Re-building track idler wheels

[400brian]

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.

[400brian]

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. If the rivets do not drive out easily, center the drill bit on the rivet and drill the shank a bit and try again. If you beat on the aluminum center too hard you will distort it.

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. A short bolt about 3/4" in diameter can be put in the bearing to give a better surface to strike.

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. I find that an assortment of old bearing lock collars of sufficient size come in handy to use in this process as well.

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:

[400brian]

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. You can 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 ) but that is messy and probably overkill.

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.

[400brian]

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"

[400brian]

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?

[400brian]

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

Wahl Racing sells an NTN cold weather bearing. 6205 ( 52mm OD 25mm ID 15mm wide ) $9.95 These are the bearings I recommend nowadays.

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.

[400brian]

Update: In the 8 years since we first started rebuilding idler wheels, we have learned a couple of things.

We have experienced some bearing failures far too early, particularly in the wheels that have the smaller opening in the aluminum center that did not use the separate seals.

Premium bearings are my best recommendation at this point. A couple of possibilities:

Wahl racing sells a NTN bearing they use in their ice racing skids. If these were unacceptable I assume they would hear about it in short order.
I am rebuilding the idlers in my X8 for the first time now, and I am going to test these. Joe Rainville is also planning to test these in his Dator race sled.

Matt Gabler tells me that he has been using a Koyo bearing in the idlers he has been rebuilding for the guys running the 78 CC skids that Brock Weber has been cloning. He tells me it is bearing: 62052RSNRC3. I believe the C3 suffix indicates that this is an electric motor bearing. Dustin Elder reports that they have ran these hard, and have had no failures to date.

Water infiltration is obviously the problem here. High quality seals are what you need.

[400brian]

The bolt I have been using for the last ten years or so to support the rivet heads when setting the shop side, had gotten pounded pretty much flat.
I picked up a hardened tool to fix this. This is a replacement part for a tool called a rivet squeezer. I bought this off ebay for less than $7.
I squared up the end of my bolt, then drilled a 3/16" hole down the center. I had to open up the hole with a 1/4 drill at the very top to accommodate the fillet at the head of the rivet set. A little yamabond on the shank, and after that sets. it should be good to go.

There are different styles of rivets. You need to choose a set that matches what you are using. In my case, I am using aircraft rivets known as universal head AN470. These have a slightly flatter head than a typical dome head, and closely match what was originally used I think.