Shunted brush diameter question

"Lost in translation"?

There has been some talk of how Chinese production has adopted "close" measurements for otherwise established, common items that have been in place 60-70 years or more.

I learned from experience with HO loco motors that sloppy brushes (meaning visible play from side-to-side) will cause more brush arcing on the commutator because the brush does not seat as firmly and uniformly. Then the commutators get dirty and the motors can get balky. The problem is aggravated if the loco does more forward-and-reverse changes, which cause the brushes to rock back-and-forth more frequently.

I fixed sloppy brush fits on some Athearn HO motors by making a sleeve of aluminum foil to fit around the brush, to eliminate the side play while still allowing the brush to move freely up and down in the bore. The brush holders are not real precise, basically a hollow rivet-type material.

It's tricky to make a brush sleeve; I formed the foil around a drill bit shank of similar size and experimented with how much material to use. Don't know if I would recommend it for larger O-gauge motors. It did make the motors run much more smoothly, with slower slow speeds possible.

So my point is, you are right to be concerned by a loose brush fit. It will not give the best motor performance.

Sent email to Lionel last evening and got answer first thing this morning. Nice quick response.  I told them about the size difference and here is what they said:  "The part that you ordered is the correct replacement brush for your locomotive. If there are any issues regarding operation, please let us know."

Somehow, Ace, I believe what you predicted will happen if I install them.  Man, I do wish we could get manufacturing back to this country.

Thanks, guys.

I suspect the looser fit for the brushes is a trade-off to accommodate possible manufacturing irregularities in the dimensions of the bore that the brush fits in. Or it may be an adjustment to metric production. Maybe you could find some old-new stock somewhere else that would fit better?

As a follow-up to Ace's aluminum foil idea-

1. Thin brass foil is readily available as a craft supply, for embossing. Might be better electrically.

2. Seeing as how the brushes are shunted, perhaps a thin coating of epoxy paint, sanded down to a snug fit. Wouldn't work with unshunted brushes, obviously.

The ones Lionel sent should work fine, the shunting wire will prevent most of the arcing.

I put them in and they are working fine thus far.  Thanks.

Chuck Sartor posted:

The ones Lionel sent should work fine, the shunting wire will prevent most of the arcing.

The arcing will be on the brush-commutator interface over time, because a loose fit in the brush-holder doesn't keep the brush aligned as well on the curved surface. May not be an issue with mostly forward-only operation.