View Full Version : bonding magnets to drain plugs

Herb W
09-23-2003, 08:17 PM
I have some nickel plated rare earth magnets from Lee Valley which I want to glue on to steel drain plugs (for gearboxes).

Don't suppose they'd move anyway but I believe it's standard practice to have them attached.

What's the best product to use for this job?

John Garner
09-23-2003, 10:43 PM
Herb --

I'd be inclined to bore a recess into the drain plug and glue the magnet into the recess. Just about any oilproof adhesive should work, but I'd lean toward an epoxy such as J B Weld.


09-23-2003, 11:17 PM
JB weld, supermend, or a flexible epoxy, maybe loctite has a product. I wouldn't use any of the standard epoxies, they're just not that good and won't hang on with the temperature changes. The recess is a really good idea, but don't make it a press fit, let the epoxy fill the gap. Coat the magnet also.

09-24-2003, 12:06 AM
Use this stuff that I found when looking for something for Thrud. Oil makes it stronger.

The description:

LOCTITE® Hysol® Product E-214HP is a light paste, industrial grade epoxy adhesive. This one-component, no-mix, heat activated formulation develops tough, strong, structural bonds which provide excellent peel resistance and impact strength. When fully cured, the product offers superior thermal shock resistance, excellent mechanical and electrical resistant
properties, and withstands exposure to a wide variety of solvents and chemicals.

Bonds to a wide variety of materials, including metals, glass,
ceramics and plastics.

Try this link: http://www2.loctite.com/int_henkel/loctite_us/index.cfm?layout=6&productline=E214HP&disp_language=en

Michael Az
09-24-2003, 02:42 AM
Herb, I bought some of those magnets and they work great. I thought about doing the same thing, but the plating is pealing off the magnets and I don't want that in my oil. Don't know if they all do that or not. You could cover the magnet with jb weld to prevent the plating from coming loose.

09-24-2003, 03:04 AM
They don't do that unless broken or defective. Contact Lee Valley and they will replace them.

If you machine a recess for the magnet as JG suggests you will not need the adhesive. You will also never get the magnet out again and its attractive force will be multiplied quite a bit. The steel cups LVT sells for these have a slot milled in them to use a small prybar...I mean screwdriver to "pop" them out. Yeah, you can pop them out, if you can get a pryb...screwdriver under the magnet!

If you add a small amount or RTV or Permatex #2 on the back of the magnet and then set it in the recess it will never come out. Set it even or slightly below the surface of the plug to prevent damage to the magnet if it grabs on to some steel accidentaly.

We used to glue Magnetron magnets in rear end covers and tranny pans - it is a bitch to clean off the filings off of them.

[This message has been edited by Thrud (edited 09-24-2003).]

09-24-2003, 11:08 AM
Like Thrud, I have used magnetron magnet CHIPS (which don't hold as well as the unbroken stuff), in oil pans, transmissions, lawn mowers etc. They really don't shift. I doubt I would epoxy them in place- epoxy surely would not hurt, but I don't think those Lee valley magnets will shift.

BTW: Hard drives have some good magnets in them. Small capacity hard drives are worth pennies in flea markets around here- they may not be working, seller may think he has fooled his customer, but if the case is good there should be good magnets in there.

I needed a timing mark (old mark needed mirror and eyeball on a stalk like a crabs to see. I put one of the Lee Valley magnets on the engine- not a real flat surface either- and forgot to take it off. The corner I used for marking still agrees with the manufacturer's mark after years and thousands of miles. I would not even epoxy, and I just try to slide the magnet through the drain hole and let it lay on a magnetic surface. The number of "whiskers" on the magnet are scary,

Edit comments: 1>I failed to consider the nickel plating peeling- Maybe the old alnico chips would be better than those Lee Valley magnets.
2. THose lee valley magnets are so strong that that if the crank shaft is on the down stroke and near the magnet, your starter won't break the shaft loose. and you will lose 10 HP, the induced currents in the crank shaft journal will weld the bearings. http://bbs.homeshopmachinist.net//wink.gif

GO on gents- First liar ain't got a chance!!! http://bbs.homeshopmachinist.net//smile.gif

[This message has been edited by docsteve66 (edited 09-24-2003).]

Herb W
09-24-2003, 02:41 PM
Quite so doc...the largest size of these magnets (1"dia) must be used with great care.
Been known to suck C clips from axle shafts.

Also been reported that owners of precision lathes like say a Monarch 10ee or a Hardinge have to be very careful... one of these stuck anywhere on the machine can cause enough distortion to affect the accuracy of the work by .0000002 maybe even .0000003". That kind of gross error drives those poor guys right wild...

09-24-2003, 03:04 PM
These magnets may be found on the laser head in a CD-Rom drive. They are tiny, some as small as .01 square. Handling these require great care as they are incredibly powerfull. I took apart such a drive once and dropped one of the magnets on the floor. Luckily, there are always two. To find the dropped one I waved the other about 3 feet above the floor. I suddenly felt excruciating pain in the finger holding the one I was waving. Imbedded in my finger was the lost magnet. I tried to pull the other magnet off my finger but that only succeeded in pulling the one that punctured my finger deeper. I finally hit upon the answer. Using a soldering iron and ignoring the terrible pain I heated one of the magnets above the Curie Point so it lost it's magnetism. I was then able, through a red haze, to pull the imbedded magnet out of my flesh. BE CAREFUL!!

[This message has been edited by Evan (edited 09-24-2003).]

09-24-2003, 03:48 PM
Holy cow! I can see these hip boots aren't high enough. 'scuse me while I go find my chest waders. http://bbs.homeshopmachinist.net//biggrin.gif

09-24-2003, 04:05 PM

[This message has been edited by pgmrdan (edited 03-08-2004).]

09-25-2003, 06:49 AM
You really do have to be careful with those new magnets. If you are carrying more than a few at a time, you have to walk east to go north, and west to go south. Be very careful when getting in and out of a vehicle, and never go into a metal building alone.

09-25-2003, 12:40 PM
Uh. What about attaching it to the outside of the drain plug?

09-25-2003, 12:58 PM

Unfortunately, that won't work. Steel has fairly high magnetic permeability, meaning that it basically short circuits the magnetic field. The field mostly can't penetrate the steel. It would be possible to magnetize the drain plug but steel doesn't make a very strong magnet.

09-25-2003, 06:00 PM
I was worried about the magnet coming away and going into the works of the engine, but in hindsight, they stick so well that unless another piece of metal comes in contact over a significant area of the magnet, it isn't going to go flying off anywhere. I'd still want to coat it over with whatever you use to hold it in place, as a wear resistant coating (you'll be wiping metal bits off of it when cleaning it), and to keep it's own coating intact.

09-25-2003, 08:41 PM
We talked about these rare earth magnets in reference to musical instrument repair a while back. Someone pointed out that the attraction of the magnet was either an inverse square law or something even more drastic. The attraction force is decreased by the square of the distance to the object being attracted. In other words the further away you get the object from the magnet, the less attraction there is, and it isn't in a linear form.

I have two 1 1/2" x 5/8 " thick rare earth magnets, and if I stick them together I have to slide them apart and pull as hard as I can to remove them. I ain't as strong as Thrud, but I ain't no weakling either. I also have a 1 1/2" x 1" magnet I've used for instrument repairs. Its a monster, and fun to work with but be careful.

I don't think I would use anything but the magnet in the pan assuming the pan is steel and the magnet is stuck firmly to it.


09-25-2003, 08:48 PM

It's inverse cube law. It really drops of with distance in a hurry.

[This message has been edited by Evan (edited 09-25-2003).]

09-25-2003, 11:50 PM
I have about a 1' "stick" of magnets taken from hard drives. They will move theirselves to a peice of steel 6" away. One on either side of hand will stick to themselves.

09-25-2003, 11:55 PM
I wasn't entirely jesting about the magnets in CD-Rom drive laser heads. They do exist and some are so strong that when they stick together I have to slice them apart with a knife blade.

09-26-2003, 12:43 AM

I may be strong, but I can't fart at will - so my super power is pretty lame... http://bbs.homeshopmachinist.net//biggrin.gif

I know of a supplier that has rare earth magnets with a 2,000Lb. pull. They use these in housings to make PM sheet lifts that will pick up 10,000Lbs. - works like a magnetic indicator stand on a more powerful basis. It costs a fortune to ship them by truck because of their extreme danger in handling.


People have been straping magnetron magnets to their oil filters for years around here. The steel still allows magnetic attraction of filings and turnings in the filter. I have used a pipe cutter on many oil filters to see if it was any useful effect - it does. A magnetic plug is far better, however.

I have a friend with a suburban that he put magnets on the fuel, air, and heater lines and it does have a benficial effect. We have proven that they work (to ourselves) on a chassis dyno (Loveseths). As a student of physics, I can't explain it - but I am still trying to figure it out. I don't buy the claims of the people that sell these in the least. Thought you might find that interesting.

[This message has been edited by Thrud (edited 09-25-2003).]

09-26-2003, 01:33 AM

I did say "mostly". Steel is not 100% permeable to a magnetic field. For that you need mu metal, used to be used to shield oscilliscope tubes (Now we have LCDs). As for the benefit of "magnetizing" the fuel etc. Hmmm... ???

Herb W
09-26-2003, 01:58 PM
Thanks guys, for the advice and the humour.

I think that John's suggestion - boring a recess, is a good idea, and that when done this way, bonding probably isn't necessary.

The nickle plating shouldn't flake off (I hope)...I'll check it whenever I have 'em out.

The guys at Acklands-Grainger gave me a loctite catalogue a while back...didn't realize that they had such wide variety of products. Frustrating 'home shop' problem though - be nice to have some of those specialised adhesives on hand but they'd probably 'expire' & be useless before I got around to using them.

I'm impressed with these little magnets. I was playing wi...uh, I mean conducting experiments with one - .5"dia x .125 thick.
Stuck it on a drain plug & found that it's lifting limit was around 6lb.- just lifted a 6lb sledge (not kidding...this time).

09-26-2003, 03:34 PM

[This message has been edited by pgmrdan (edited 03-08-2004).]

09-26-2003, 05:18 PM

Magenetism is the exception. For light and gravity it is inverse square. For magnetism it is inverse cube law.


09-26-2003, 05:30 PM

[This message has been edited by pgmrdan (edited 03-08-2004).]