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Old 03-19-2012, 11:36 AM   #18
FJ_Kevin OP
Gnarly Adventurer
Joined: Dec 2010
Location: Maryland ==> originally from Long Island
Oddometer: 365
Haha... they're coming out of the woodwork now!

More about my rear wheel saga...

My original 1980 rear wheel was pretty much done for. Not only were the spokes rusty but I discovered a small crack in the rim. Apparently, it is not uncommon for these old rims to crack as I found out when searching for a replacement on ebay. Lots of “good” wheels were listed with cracked rims, jeeze.

It is also important to check the rim width when looking for a replacement. Keep in mind that the big bore bikes use a 2.50 x 18 rear rim. You would come up short with a YZ250 wheel as that one is only 2.15 x 18.

Eventually I found what was said to be an IT 490 wheel. Although the rim is silver, it is not the same as the one on my IT490. The IT490 has squarer edges and is supposed to be stronger and heavier than the YZ rim. This one has a silver 18 in rim of the type a YZ would have.

Perhaps it is a later, post gold rim, YZ490 model, I'm not sure. One thing in clear, it uses a “standard” type hub, not the z-spoke design.

In any case, it uses the larger diameter axle (like the 1981 465 and 490's as others have mentioned). Another difference is the number of wheel bearings used. The 1980 hub has a single cartridge wheel bearing in each side. The 1981 YZ465 and 490 hubs use two bearings on each side, very beefy!

The good news is that the wheel was in decent condition with good spokes. It also came with a brake plate and the axle assembly, including all the chain puller do dads.

Of course, using the later model hub with large axle in my 1980 swing arm took some doing. Several steps were required,

1) Mill open the axle slot in the swing arm. This was an awkward process as my mill is too small for this job. In the end, I simply bolted the arm to the table the best I could and took very light cuts until I was within 5 thou of the needed dimension. I then used a file to get the finished dimension. I only cut the bottom side of the axle slot. I used the “flats” of YZ490 chain adjuster spacers as a gauge to check my fit. The fit was kept tight across the slot to ensure the bottom side would remain parallel to the factory machined top side.

2) It turns out the 490 swing arm is thicker than the yz465 at the axle mounts. This can be seen in the different in the chain adjust spacers and the internal width of the adjusters themselves. The fix was to mill the width of the 490 spacers to match the 465 spacers. As for the adjusters, I simply squeezed them down in a vice to the necessary size. I left the end portion of the adjuster outside the vice jaws. This allowed the adjuster side plates to follow the threaded end tab to give a neater appearance.

3) Finally, I cut a new axle spacer for the left side. The right side needs no spacer. The 490 brake plate is different than the 465 plate (’80 or ’81) and the "spacer" is cast as part of the plate. In cutting the left side spacer I took care to keep the sprocket spaced off the arm exactly the same as on the 465 hub. I was willing to re-center the rim through spoke adjustment if needed. Fortunately, the wheel was well centered without having to do this.

With all of this said and done, plus some new bearings, I had the 490 wheel mounted and ready to go.

Here are the photos to go with the description.

First the ugly 1980 wheel. Note the studs in the hub to mount the sprocket. The '81 and 490 hubs use bolts that thread into the hub.

Next is a ugly 1981 wheel. These have the big axle and double bearings. I will re-lace with new spokes and rim in future.

And a nice clean YZ490 wheel test mounted in the 1980 arm

Milling the swingarm with very light cuts, final dimensioning by hand...

New All Balls rear wheel bearings. Note, bearing have seals on both sides, I like that!

Here are the axle adjuster spacers, left side is the 490 (too long), right is the 465.

Milling the 490 spacer...

Now they match!

Squeezed down 490 chain adjuster

More to come... but first,

Marty Moates at the Carlsbad USGP

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