WCD Bearing Blocks

I have a question regarding West Coast Drive bearing blocks.

Based on many of the pictures and CAD models I’ve seen, the “standard” way to create them is to cut a pocket all the way thru your 2 x 1 x 1/8 siderail, and then slide a bearing block into the pocket from the side. Once in place, the bearing block gets a plate bolted to it from both sides to hold the block captive in the slot while allowing it to slide front to back.

It seems a simpler approach would be to cut the same pocket in the siderail, but then slide a 1.75 x .75 bearing block in the siderail from the end. This would just fit inside the inside dimensions of the tube, and would eliminate the need for the sideplates and fasteners.

I can see a downside to the simpler approach, and that is that you need access to the end of the tube you’re installing the block in. That doesn’t seem like that big of a deal. I would think the two would be comparable from a weight standpoint. Is there another downside to this approach that I’m missing?

A long, long time ago (before my time even) 973 used to do this.

The problem is the inside of extruded tube is all over the place dimensionally, so this blocks end up being really finicky.

Also, there is some benefit to having the bearings outboard of the 1" tube. Having both bearings only 3/4" apart to the outsides seems a bit narrow.

Bearing blocks are probably the trickiest part to design and machine of a WCD. At this point, they’ve become pretty standard for various reasons. Many teams use something like this.

As Adam said, the relatively poor tolerances in tubing makes bearing blocks on the inside difficult. The tubing from McMaster-Carr has tolerances of .044" for the outside dimensions, and it’s probably much worse for the inside.

One benefit of the standard method (linked above) is that you can put a CAM on the pointed ends for tensioning.

The only CAM tensioners I’ve seen appear to be very difficult to machine on a manual mill and very custom. How do you approach the tensioner?

A cam could be square. Or you could sand a radius into it. It doesn’t need to be as fancy as what we make, for example. You just need something with a non-constant radius. They don’t even need to all be perfectly the same since you’re not going to get the exact same tension across all your chain runs.

For our chain tensioner cams we used a ~1/4" thick piece of 3/4" or 1" (I don’t remember which) steel shaft with a hole close to the edge and welded a #10/32 socket head alan bolt into the hole.

Once you rotate the cam so the chains are properly tensioned, how do you lock the cam in that position?

We have a lock nut on the other side that is tightened down, but that is less important than tightening the bearing block together from what I’ve seen.

The cam has a tapped hole in it. You just tighten it down and then tighten the bearing block.

how often do you need to re-tighten the chains or does it typically stay in place all season after you tighten them the first time

we tightened ours whenever they felt loose, which occured often after a pushing match

The bearing blocks stay in place after properly tightening them and the cam, if that’s what you’re asking.

The only reason you would need to re-tension is to deal with the chain stretching slightly over time as it loosens up.

Thanks for all the explanation. I never realized that the sideplates actually clamped the bearing block in place. The cam tensioners make a lot more sense now.

Usually the side plates actually ARE the bearing blocks. The bearings are in the two side plates which fasten together from opposite sides of the tubing.

It sounds like there are two common ways to create the bearing block assembly.

  1. Use two sideplates and a block of aluminum. The bearings go in the aluminum block, the sideplates hold it all together and clamp it in place. The machining for this setup is relatively simple.
  2. The two sideplates become the bearing block and are constrained coaxially with a short piece of thick walled tubing that connects them. The machining for this setup is comparatively complex.

Is that a fair statement? If so, what are the benefits to method 2?

I’ve never actually seen #1.

The Team 221 “Universal Chassis” uses this design.

This is a neat concept along the same vein.

We run 1. CAD in sig. 09 was unique, 10 and 11 were new design.

Given that those already have to be CNC machined there’s not a lot of benefit to doing it that way than the way we do ours.