Re-building track idler wheels

by **400brian** » Fri Dec 26, 2008 2:13 am

The question has come up: What do I do for idler wheels? The idler wheels used on the slide rail sleds seem to have become generally unavailable. Apparently these were a popular replacement item, the NOS supply has been burned through, and Kimpex seems to have discontinued the aftermarket ones.

First off, DON"T THROW ANY AWAY! Save them for parts, we're going to need them.

This is a description for rebuilding the original aluminum centered idler wheels.

What has to be done, is the wheels have to be disassembled, the bearings removed and replaced, and the wheels re-assembled.

1) To disassemble: you must first remove the rivets holding the centers together.

Center punch the factory side of the rivet head ( dome shaped side ), then drill with a 3/16" or slightly smaller drill bit, JUST THE DEPTH OF THE HEAD!
Then take a pin punch that fits that hole nicely, and pop the head off with a rocking motion.

Attachments:

by **400brian** » Fri Dec 26, 2008 2:30 am

You may have to use a small chisel to finish removing the head. OK, once you have the head of the rivet popped off, take the pin punch and drive the headless rivet out of the wheel center. Repeat for all the rest of the rivets.

To separate the wheel center halves: Hold the wheel in the palm of your hand, and rap the center of the bearing with a hammer. A couple of raps, and it should pop apart. Then flip it over, and pop the bearing out of the remaining half.

These are metric bearings, ( 52mm OD, a 25mm ID, and 15mm wide ) mounted on a fractional shaft, so there are reducer bushings in the bearing to bring it down to size. These must be removed and re-used.

To remove the reducer bushings: set the bearing in the open jaws of your vise, and with a punch with at least 1/4" tip ( a nice square tip ) tap the bottom bushing out. There is a small gap between the two halves, and that is all you've got to work with.
Get the tip of the punch in there, and give it a sharp rap on opposing sides.
Once the bottom one is out, flip the bearing over, and with a large bolt or piece of shaft, you can tap out the remaining half without damage.
Clean up any dings or burrs you have put in the bushings removing them, as they need to slide on the shaft later.

Here's a look at the parts:

Attachments:

by **400brian** » Fri Dec 26, 2008 2:54 am

I've found there to be at least two different styles of idlers. The difference between them is the size of the center opening, and the type of seal used on the bearing.
In either case, the bearings are not sealed, I would call them shielded.
On the centers with the larger opening I re-used the original shields/seals with my new sealed bearings. Mostly for looks, I put a little moly grease on the underside, and put them on the new bearing after I had tapped in the reducer bushings.

On the centers with the small opening, the metal part of the shield/seal is of a different design, and cannot be used with the new sealed bearing. However, I did put the red rubber seal on the new bearing, again mostly for looks.

Clean everything up, there is always some corrosion inside the wheel center. Apparently the rivet holes were punched, this caused metal to smear between the two halves, use a file to smooth this up.

To re-assemble:

Install the reducer bushings in the bearing. Install the shields/seal if you want. I put a bit of gasket sealer where the bearing goes into the center, and on the rim of the rubber tire ( to help keep moisture out ). You have to support the wheel center with something, as the bearing sticks out of the center when in place. I used a collar that was larger the the bearing well area of the center. Then tap the bearing into a center ( I used an old bearing race ). Then put the other center on ( line up the rivet holes with bolts or clecos ) and tap that down into place. The centers will touch when complete. There are three sets of three holes, turn the center till you find the position that lines up the best.

This photo is of the wheel with the large center opening, original shield/seal installed, and two rivets have already been driven.

Attachments:

idler_wheels_001.jpg (179.07 KB)

by **400brian** » Fri Dec 26, 2008 3:14 am

Solid rivets should be used to re-assemble the wheels. They are 3/16" in diameter, and the length required are 3/8" at a minimum, but preferably 1/2".
Rivets can be obtained from McMaster Carr, or any Aircraft Suppy Co., like Wicks.

The 3/8" rivets make a shop head slightly smaller than I liked. The 1/2" long rivets give a nice robust shop head, but are harder to drive straight. The first hit is the most important, get it straight and square, and you get a good result, bend the rivet with the first blow and it's harder to get a good result.

To drive solid rivets, you have to support the factory head. Rivet sets are made, but I couldn't find what I wanted. The best way to drive a solid rivet would be with a riveting gun and a bucking bar. A concave set goes in the gun ( air hammer with sensitive trigger ) and it is used on the factory head, while the bucking bar ( heavy chunk of steel of various sizes and shapes ) is held to the side soon to have a shop head.

I don't have any of that, so I had to improvise. I used a 7/16" bolt of several inches in length ( which had a concave end ) held in the vise, which I placed the factory head in while I drove the rivet with a chunk of steel. Use a short piece of shaft, something you can handle easily, and big enough in diameter that you don't slide off the rivet.

You are trying to drive the rivet straight down, and you can stop when you achieve a shop head diameter of one and a half diameters of the rivet
3/16 = 6/32 so a diameter and a half would be 9/32"

Attachments:

idler_wheel_rebuild_005.jpg (187.54 KB)

by **400brian** » Fri Dec 26, 2008 3:22 am

Put clecos or bolts in at least half if not all of the rivet holes before you begin riveting. Bolts will give you the best clamping force.

Make sure the shop head stays in whatever you are supporting it with, or you'll get a smiley in it. Put something on the anvil side of the vise to hold the wheel in a level position. It takes 6 or so raps to set the rivet.

Any questions?

Attachments:

by **400brian** » Thu Mar 11, 2010 3:38 pm

Mc Master Carr stocks both the bearings and rivets.

Bearing part number: 5972K46 $8.73

Rivet part number: 97490A245 sold in packs of 100, $5.36

After trying both, I think the rivets I got from Wicks Aircraft Supply drove easier. Aluminum hardens as it ages, so this may mean that the Wicks rivets are fresher.