Removing a broken screw

[Jerry Reider]

I found a broken off 4-40 motor mount screw on my 38 Special today.  Problem was the 38 has blind mounting nuts and the screw was broken off about an 1/8" below the surface of the motor mount beam.  I took a scriber and was able to turn the screw out enough so that I was able to grab it with my fingernails and remove it.  It was pretty easy to do and didn't take but 5 minutes to get out.  I removed the engine before doing this of course.  A side note on screws.  I've been using Allen Screws for my motor mount screws.  The Allen Screws are aircraft grade 8 screws as opposed to the slotted screws which are I'd guess are made of lower grade steel.

[Russell Shaffer]

That is a problem with selecting bolts and screws.  The grade 8 stuff is very tough and strong, but they will break.  The hardness makes them brittle.  The soft, cheap ones are not as strong and won't take as much torque, but they tend to bend before breaking.  A good compromise seems to be grade 5 at least in larger bolt sizes.  Good idea about the scribe - dental picks will also work. 

[john e. holliday]

I don't know what grade they are, but, I get my screws by the bulk from  RTL Fasteners.   DOC Holliday

[don Burke]

A common misconception is that Allen screws are aircraft grade 8.  They are case hardened to a similar tensile strength but as noted are far more brittle than aircraft grade 8s.  A/C grade 8s are not commonly available in smaller than #10 shank diameter.  Though I'm sure one could find an aircraft spec for smaller screws but finding and buying them would be a different story.

Allens are probably the best bet for tensile strength in sizes we use, just don't overtighten them.  And don't run the engine with the screws a little loose, that'll pop the head off right away!

[Charlie Pate]

A common misconception is that Allen screws are aircraft grade 8.  They are case hardened to a similar tensile strength but as noted are far more brittle than aircraft grade 8s.  A/C grade 8s are not commonly available in smaller than #10 shank diameter.  Though I'm sure one could find an aircraft spec for smaller screws but finding and buying them would be a different story.

Allens are probably the best bet for tensile strength in sizes we use, just don't overtighten them.  And don't run the engine with the screws a little loose, that'll pop the head off right away!

A fellow I new that ran (owned ) an IHRA funny car found the exact thing about allen head screws,bolts.
           He sold auto parts!. Once again the deadly assumption. 

[Mark Scarborough]

FWIW Aircraft hardware is not grade 8. it is much more resilient than grade 8 bolts are. As stated the grade 8 hardware is by comparison stronger, but more brittle.

[Rob Killick]

Hi ,

A good set of left hand drill bits can be a God send , for removing broken studs or bolts .
Personally , I'd go with stainless socket head (Allen head) capscrews , as they are more forgiving when you have a rough landing and want to save your motor's lugs , mounts , etc.

Rob K.

[Jerry Reider]

Sounds like some good suggestions on hardware selection.  Actually, a carbide tipped scriber would have worked better than the HSS scriber that I used.  Carbide seems to get a better bite on the surface of the screw because it's harder.

[Clayton Berry]

I saw maybe three broken 4-40 socket head screws at the Huntersville contest earlier this year.  Dunno what the deal was.  Over-tightened?  I get 'em off the shelf like many folks, I guess.  Brodak label, I suppose.  And don't recall breaking one ever.  Not even my dad's old supply from the sixties.  Well, there was that time in Norfolk.  Alas, it also broke the case on my ST 46.  Can't blame the bolts.  Me, I blame the wind.

I used to ride British motorcycles, and learned the value of Loctite.  The blue stuff.  The red stuff is only good for cranks and anything else you never ever want to get apart.  I like to put things together reasonably clean, with a bit of the blue stuff.  It wicks a little, and will come apart with a little effort.  But, vibration isn't usually a problem.

Then again, I'd have used plastic explosives to get that screw out.  After removing the bellcrank and pushrods and stuff.  Can never be too safe around model airplanes, you know.

I have a book around here on fastners, actually.  Fascinating book.  A guy named Carrol, if I remember.  Built race cars, but much info on all sorts of fasteners.  Obscure stuff, counterfeits, military specs...  Fascinating.  I had no idea there was as much put into little ol' nuts and bolts.

Someone ask me sometime about the motorcycle trailer, the grade two bolts, and the ne'er do well neighbor kids when I lived in Sterling.

It ended with me saying that if they were ever asked if they lived next door to a crazy ************, you be sure and tell them that you do.  Because you do!

Gads.  I'm starting to believe my own BS at this point.

[Steve Helmick]

Most the socket head machine screws you find these days are made in China. Some might be ok. Or not. If we have to start making this sort of stuff again, I'm afraid we'll be in deep stuff of another kind.  Steve