After a bunch of work and several revisions, I finally got my alignment jig working OK (the tubes are straight to within .002", my camera not so much):
This setup basically aligns the rear axle with the LH stub-axle swingarm pivot, performing what's generally referred to as a 'thrust angle' alignment (drive axle perpendicular to vehicle centerline). No, it's not equivalent to a 3-axis frame alignment jig - not even close ! - but on my bikes at least, it's much more accurate than the swingarm hash marks.
It's pretty simple; one 10mm-O.D., 610mm (24") long tube each into the rear axle and swingarm-pivot centers, with two adjustable yokes that ride along these tubes to ensure they're parallel. Yoke adjustment is done by rotating the center hex rod, which has LH and RH threads into the inner yoke ends. The rear tube has a brass adaptor to fit the axle hole, while the front fits into the swingarm pivot as-is. To use it on the chain bike, I loosen the axle nut, lift the bike, insert the tubes, then adjust the yokes to fit the tube-center distance and slide it back and forth until I'm happy with the tubes' alignment (usually 2 or 3 passes). I then tighten up the axle nut most of the way, re-check the tubes, turn the axle adjuster(s) until they contact the axle sliders equally, then lower the bike and tighten the nut up fully. The belt bike is more difficult; the belt tension means the tube alignment must be done using the axle adjusters, not simply by hand using the tubes (OTOH, it doesn't have to be done very often). I do it during belt / chain adjustments, it adds about 5 minutes (chain) or 10-15 min. (belt) to the process.
It's interesting how my Zeros steer after being aligned with this jig. Before the alignment, they were what I thought of as 'normal', with one direction having slightly easier steering than the other and a tendency to wander just a little. Afterwards, the bikes held a straight line better and also had what felt like a slight 'power steering' effect, where my steering input caused the front wheel to move (or feel like it was moving) to the new line with what seemed like additional assistance. This effect was completely symmetrical, and faded out on the 'MX' after several chain adjustments - until I realigned it yesterday morning and the feeling returned. It was fairly subtle and only really noticeable on the street; in the dirt the main difference was much less difficulty staying centered in ruts without the tires 'climbing the walls', which was the main reason I started this PITA project to begin with.
It's amazing how precise the steering is now - I even find myself using the narrow raised areas
between ruts (@ 4" to 10" wide) which I avoided like the plague before.
If you don't have knobby tires, are certain your front and rear wheels share the same centerline, have a way to hold your front wheel absolutely straight, and know your tire edges/rims are true, there are plenty of string / straightedge / laser methods online that will give you some kind of result with far less effort than this. The ones I tried didn't work for me at all.
Here's the final combined diagram - it uses various scales, but each individual item is proportionate:
I got my metal (316 stainless tube & hex rod, 360 brass tube) from onlinemetals.com; they're expensive, but they sell in small quantities and can cut to order if needed. The two #82055062 yokes were from mscdirect.com (their larger #84258219 yokes will also work). The yoke extension tube is JB Welded to the outer side of the yoke arm, with the rod thru it & the yoke to keep it aligned while it hardens. I had two made up, but the jig works fine with just one (on the forward yoke).
Ray
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Topic: Rear Wheel Alignment Jig (Read 1823 times)