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Baffle mounting screw broken

L

Loman

Well Known Member
About two years ago, I bought a nice O-320 with 174 hours since total overhaul for my project. I saw the engine run before it was taken off the donor aircraft but I never noticed that one of the baffle mounting screws was broken off. It's the one forward of the No.3 cylinder. When i finally noticed the problem I was pretty confident that I could get it out but the job has gone wrong.

I was drilling out the core of the screw with a #40 bit in preparation for using a screw extraction tool when the tip of the bit broke off in the body of the screw. It broke off cleanly so there was nothing to grab. I used every tool I had today and got nowhere. The steel in the tip of the bit is just too tough for anything I have available.

These holes run through to the first gap between the fins so there is no way of getting at the back of the screw.

2crpydd.jpg


One idea I had is simply to leave the broken screw where it is and drill / tap a new hole lower down in the same boss. there is plenty of space there. However, I would obviously prefer to get the broken screw out

All ideas gratefully received.
 
Might be tempted to drill lower as you noted. The steel you are trying to remove is going to be a challenge. An EZ out works... but not after the screw breaks off. Is that Gorilla Glue on there also?
If it is #3... you might want to read the recent thread about washers and other mods to the baffle in that region for cooling that particular cylinder. I am about to mod mine... so your close up photo brought it to mind.
Sorry you have had the misfortune of snapping the screw off. I am sure there are endless stories among builders who have cursed that same situation many times.
 
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Well, that just sucks. There is little chance that the screw is going to be removed with a screw exctractor. The first question is why the #40 broke. Was it deep and did it break through and snag? If so you "may" have some luck with a center punch, but if that is a blind hole, it will only provide some relief.

if the head is on the plane then a carbide blade bit, or a very small carbide burr on a high speed grinder (dremel) might be able to drill through. If it is off the plane and can be set vertical, nitric acid will dissolve the bit and not harm the aluminum.

Finally, after you get the bit out and screw, your best bet is a heli-coil insert for the final touch. Re-drilling a hole nearby is a very risky proposition. I have done dozens of these on VW's and salty outboard motor blocks.
 
I've had good luck with a Dremel. They make several tungsten bits that will make quick work of the broken bolt and the #40 bit. Keep it centered and bore out enough to get an extractor bit tightly in place.

The bit I used is a Dremel 9904 tungsten carbide cutter. This is a 3/32" bit. They also make the same bit in 1/8". I'd try the small one first.

Best of luck!

Keith
 
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Can you pull #3 and swap it with another cylinder? Sounds weird, but I bet you're already in for that much time.
 
Weld

Take a nut a little bit larger than the shank of the bolt and place it over the broken shank area. Then take a mig welder and weld up the hole of the nut. Take a wrench and turn the offending "new" bolt out! The heat will loosen the broken stud out and if not will at least get your carbide extractor out. Take a piece of metal and tap a hole and break a bolt off and practice if you want to get a feel for it if it makes you uncomfortable but I have done it several times and it works !:eek:
 
A method I have used in the past is to put a small carbide burr in a Dremel tool and then (very) carefully cutting a slot into the screw shank, enough to get a small straight blade screwdriver head into. Then after judiciously heating the area - aluminum expands much more than steel - using the screwdriver to back the piece out. Heat it to where it's hot to the touch but I wouldn't go much further than that. A bit of penetrating oil wouldn't hurt either.

You will need a steady hand to cut the slot - but the carbide burr will cut the hard drill steel very easily.
 
Great replies - thanks and some further info

Those are great responses. I am really grateful to all who contributed.

To answer the points raised:

1. There seems to be a consensus on the Dremel tungsten carbide burr so i will try that first, to be followed by an Easyout screw extractor. I don't fancy trying to cut a slot for a flat blade screwdriver. I am likely to get too close to the threads or else the only screwdriver blade that will fit in the new slot will be too small and puny to turn the screw.

2. If the Dremel burr fails, I might try the "Rescue Bit" designed for drilling out hardened steel such as drill bits, taps and Easyouts.

3. Seems like heat and penetrating oil is a good idea when I get to the stage of making the screw move with the Easyout.

4. The engine is mounted on the plane as I have been working on cowl and baffles. That makes getting the head into a vertical position quite difficult but not impossible. I am fascinated with the idea of the Nitric acid. If it comes to that, the best way of doing it would be to pull that cylinder, leaving the rest of the engine in place.

5. I am not certain what benefit swapping cylinders would be, unless replacing #3 entirely with a new one is what is being suggested. I had already decided to do the washer mod or something similar

6. There is nothing of the screw protruding. In fact it is below the surface of the hole. So I can't tig weld a new head onto it. Great idea though if there was just a little of the screw protruding.

7. How it happened? I had drilled a short hole (no more than 1/16) in the broken screw using my best small bit, which is a Dremel 2mm. I switched to a new 'jobber' #40 to continue. It is slightly bigger at about 2.4mm I was using low speed and high pressure, which I thought was the correct procedure for hard metals. The bit immediately gripped on the hole and snapped off low down. Somebody commiserated with me for breaking off the screw. That was the previous owner, not me. I just made it worse.

8. Drilling a new hole lower down is obviously a last resort and I would pull the cylinder and give it to a professional if that was the only remaining option.

Finally, I promise to report back once I have it solved, which could be soon but could also take a long time
 
Loman said:
Those are great responses. I am really grateful to all who contributed.

To answer the points raised:

1. There seems to be a consensus on the Dremel tungsten carbide burr so i will try that first, to be followed by an Easyout screw extractor. I don't fancy trying to cut a slot for a flat blade screwdriver. I am likely to get too close to the threads or else the only screwdriver blade that will fit in the new slot will be too small and puny to turn the screw.

2. If the Dremel burr fails, I might try the "Rescue Bit" designed for drilling out hardened steel such as drill bits, taps and Easyouts.

3. Seems like heat and penetrating oil is a good idea when I get to the stage of making the screw move with the Easyout.

4. The engine is mounted on the plane as I have been working on cowl and baffles. That makes getting the head into a vertical position quite difficult but not impossible. I am fascinated with the idea of the Nitric acid. If it comes to that, the best way of doing it would be to pull that cylinder, leaving the rest of the engine in place.

5. I am not certain what benefit swapping cylinders would be, unless replacing #3 entirely with a new one is what is being suggested. I had already decided to do the washer mod or something similar

6. There is nothing of the screw protruding. In fact it is below the surface of the hole. So I can't tig weld a new head onto it. Great idea though if there was just a little of the screw protruding.

7. How it happened? I had drilled a short hole (no more than 1/16) in the broken screw using my best small bit, which is a Dremel 2mm. I switched to a new 'jobber' #40 to continue. It is slightly bigger at about 2.4mm I was using low speed and high pressure, which I thought was the correct procedure for hard metals. The bit immediately gripped on the hole and snapped off low down. Somebody commiserated with me for breaking off the screw. That was the previous owner, not me. I just made it worse.

8. Drilling a new hole lower down is obviously a last resort and I would pull the cylinder and give it to a professional if that was the only remaining option.

Finally, I promise to report back once I have it solved, which could be soon but could also take a long time
Click to expand...
I have removed lots of these, even smaller ones that where broken off even and lower then the surface with a TIG welder, you just build it up tell you can weld a nut on or just grab it with vice grips. If only you where closer I would fix you right up.
 
TIG or MIG

I have used both on several broken off bolts. Some as much as an inch below with a stick welder. The flux will protect the the threads. About the easiest in my book if you broke a carbide off in it!
 
Tbone said:
I have used both on several broken off bolts. Some as much as an inch below with a stick welder. The flux will protect the the threads. About the easiest in my book if you broke a carbide off in it!
Click to expand...
Ya welding is definitely the way to go, never had much luck with other methods but it?s not in everyone?s skill set.
 
I can't weld

Welding is not, as Russ says, within my skill set. Mine was an academic education, unfortunately.

I clearly don't understand enough about MIG/TIG welding if, as Terry says, the flux will protect the threads. However, I bet I can get hold of someone (and their machine) who does understand.

On the other hand, the worst that can happen by trying a burr is that it won't 'cut it' in any sense of those words. So I am still going to try that first because I don't see that it can make things much worse and at least the process is entirely within my own control.
 
I hate when that happens.

Wow, I hate when that happens. One time I broke a drill bit off the same way in another type of situation. A friend of mine lent me some left handed drill bits (that's a drill bit that's drills in, going in reverse in case you didn't know) and it grabbed the broken bit and spun the bit and screw out. Maybe I just got lucky but it might be worth a try. I think he got them a Sears.
 
Many times that screw is broken off because the hole is a 10-24 hole and someone screws a 10-32 screw into it and makes a mess of the threads and then the 10-32 screw picks up and when you try to remove it, the screw head breaks off because the steel screw has become one with the alum head.
A last ditch effort is to heat up what is left of the screw until molten with a oxy-acetylene torch, set with a very pin point inner flame, and once the screw is molten, blow the molten steel out of the hole. The aluminum dissipates the heat way faster then the steel so the steel melts before the aluminum and the cylinder shouldn't be damaged, if done carefully.
Also if you fail at all attempts. Don't replace the cylinder, just trade places with another one that still has a functional hole. Move the cylinder , piston and rings as one, and just replace seals and gaskets. you will be OK and spend considerably less than a replacement cylinder.
Good Luck,
Mahlon
 
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mahlon_r said:
Also if you fail at all attempts. Don't replace the cylinder, just trade places with another one that still has a functional hole. Move the cylinder , piston and rings as one, and just replace seals and gaskets. you will be OK and spend considerably less than a replacement cylinder.
Good Luck,
Mahlon
Click to expand...

Now that is a true gem of an idea.
 
dental drill

I have had to remove broken bits in similar situations-a dental drill with used 330 bits are the best but 556 or 557 works also-it will grind the drill bit right out-I can loan you a dental handpiece and burs f you cover shipping both ways-but after you use it you will want one-pm if I can help
 
You have to love it when Mahlon still trolls these boards and provides us with his wisdom and knowledge.

Thank You Mahlon.....
 
Loman said:
snip . . <It is slightly bigger at about 2.4mm I was using low speed and high pressure, which I thought was the correct procedure for hard metals. . . . > . . snip
Click to expand...

You are correct, but the screw in the core is just not that hard, and don't use pressure with a pre drilled hole.

Don't forget - heli-coil :D

i am 50:1 against getting the thing to back out, worth a try but don't break off the ez-out.

Yeah, the TIG would save your day if someone there can roll one over to your hangar. Trust the experts that have spoken. I would not even think about engine disassembly for this, you can fix it much easier than that!.
 
Mig welding

I get 99% of broken bolts out by welding a washer on first. AN970 washers works best. Easier to make contact with the broken bolt if it's lower than the surface. The washer can be a size bigger than the bolt. The weld won't stick to the aluminum cylinder. Then tack weld a nut on the washer and turn the bolt out.
 
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