rcnats

My Feedback: (56)

I have a brand new Zenoah G38. I was removing the screws to replace the stock mount for a cup mount. There are four screws: two in the case and two in the cylinder. I removed both case screws and the Right cylinder screw. As I was removing the Left cylinder screw the top of the screw came off! I looked in horror at a sheared off screw in the cylinder. I calmly got my screw extractor set from my tool bag, put the removal screw in my drill press, mounted the engine in the vise and slowly started the drill. That part was good. Now as I'm inserting the removal tap it breaks off inside the sheared off screw![:@] HELP!!! Any ideas, suggestions??? (Yeah I know, looks like I'm screwed )

captinjohn

I do not know...but I have the same happen on a exhaust bolt. I do know a tap can be burned out with a special high frequency arc...kinda like a electric welder would have. They had a outfit like that in the salvage dept where I worked. It works good if you can locate a place that has one. Capt,n

rcnats

My Feedback: (56)

Thanks for the comments captinjohn......sounds like I need to start checking the yellow pages[&o]

earlwb

Well, the only thing I did, without resorting to the special spark metal removing or EDM machine, was to use some nitric acid to dissolve the screw. The acid dissolves the screw but leaves the aluminum alone. Some other guys say sulfuric acid works too. What I did was build up a wax dam and barrier around the hole with the broken screw in it. Then I would slow drip in a little nitric acid and let it do its thing, then slowly drip in more acid as the screw dissolved. I saved a couple of really expensive aluminum parts that way too. You have to do this outside with a decent breeze going as the fumes can be dangerous. You need to test the acid on a safe spot on the aluminum first to ensure that the alloy doesn't have something it it that reacts badly to the acid. But usually aluminum forms a hard oxide layer on the exposed surface that is resistant to acid, so it doesn't harm it.

The easy out or drill bit is extremely hard, so you can't drill on it to get it out. Although you might get lucky with some carbide end mills that fit down into the screw hole. It depends on how hardened the easy out is.

Another method is to weld another screw or bolt onto the screw. It gets much harder to do as the bolt gets smaller though.

Some other threads http://www.shopfloortalk.com/forums/...php?t-186.html

more ideas:
Another method is to use Alum in a hot boiling water solution
like they detail here: http://www.musicmedic.com/info/articles/num_34.html
You put non-ferrous metal with broken taps
into a saturated solution of Aluminum Sulfate at 120+ deg F. Let it work
a few hours. Or you can just throw it in a room temperature for a few
days and the iron will go away. Only good for NON-FERROUS metals and
make sure there are no other iron pieces on the workpiece. Use a plastic
tray too. Tupperware works fine.


Another method for removing things like a broken tap or extractor is to use a EDM machine (electrical discharge machine). it shoots a spark at the item in question to burn off tiny bits of metal. After it drills into the tap, bolt or exrtractor, you get a thin leftover shell that you can pick out of the hole.

Another low tech method that works on studs that aren't frozen into the engine block or something, is if the end is sticking out slightly, you can weld on a bolt to the end and unscrew the broken stud.

rcnats

My Feedback: (56)

WOW! That's some heavy duty information. I'll check the local machine shops to see if one of them can assist me. If not, how much do you charge?

captinjohn

Hey...that is some awsome imformation....thanks very much...twist them off John !

s3nfo

My Feedback: (14)

Here's one I didn't think of while we were doing email, can you cut a slot across the top of the screw with a cut off wheel deep enough for a screwdriver without going through the case? If so, cut the slot, put the engine in the oven at about 200 and let the case warm up and the aluminum case should expand more than the bolt, hopefully making it loose enough to remove with the screwdriver.

CK1

My Feedback: (60)

try these tap extractors, they dont always work perfectly , but they have saved me more than a few times.
https://www.kimballmidwest.com/Catal...ex.aspx?p=3205

av8tor1977

My Feedback: (6)

I had a very similar thing happen while working on a Volkswagen engine. It was a fairly rare and expensive Type 4 engine, and I was drilling and tapping the block for screw in plugs in the oil passages instead of the stock press in ones. I was in total horror when a 3/8" tap suddenly broke off in the engine. I tried every trick I could think of, but I couldn't get it out.

Finally, I got some beers handy, my cigarettes, and got very comfortable. Then I spent the next 4 solid hours with a Dremel tool, grinding down through the hardened tap until it finally fell apart and I got all the pieces out. A carbide cutter won't do it, you need to use the small round stones.

AV8TOR

earlwb

That is a lot of beers to drink in four hours too.


Yeah I was thinking after I wrote that, that the carbide cutters would not be hard enough.

I always dreaded drilling and tapping a large number of holes, as when you get to the last few, that is when the worst happens. I usually stop for a while, get all comfortable so I can give it 100% attention and go extra slow and cautious.

rcnats

My Feedback: (56)

Here's my current situation: After the extractor tip broke off I leveled it off with the surface (so much for cutting a slot with my Dremel [:@]). I'm checking with the local machine shops. I'll keep everybody posted. Thanks!

captinjohn

Your engine had a 3/8 tap break....how small can you go and still have the small round stones work. I wonder...can it be done on a Supertiger .75 exhaust bolt?

Thanks Capt,n

3136

That's the best advice in the entire history of rcu !

Good luck with that bolt rcnats.
I learned a few good tricks from this thread.

rangerfredbob

My Feedback: (13)

instead of stones I'd use diamond cutters, I've gotten several of the cheezy $7 12V harbor freight rotary tool kits that come with a whole bunch of the diamond bits and have found several uses for them, like drilling a hole half way through my windshield to stop a crack from continuing across the window... and when converting to a different wheel type on my 1/5 scale car I had to drill holes for pins in the hardened rear axle stubs, lubed up an 1/8" diamond bit and drilled on through. Most of them have abrasive at the tips so they can drill straight in, and a bonus is they don't wear out near as bad as a stone

av8tor1977

My Feedback: (6)

I should have specified, it was a 3/8" pipe thread tap; a good bit bigger than a standard 3/8" tap, and a heck of a lot of hardened material to grind through! The real problem is when you break a drill bit, tap, or "Easy Out" off because they are high carbon steel, hardened, and all but impossible to drill out. If you can't get ahold of them mechanically, you have to grind them out. For drilling out bolts, the only trick is to be able to start dead center, and dead straight, so that your bit doesn't wander off into the softer aluminum....

AV8TOR

frequent flyer

My Feedback: (6)

I had taps break in the ends of harden shafts I was threading. Igot them out by buying a solid carbide drill bit and drilling them at a very slow feed rate in my lathe. Hand feed in a drill press could work for you but take your time or you'll snap the bit. use lots of oil  or cooling fluid too.

bigfoot3387

My Feedback: (48)

heat it up litly tap were it broke with a small chizle, ive got screws out of alu were you could barly see them wile hot wd 40 on it take sharp screw driver and drive in the center,no difference than getting a head screw out of a nitro motor,sometimes you get lucky and hard just breaks up,a shop mite charg you more than your willing to pay

willig10

Quit jacking around with the engine. Either send it to Zenoah for repair or better yet send it to Antique for repair. If you dont know Antique do a forum search for him. Best advice you will receive trust me on this

captinjohn

I agree...if you have a Zenoah, send it to Antique...Zenoah engines are his special trade. He knows them in & out ! Capt,n

flycatch

My Feedback: (26)

Sounds like scrap metal.

Charlie P.

Never give up!

You can sometimes shatter a broken off tap with a carbide punch; though I don't know if it would work on a small one.

airraptor

My Feedback: (66)

also never put a screw extractor in a drill press. What were you thinking?

hsukaria

Doggone machinists!!!!! You should go back to LEGO's.

buchtes

My Feedback: (7)

yes it can be fixed. Find a machine shop or someone who has a Mill and remove it with a carbide 3 or 4 flute e-mill, slow speed and lot's of coolant. A good machinist can work wonders.

rcnats

My Feedback: (56)

Update:

Well I found a machine shop and their first attempt was some "tricks" that did not work. [>:]Now it's scheduled to go on a lathe. I'll post the results as soon as they call me. Thanks for all the input!