What Is This Around This Motor?

Wild guess would be mu metal to shield the magnetic field from the inside of the motor to the outside.

RF shield.

I believe chuck wins this bet, I'm pretty sure it's the mu metal shield.  We had similar ones on motors for avionics.

Thanks guys, I'll leave it on.  I've noticed them before but never thought about it until now.

I'm about 1/3 of the way with installing PS2 in the "J".  I ordered the kit Saturday from MB Klein knowing they were closed Monday.  I can't believe they got it here so fast .  It's only a little over a 4 hour drive for UPS but still, that's great service.

I've seen other motors with them, not sure why they deem it necessary.

I had read the motors Williams used in these engines were windshield wiper motors, but I'm doubtful about that.  The motors in the 2-8-2, 4-6-2, and 4-8-4 "J" (all Samhongsa built) are more or less identical to the motor I took out of the Canon printer I had.  All 4 motors have the shield on them.  Good thing is if a motor fails, I have a replacement!

It's an RF shield. Those motors are used primarily in printers where RF interference is an issue, not magnetism.

Here is an example: RS-555PH

You guys are splitting hairs. RF and magnetism go hand in hand.

Here's a sheet on your example:  Mabuchi DC Motor RS-555PH, they seem to think it's a magnetic shield, and that's sure what it looks like to me. Note the statement: "Has "wrap around" magnetic shield.

An good RF shield is simply a totally enclosed case.  If RF shielding was important on these motors, there would not be holes near the brushes to allow RF emissions to escape.

Flash, RF interference and magnetic fields, while distant cousins, are not even close to the same thing, and also would be handled totally differently as far as shielding.

So John, does that mean the shield is non-magnetic, meaning that it's there to PREVENT stuff from sticking to the motor housing?  That would make sense, but I haven't tried it yet to find out.

It's there to shield the magnetism coming and going, we used to use mu metal shielding on sensors for engine instrumentation on jet and turboprop engines.  I have a bunch of Lionel motors with the same shield, but I'm not sure why the deemed it necessary.

Once we had some 60 Hz interference in a Chem lab and put the electronics in an aluminum box...which did nothing. Then we tried a soft iron box and the interference was gone. So there you have it...a magnetic field from the 60 Hz in the lab.

BTW I think most mu metal does shield rf up to maybe 100 KHz. But higher freqs need a Faraday shield.

I was thinking that the holes in the motor would be on the order of 25 GHz in wave length...so the metal case of the motor probably is a good enough, if also needed, RF shield on it's own.