proper Rotor Brush length?

[DogBunny]

I know the manual says minimum brush length of 1/4", or something like that, but how does this relate to the mark on the brush? Is the brush good until the mark (see pic) is reached? Or do you add a 1/4" to the mark when you measure?

Bonus question: Does anyone know what the over-all length of a new brush is? I'm asking because I have been making my own brushes, and I'd like to know how long to make them. Maybe someone has a brand-new brush they could measure? Thanks.

 

[jd750ace]

No answer on the original brush length, but that line is the wear limit. If you can't see the line, they are done. Those look to be Yamaha brushes. On aircraft, many times the wear indicator is a diagonal line that starts 20% into the wearable portion. that way, you have an idea of how much brush you have used in your last operating cycle, and approximately how much time you have left. Since running one out can cause some damage to the slip ring, the tech can make an educated decision on whether or not to continue them in service or replace them.

 

[xjwmx]

My manual has both the new length and the minimum length. I seem to remember the new length is the entire length of the graphite. I would ignore the line, myself.

Here's a thread where I make some brushes. It's good to make a little hole in the bracket to put the pigtail through. At this time for some reason I thought my brushes were wearing a lot faster than they acturally were.

http://www.xs650.com/forum/showthread.php?t=4773

 

[TwoManyXS1Bs]

Just read your thread, xjwmx. Those brushes look like Dremel brushes. Got some new ones out in the barn, and will measure later to be sure. Nice tip...

 

[DogBunny]

Thanks to all for the help.
xjwmx, it was your thread that started me making my own brushes some time back. I went to a small motor shop and asked for the closest thing to an old XS650 brush, and I got 4 Bosch brushes that the shop had accidentally ordered for a little over $2 each, and that were just about perfect. But I never knew how long they were supposed to be. Anyways, you shamed me into looking it up in the manual, and I found it in Haynes. The brush length is 14.5 mm, and the wear limit is 7.0 mm (a little over 1/4"). I measured the marks in my pic, and that's where they are, 7.0 mm.

 

[TwoManyXS1Bs]

Well, shure'nuf, Dremel brushes won't work, come close, but way too short. The original Yamaha brushes and MikesXS `70-`79 brushes both measure 5mm x 4.5mm (.195" x .175") in thickness/width. The Mikes brushes don't include the wear indicator...

 

[XSLeo]

I found brushes at Sears Hardware. They have them in a box, which contains them in many sizes. Take an old one with you, find one that is about the right size. If a bit to big, sand them to fit.
The ones I found had a copper circle soldered to the end Just unsolder the circle and solder on the metal mount from an old set.
Leo

 

[xjwmx]

DB, ha!, not to shame you into looking it up yourself. Just that I knew where the info was but didn't need it myself. Might be coming back down there, or SA in some time frame or another. Working hard on a certification that will make me stand out from the crowd down there, hopefully. It's great down there.