Monday, March 2, 2015

WR250R swingarm bearing replacement

The WR has four needle bearings in the main swingarm pivot, two on each side set to precise depths from each end. During disassembly and inspection I noticed the steel tubes that slide into the bearings had some wear. While they may have survived another season, I figured it was worth replacing them now while I have the time and everything's apart anyway.

I only found replacement bearing kits from Moose Racing and All Balls. The Moose kit was cheaper so I ordered it, but the package I received was labelled in fine print as being made by All Balls. Go figure.

Removing the old bearings

The outside bearings on each arm can be removed using a blind bearing puller like the one shown below. It's a handy kit and well worth the $150 to save hassle during inevitable bearing replacements on any two-wheeled (or more) toy.


Unfortunately, impact forces from using a bearing puller are not nice for precision aluminum parts like the swingarm. So to remove the inner bearings, I used my little arbor press to push out the inner bearings with an aluminum cylinder I turned on the lathe to just fit inside the tube. The bearings came out like butter, no impact needed.

Pressing the new bearings

Amazingly, the swingarm fits perfectly within the frame of my arbor press. This means I can press all four bearings in to the correct depth using a simple tool.

The WR manual says the inner bearings need to be pressed in 8.5mm from the inside end, and the outer bearings 15mm from the outside end. I wrote these numbers on the swingarm. On my lathe, I machined a simple aluminum cylinder with a cap to push on the bearing. The part that goes into the tube was machined to 8.5 mm long, and then I made a short piece that was 6.5 mm long (labelled 15 mm in the photo). When stacked together, they give 15mm of pushing depth.


Now it's a simple matter of pressing the bearings. 

First the inside bearings. After applying some grease to the bearing exterior and tube, I carefully started them into position on a chunk of aluminum and then pressed them flush with the end, using the cap to push on the swingarm. 



Then I swapped the locations of the tool and aluminum bar, and pressed again so the tool pushed the bearing in another 8.5 mm from the end. 


Same process for the outer bearings, except I added the little 6.5mm stacker piece to press the full 15mm.

If you don't have an arbor press, it's well worth the $70 to be able to precisely apply these kinds of forces. It only took about 15 minutes to press in all four bearings, nothing misaligned or damaged.

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