Rear wheel vertical alignment - '75 R90S

[Dave Backmarker]

I now have about 300 miles on my restored R90S and my son (more observant and better eyesight than his father) noticed the rear wheel tilts a bit at the top. From behind the top skews to the left by a degree or so. Our current thinking is a bent swingarm? At first we were thinking that a bent sub-frame might be putting enough pressure on the shocks to skew the swingarm but that doesn't seem likely. Any thoughts?

DaveM 1975 R90S, 2000 R1100RT

[StephenB]

If you can see it it's more than a degree!

Couple of questions/ideas:
- is your (optical) reference straight/perpendicular/parallel?
- Is the bearing stack installed correctly?
- if the swingarm is tweaked, the axle won't go through easily (I don't think the swingarm is bent)
- does your bike track straight when you remove your hands from the handlebar?
- is there any axial play at the wheel?
- Are the splines in good shape or completely gone?

[Major Softie]

What makes you think the rear wheel is not aligned. Aligned with what? If it appears to be out of alignment with the subframe, a tweaked subframe would seem more likely.

[Dave Backmarker]

StephenB and Major Softie,
Both excellent replies and ideas!!! Thank you! Yes, I know most people can't see a one degree deviation. So far this is using our not-so calibrated eyeballs. Mea culpa.

To Major Softie's question: Aligned with what? With the front wheel. We leveled the front, blocked the front and then eyeballed the rear. WHAT we're looking at in the back is to see how square the the rear wheel is with the ground. Not very precise yet, but we've been dreaming up ways to create frame references so we can check if the wheel really is out of vertical. My laser level with magnets will likely play a role.

To StephenB's questions:
- I've not re-installed the bearing stack. Good point.
- The rear axle installs beautifully, alignment is spot on.
- I haven't tried a no-hands test. Good idea.
- Axial play. I can check this with a dial indicator. I think you're hinting that maybe the wheel is bent.

Thanks again for the very helpful ideas.

DaveM

[Max Headroom]

Dave, if your wheel was bent, the vertical misalignment wouldn't be constant and it would be easy to spot simply by rotating the wheel by hand.

[Major Softie]

It's very hard to get the front wheel perfectly straight so that you can really compare it with the rear. If you used two big triangles to mount the front wheel straight, then you could check if the rear is straight as well. Probably a whole lot easier for a pro with a jig to check.

Then there's the question of just how perfect other bikes would actually measure out...

[Major Softie]

Oh, that could still hold the wheel straight up and down but not have the wheel straight in line with the rear. Damn I need an edit button.

[StephenB]

Front and rear wheel can be out of plane and slightly misalignment without any illeffect or reason. My rear is even laced 1/4" offcenter, can't feel the difference with my uncalibrated buttmeter. If the tracks straight without hands, you don't have a shimmy (=wobble) at low or high speed, your rear wheel has neither radial nor axial backlash, your swingarm and steering head bearing have 9-12Nm preload (not just zero play!) and all planets are aligned... you don't have a problem ... is my best guess without having looked at it. If there is an seasoned Airhead in your area s/he might be able to help inspectingif you're not sure.

[Roy Gavin]

Everything made has production tolerances, and two or three degrees out would probably be well within OEM spec.

If you have a local frame alignment specialist give him a call - he will probably tell you to start worrying when it is well past 10 degrees.

I understand the K bikes were the worst - some are a long way out, but most owners have never noticed.