Old School Mini Drum Question

[jcorrington]

I got my hands on a 21 mini drum wheel a while back. It didn't have any bearings in it when I got it, so I got some bearings that fit a 3/4" axle and installed them. Then I made some axle spacers, as well as having a machine shop making a special stepped/knurled spacer for the brake face plate side, that creates a little offset to allow the face plate to be stationary while the wheel spins.

So I got this all set up and mocked it up. The problem is that when I tighten the axle nut past about 20 lbs. or so, the bears start to slow/bind. The wheels spins but slowly and not as long. So I think something's wrong.

What I'm wondering is if the wheels is supposed to have a middle spacer/collar inside the hub? In between the bearings to prevent side load? That's the last thing I can think of. I was wondering if maybe someone who has one of these wheels would know the answer.

[JBinNC]

Yes, there absolutely must be a spacer between the inner races of the bearings, on the axle. The spacer must be longer than the distance from bearing to bearing in the hub by ten or fifteen thou. So, when you tighten the axle, the inner races are pulled tight against the spacer, and the outer races float just a little bit in the hub. Any other set-up, and the bearings will bind, as you have experienced, or at least be side loaded enough to increase heat and wear. Good question.

Jim

[jcorrington]

Thank you for the response. So I need to knock out at least one of these bearings. Can I reuse it? I've read that you shouldn't.

Also, any tips for how to determine the spacer length? I suppose knock one bearing out and then poke a stick in there. add 0.015"

[TriNortchopz]

found this;

Front Wheel Sealed Bearing Example

This is not a step-by-step install instruction.
It is rather an explanation of the principles involved in placement of the bearings & spacers plus the overall concept of alignment.

Here is a general diagram of the front wheel in the forks with various parts identified.
This illustration uses sealed-bearings, but the operational concepts apply to use of Timken bearings (with shims) as well.



When installing sealed bearings, install the brake-side first so that the bearing is fully seated in the hub.
This helps to keep the brake rotor alignment in conjunction with the external bearing spacer.
Then place the internal hub spacer into the wheel and install the other bearing.
Be sure that the internal hub bearing spacer is a few thousandth longer than the spacing of the hub bearing seats. This guarantees that the hub spacer will be in full contact with the inner race of the 2nd bearing and the bearing will not be laterally loaded (under tension).
The outer race of the 2nd bearing should NOT fully seat against the hub cavity - You must stop the bearing insertion when the inner race of the 2nd bearing comes in contact with the hub spacer.

Notice in the diagram that there is a small GAP between the outer race of the 2nd bearing and the seat of the hub cavity.
This is important to maintain (as described above) to prevent laterally loading the bearing.

The goal is to never put differential lateral forces on the inner vs outer races while installing the bearing.
We don't want to damage either the balls themselves or their races by causing the inner race to go one way while the outer race is pushed or held the other way.

http://sportsterpedia.com/doku.php/techtalk:evo:wheels01

[jcorrington]

That's a really helpful diagram, thank you.

[TriNortchopz]

Thank you for the response. So I need to knock out at least one of these bearings. Can I reuse it? I've read that you shouldn't.

Also, any tips for how to determine the spacer length? I suppose knock one bearing out and then poke a stick in there. add 0.015"

if you are able to remove the one bearing by having your bearing removal tool only on the outer race, and able to remove it evenly, then it could be re-used... otherwise no, remove and replace.
What is the bearing number? is it a 6204-2RS 3/4 Radial Ball Bearing?

here is a tool to remove bearings which you could make for a couple bucks:



a bolt head is ground down to fit through the bore of the bearing, a saw cut is made about 3/4 of the length, starting at the rounded head, then a chisel or similar tool is used to spread the bolt apart so the underside of the bolt head is against the side of the inner race, then drive it out. the hub can be warmed to expand it for easier removal, or to melt previously used loctite bearing retainer - if it was used.

when the one bearing is out, you can use a depth gauge; a set of dial or digital calipers can do the job nicely

https://www.kmstools.com/neiko-6-quot-fractional-sae-metric-digital-caliper.html

set the end of the caliper shoulder against the bottom face of the bearing bore and extend it to the inner face of the other bearing (make sure the bearing is fully seated in its bore - tap it on the outer race) - ensure the end of the tool is on the bearing race.
This may be helpful:

Proper Use of Digital Calipers
"Use the depth gauge to measure the depth from one surface to the next. Make sure the calipers are perpendicular to the surface being measured. In the animations above, the depth gauge is being used to measure the distance from the surface of an aluminum part to the desk below it. The second animation is incorrect because the calipers are not perpendicular to the surfaces being measured."

https://support.bantamtools.com/hc/en-us/articles/115001656313-Proper-Use-of-Digital-Calipers

check your measurement in a few places, a few times, until you get a consistent measurement, then add your extra 0.010" to get your overall length of inner bearing spacer length.

The bearing spacer will need to be a minimum of 3/4" inside diameter for the axle to fit through;

3/4" ID Wheel Spacer Stock

This product is for those of you who like to make your own wheel spacers but would like to save yourself some time.
This stock comes in 6" sections, the ID is reamed to .752" so it will slip smoothly over your 3/4 axle and has an OD of 1.125".
You just need to lop off the length you need and you have an instant custom wheel spacer.

Made from 4130 chrome moly
Sold in 6" lengths
Sold each $24.50

https://www.bungking.com/3-4-wheel-spacer-stock/

[TriNortchopz]

is this the chop that wheel is going on?

[docmel]

Just me, not a fan of those mini drums. If I have front brake, I want one that works: They do work, but must be adjusted correctly, shoes AND drum must be in spec (dont take short cuts here), just like any other drum type brake, but even then, there isnt much shoe to drum area contact to get alot of stopping power Compare a mini drum to the older front drum on big twins, you get the idea....