like I was home plate free, and I got sloppy. Without realizing it, I just stuck the Allen-key socket into the impart hole without first cleaning it or seating the socket. I pulled the gun trigger and instantaneously knew that I ’ five hundred stripped the hole. Of course I cleaned it and seated it and tried it again, but the damage already had been done .
In my first book, Memoirs of a Hack Mechanic, I have a chapter on “ Stuckness, ” and go into a fair amount of contingent on the things you can try in situations like this with either traditional hex-head or Allen-head bolts before you give up and resign yourself to the method acting of survive recourse, which is drilling out the bolt. One of the things you try is interleaving the next largest socket size from a set of both English and Metric sockets. That is, if your stripped Allen headway is 6mm Metric, try a 1/4-inch Allen head socket, as a 1/4-inch is just slightly larger than 6mm. ( For a abscond oral sex, you ’ five hundred try one size smaller, preferably than larger ). You can besides try using Torx bits or sockets and seeing if they ’ re just the right come larger or smaller. then you heat the fastener cherry red with a MAPP boast or oxy-acetylene torch, hammer the right-sized Allen-key socket into the bolt fix ( or the right-sized socket around the bolt principal ), and try again with the impingement wrench. And this time, you do throw penetrating oil, heating system, wax, everything you have at the threads, because you ’ ve got only one shoot at it .
unfortunately, when I tried this on the thunderbolt I ’ d stripped holding the rotor to the hub, I found that 8mm is basically the same as an english size ( 5/16 inches ), and the future size up in either set is excessively big of a jump to fit in the hole, even if you get the heading hot and hammer on the socket .
then I had an theme. I could shim the undress Allen key hole to make up the dispute between its fresh ( stripped ) size and the size of the Allen key. I remembered that I had some 0.003-inch shim stock ( find it on the McMaster-Carr web site hera ) that I ’ five hundred bought to fit an English-sized fan on a motor whose quill size was Metric. I cut a piece, and rolled it into a minor cylinder .

A piece of 0.003-inch shim stock cut and shaped to fit the stripped Allen head hole (left)
then I cautiously placed the little cylinder into the stripped hole, test-fit the Allen-key socket, verified that the shim material did indeed take up the squelch, took the shim out, heated the bolt head with a common mullein, put the shim back, and tapped the socket in identify with a mallet .

The shim stock and Allen-key socket biting into the stripped hole
I then heated the threads with the blowtorch, applied some wax ( Goodson Oil Gallery Wax Sticks, available here on Amazon—way better than penetrating oil ), attached the impingement wrench, prayed to The Automotive Powers That Be, and squeezed the trigger .
Out it came .

The shim stock and Allen-key socket biting into the stripped hole.
In this case, failure to get the fastener off wouldn ’ metric ton have been the end of the earth. It was only holding a BMW 2002 ’ s front rotor to its front hub, and both parts were already off the car. These parts are neither rare nor expensive. And I was doing this because I was about to throw the old rusty rotor into the recycle bin anyhow. But I hush wanted to try .
When working on honest-to-god cars, joy can come in many forms. It can come in the recognition of a solution to a trouble. It can come in the successful execution of that solution. It can come in fixing something with your own hands. On this day, all three were delivered by a little nibble of 0.003-inch shim broth.

* * *
Rob Siegel has been writing the column The Hack Mechanic™ for BMW CCA Roundel cartridge holder for 30 years. His new reserve, Just Needs a recharge : The Hack Mechanic™ Guide to Vintage Air Conditioning, is now available on Amazon. You can holy order a personally autograph transcript here .

reference : https://thaitrungkien.com
Category : Tutorial

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