Stuck screws on bendix mag

C

C_Parker

Pre-takeoff checklist
Joined
Mar 11, 2019
Messages
150
Display Name
Display name:
x
Anyone have any pointers on getting seamingly stuck cover screws off of a bendix mag (on an o-470)? One of my mags couldn't be opened for inspection. My mechanic says I need to spend $1k on a new mag...
 
Try an old fashioned large soldering iron, melt a small blob of solder on it, and apply to the screw head for 30 seconds to heat expand the screw, immediately apply the RIGHT size screw driver. Repeat if necessary, a little longer each time. The large soldering iron is essential, as it is a strong heat sink, and will not cool in contact with the screw. Electricians, plumbers, and copper smiths use them.

The screw expands faster than the surrounding metal, and length is the issue, not diameter. If there is thread lock, heat will release it too. Obviously, do one at a time, so the heat is very local.
 
C_Parker said:
Anyone have any pointers
Click to expand...
Is the mag off the engine? If not remove and put in vice. In past have had to drill stripped screw heads (phillips/allen) off and replace screws.
 
  • Like
Reactions: JPA
Anyone who has worked on vintage motorcycles has probably had to remove some stuck screws. First thing I’d do is put it in a vise And if the heads aren’t too screwed up yet I’d try an impact driver or a screwdriver and a hammer. If they’re too mangled you could try slotting the screw head with a dremel too. Worst case you drill the head off and get it apart, then the shaft of the screw usually releases and can be turned out by hand.

Unless this airplane lives in a horrid environment or the magneto has been sitting in a pool of salt water I have never seen a magneto with any corrosion on it or screws so crusty they wouldn’t come apart.
 
Thanks guys, the weird thing is this plane has lived most of its life in Arizona and Idaho!
 
geezer said:
Try an old fashioned large soldering iron, melt a small blob of solder on it, and apply to the screw head for 30 seconds to heat expand the screw, immediately apply the RIGHT size screw driver. Repeat if necessary, a little longer each time. The large soldering iron is essential, as it is a strong heat sink, and will not cool in contact with the screw. Electricians, plumbers, and copper smiths use them.

The screw expands faster than the surrounding metal, and length is the issue, not diameter. If there is thread lock, heat will release it too. Obviously, do one at a time, so the heat is very local.
Click to expand...

Screw is steel, surrounding metal is aluminum so the screw would expand less, not more or "faster" if both are close to being equally heated. Screw expanding less could loosen it, I guess. If the screw expanded more or "faster" then how would that loosen rather than tighten the screw? Also how is length, not diameter, the issue here?
 
Fine valve grinding compound on the tip of a new driver or tip. Heat gun to warm the aluminum around each screw. Must be square to the screw. Could be done on the engine, but better if removed and held fast in a vice.
 
I can't imagine spending $1k on a new mag just because a screw is being difficult. Sounds like your A&P is just looking for the easy way out. Lots of good ideas on here on how to get the screw out.
 
Have you tried PB Blaster? I have had good luck using it to help loosen corrosion or rust that is holding screws or bolts in place. You can find it in the Aviation Department of your local Home Depot.
 
Aerokroil is my go-to concoction for freeing stuck fasteners. I was introduced to it by a mechanic for Shell Aviation. I was installing a new rooftop package unit on their hangar, and couldn't get some of the fasteners loosened on the unit being replaced.

Shell was one of the first corporate flight departments to receive a GIII, and the staff allowed me to check out the cockpit and interior (after I donned booties). The aircraft was on the cutting edge, and this spam can driver was mightily impressed.
 
Shootout between 7 different penetrating oils.

Punchline: Liquid Wrench won.
 
You can try a speed handle with a fresh and proper phillips bit. Secure mag in a vice, put some good downward pressure(may need to support from below with wood) and give it a good swift torque breaking snap to the left. That’s how we would remove frozen screws to not have to drill out. Never busted a head off, worked every time.
 
Domenick said:
Shootout between 7 different penetrating oils.

Punchline: Liquid Wrench won.
Click to expand...
Color me shocked. I'd grown up w/ Liquid Wrench back in the 60s and 70s. When some of my mechanic friends introduced me to PBBlaster a decade or so ago, I was amazed by how much better it worked. Hmmm... who knows. Maybe I'd just gotten more patient by then and let it soak longer, or my tools themselves were better.. or all of the above.
 
MuseChaser said:
Color me shocked. I'd grown up w/ Liquid Wrench back in the 60s and 70s. When some of my mechanic friends introduced me to PBBlaster a decade or so ago, I was amazed by how much better it worked. Hmmm... who knows. Maybe I'd just gotten more patient by then and let it soak longer, or my tools themselves were better.. or all of the above.
Click to expand...

Same experience here. Liquid Wrench was a staple in my Dad's garage, and I used it for years as an adult. Once I was introduced to PB, however, I haven't looked back. PB has never let me down.
 
Domenick said:
Shootout between 7 different penetrating oils.

Punchline: Liquid Wrench won.
Click to expand...

Meh, according to his test Aerokroil is only marginally better than nothing at all. Kinda voids the test results for me since my experience is quite the contrary. But hey, I am happy to see folks make efforts like this and hope he get lots of views (1k views = $1 revenue approx.) You just have to take all these amateur efforts with a boatload of salt.
 
What I've found most effective is the "woodpecker" or similar device:

https://aircraft-tool.com/shop/detail.aspx?id=AT540A-KIT

The air hammer or rivet gun vibrates and loosens the screw while torque is being applied with the wrench.

I've never seen a stuck screw made loose with penetrating oil. However, if the screw is made to move just a little, the application of penetrating oil will usually loosen it up considerably and prevent it from re-sticking and shearing.
 
flyingbrit said:
What I've found most effective is the "woodpecker" or similar device:

https://aircraft-tool.com/shop/detail.aspx?id=AT540A-KIT

The air hammer or rivet gun vibrates and loosens the screw while torque is being applied with the wrench.

I've never seen a stuck screw made loose with penetrating oil. However, if the screw is made to move just a little, the application of penetrating oil will usually loosen it up considerably and prevent it from re-sticking and shearing.
Click to expand...

Yes, those are good and I keep meaning to add one to my toolbox. I also like what I call my "miracle screwdriver", a Vessel Impacta #2 JIS (NOT Phillips). Not only does it grab a Phillips head screw much better than a standard Phillips screwdriver, you also have the option to use it as an impact driver to loosen (only if the backing surface is sturdy enough to take a blow, not for sheetmetal). Combined with Aerokroil, I have definitely impressed other A&P's.

https://www.amazon.com/Vessel-Megadora-Impacta-P2x150-Screwdriver/dp/B003BGZ9CO/
 
flyingbrit said:
...

I've never seen a stuck screw made loose with penetrating oil. However, if the screw is made to move just a little, the application of penetrating oil will usually loosen it up considerably and prevent it from re-sticking and shearing.
Click to expand...

Regarding this, my experience is that if I start putting torque on a fastener and it does not start moving when I think it should plus a bit then I put Aerokroil on it, wait, and try again. Rinse and repeat. Often that does the trick.
 
alfadog said:
Yes, those are good and I keep meaning to add one to my toolbox. I also like what I call my "miracle screwdriver", a Vessel Impacta #2 JIS (NOT Phillips). Not only does it grab a Phillips head screw much better than a standard Phillips screwdriver, you also have the option to use it as an impact driver to loosen (only if the backing surface is sturdy enough to take a blow, not for sheetmetal). Combined with Aerokroil, I have definitely impressed other A&P's.

https://www.amazon.com/Vessel-Megadora-Impacta-P2x150-Screwdriver/dp/B003BGZ9CO/
Click to expand...

Nice!! Just ordered...thanks.
 
There are numerous reasons a screw might be stuck. It might have been overtorqued. It might have been installed with a high-strength threadlocker like Loctite 262, which should never be used on small fasteners. It might be held there by corrosion. Heating the screw can help release Loctited screws but you need some temperature, since it can hold tight up to around 350°F. Corrosion is often softened by heat as well. Overtorquing often stretches the screw and wrecks the threads on both the screw and in the hole.

I wouldn't use any impact devices on it. Those rattler screw-removers can loosen internal components and Brinell the bearings.

I would drill the heads off and get the cap off and grab the stub with vise-grips and start wiggling it left/right. A bit of penetrating oil will help if it's corroded in there. Patience and a lot of gentle left-right twisting usually pays off. Last resort would be to carefully weld a chunk of scrap steel rod to the stub, and after a couple of left-right attempts it will probably come right out. A mig welder is best for this since it's quick and focused. Too much heat will melt the aluminum casting and wreck it.

In the 80's, in the air-brake component remanufacturing business, I removed many thousands of stuck fasteners from aluminum, steel, cast iron and even zinc/aluminum alloys (mostly zinc in the mix), which has phenomenally low melting point. Taught the techniques to the employees, and we usually saved expensive core parts.
 
flyingbrit said:
What I've found most effective is the "woodpecker" or similar device:
https://aircraft-tool.com/shop/detail.aspx?id=AT540A-KIT
The air hammer or rivet gun vibrates and loosens the screw while torque is being applied with the wrench.
Click to expand...
Mechanically, how does it work? I see no way yo make it "vibrate."

alfadog said:
Yes, those are good and I keep meaning to add one to my toolbox. I also like what I call my "miracle screwdriver", a Vessel Impacta #2 JIS (NOT Phillips). Not only does it grab a Phillips head screw much better than a standard Phillips screwdriver, you also have the option to use it as an impact driver to loosen (only if the backing surface is sturdy enough to take a blow, not for sheetmetal). Combined with Aerokroil, I have definitely impressed other A&P's.
https://www.amazon.com/Vessel-Megadora-Impacta-P2x150-Screwdriver/dp/B003BGZ9CO/
Click to expand...
Is the bit replaceable?
 
Domenick said:
Mechanically, how does it work? I see no way yo make it "vibrate."


Is the bit replaceable?
Click to expand...
The skinny end goes into your rivet gun. It gets hammered hard by the gun. The bits are replaceable.

15601_3_.jpg
 
  • Like
Reactions: JPA
Dan Thomas said:
There are numerous reasons a screw might be stuck. It might have been overtorqued. It might have been installed with a high-strength threadlocker like Loctite 262, which should never be used on small fasteners. It might be held there by corrosion. Heating the screw can help release Loctited screws but you need some temperature, since it can hold tight up to around 350°F. Corrosion is often softened by heat as well. Overtorquing often stretches the screw and wrecks the threads on both the screw and in the hole.

I wouldn't use any impact devices on it. Those rattler screw-removers can loosen internal components and Brinell the bearings.

I would drill the heads off and get the cap off and grab the stub with vise-grips and start wiggling it left/right. A bit of penetrating oil will help if it's corroded in there. Patience and a lot of gentle left-right twisting usually pays off. Last resort would be to carefully weld a chunk of scrap steel rod to the stub, and after a couple of left-right attempts it will probably come right out. A mig welder is best for this since it's quick and focused. Too much heat will melt the aluminum casting and wreck it.

In the 80's, in the air-brake component remanufacturing business, I removed many thousands of stuck fasteners from aluminum, steel, cast iron and even zinc/aluminum alloys (mostly zinc in the mix), which has phenomenally low melting point. Taught the techniques to the employees, and we usually saved expensive core parts.
Click to expand...

Those are all excellent techniques. My go-to's are:

  • JIS on Phillips just for its superior grip.
  • Aerokroil.
  • My new fav, Vampliers. Or Vise-grips, or channel locks.
  • Tapping CCW on the circumference with a small sharp chisel.
  • Grind a slot for a screwdriver or file flats for a wrench.
  • Last resort - drilling the head, screw-extractor as needed (ugh).

I usually don't use heat often and am not a welder.
 
In my experience, Aerokroil is the best penetrant. Liquid Wrench is below WD-40 on my scale, and both are near the bottom.

Someone will soon post an acetone and ATF mix is exponentially better than all of the commercial products.

Of course it's all a matter of opinion.
 
I dunno about that acetone thing on a painted surface tho.
 
We call it a "Grampa" (dunno why)
Dan Thomas said:
15601_3_.jpg
Click to expand...

Might be overkill on a mag though.

Use a left-handed twist drill to drill out the screw. I use this method OFTEN on older planes, or planes that are worked hard (like commuters). The drill eventually catches on the inside of the screw and since it's left-handed, it spins the offending fastener out of the hole. If it does not catch, you have a nice hole for your screw extractor (NOT and EZ-OUT, a real screw extractor)
 
JPA said:
... If it does not catch, you have a nice hole for your screw extractor (NOT and EZ-OUT, a real screw extractor)
Click to expand...
If all else fails, then yes, left-twist bit followed by a screw extractor. Be warned, though... the smaller screw extractors and left-twist bits, even the best ones, can break, too... and they are a REAL mother to get out. They have to be harder than the material they're meant to drill or extract.... and they ARE.
 
Last edited:
Screw extractors aren't going to be much good on these screws. They're a small screw with a socket head, meaning that there is very little metal to grab with an extractor. A left-handed bit the size of the screw head might grab the head and get it loose. Once the head's off you're done with any extractors.
 
Dan Thomas said:
Screw extractors aren't going to be much good on these screws. They're a small screw with a socket head, meaning that there is very little metal to grab with an extractor. A left-handed bit the size of the screw head might grab the head and get it loose. Once the head's off you're done with any extractors.
Click to expand...

Yes, not a big fan of EZ out. And there's no real difference I see between the EZ out and the so-called "real screw extractor" posted above. They're both going to break off if you exert too much torque and then you're screwed. Hahaha. Then you're going to need to drill out and retap and if you've got a broken tool in there you're triply screwed. BTDT. To be honest, what I do with EZ outs is go pretty gentle with them and if they don't come it's drill and retap.
 
alfadog said:
Yes, not a big fan of EZ out. And there's no real difference I see between the EZ out and the so-called "real screw extractor" posted above. They're both going to break off if you exert too much torque and then you're screwed. Hahaha. Then you're going to need to drill out and retap and if you've got a broken tool in there you're triply screwed. BTDT. To be honest, what I do with EZ outs is go pretty gentle with them and if they don't come it's drill and retap.
Click to expand...

Just curious if there's anyone out there who HASN'T learned this the hard way?
 
  • Like
Reactions: JPA
To me, the expectation of a screw extractor removing a bolt/screw whose head broke off due to the threads being corroded is the height of wishful thinking. If the head cannot apply enough torque to loosen the corroded threads there is NO WAY the screw extractor will. The only time I've seen an extractor work is when the bolt head and part of the shank break off due to either shear or tension overloading, and there is no thread corrosion so the low torque of the extractor is sufficient. This is evidence of a poor design or perhaps an accident and is relatively unusual.
 
flyingbrit said:
To me, the expectation of a screw extractor removing a bolt/screw whose head broke off due to the threads being corroded is the height of wishful thinking. If the head cannot apply enough torque to loosen the corroded threads there is NO WAY the screw extractor will. The only time I've seen an extractor work is when the bolt head and part of the shank break off due to either shear or tension overloading, and there is no thread corrosion so the low torque of the extractor is sufficient. This is evidence of a poor design or perhaps an accident and is relatively unusual.
Click to expand...

I got one of the cylinder studs out of an IO-540 last year using an EZ out. And it was tight. I used some heat after doing what I could to protect the case and keeping the heat very local. The fact that it's a beefy stud and I could use a large EZ out definitely contributed to the success. So it does work on large stuff.
 
I'm out on a long cross country flight this week, I'll be digging into this early next week.

Thanks everyone for the input! One way or another, I don't want to buy a new mag unless the mag itself is shot!
 
Last edited:
You must log in or register to reply here.
Back
Top