Sunday, June 2, 2013

XT500 quick change wheel

As you may remember, the last race of the 2012 season ended with a nasty high-side crash at OVRP. In the event, the muffler went into the rear wheel, breaking and bending spokes, and crushing the header pipe. I was forced to decide on either rebuilding the rear wheel, which was a lousy option because the drum brake was warped, so I'd need to lace a new drum hub up to the old rim, or switch over to a quick change rear wheel with a disc brake.

I got a good lead on a quick change wheel for sale, and wound up buying it this winter. It came with a nice Continental Dirt Track tire, but that tire is too wide to fit in my stock swing-arm, so I mounted my Goodyear and the fit is fine. It also came with an old 7/8" master cylinder, an axle and some spacers, and some other odds and ends. Fortunately, the spacers that it came with fit my stock axle, so once I determined the wheel would fit in my swing-arm, I just had to figure out spacing on the wheel, and how to mount up the master cylinder and caliper, and how they would affect the exhaust, which runs right under the right foot peg.

This is the new wheel, temporarily mounted so that I can move the bike in the shop. You can see where the exhaust runs under the old foot peg. At this point, I hadn't figured much out.

After some research online I found Cheney Engineering, this guy has answers for questions I didn't even know to ask! I called the shop and Jerry Cheney answered. He turned off the lathe, and spent the next half hour helping me with some of the products he sells. I had already purchased a caliper, so I needed a caliper hanger. Then he asked me what kind of master cylinder I was using. When I told him, he laughed and said he'd hoped everyone that had one of those old 7/8 cylinders had thrown 'em out 20 years ago. He wound up selling me this very tidy foot-peg/master cylinder/brake pedal/ mounting plate that would save me a bunch of time and head scratching...

I had to cut off the old foot-peg mount so that I could get the plate close to the frame. The plate had two mounting holes for the footpeg, so I'm using the rear mounting hole to bolt the plate to the old foot-peg mount, since it's threaded into the frame.

I needed to have another mounting point for the plate, and since the frame tapers away from the foot-peg mount, I made a spacer to take up the distance between the plate and the frame.

I wasn't sure how I would accomplish the upper mount. I had thought of a few ways to do it that involved welding and tapping threads. Then I decided to get some advice from Fred, since he's only got about twice or three times the experience that I have in fabrication. Probably four times. Anyway I showed him the stuff and my ideas, and he agreed that a through bolt would be the best, simplest and easiest way to do it.

Then he took me into his trailer and handed me the nut and bolt that would do the job. Surprisingly small, but he claims it's also surprisingly strong, and in fact his race cars are put together with this size hardware throughout.
I had to buy a new bolt for the lower foot-peg mount and grind it down so that it would clear the frame.

So here it is mounted in place. Once I got everything tight, I put my old exhaust pipe on to see if it would interfere with the pedal, and as I expected, it does. Then I sat on the bike to see how the pedal/foot-peg would feel, and discovered that the foot-peg feels fine, but the pedal feels too high, like I'd almost have to lift my boot off the peg to get my toe on the pedal. I can't rotate the plate because the foot-peg bolt hits the frame, so I may have to modify the pedal/master cylinder location. Nothing is as simple as it looks...

I'm still waiting on parts for the axle and caliper. Jerry sent me some stuff that didn't fit, so I sent him my axle and caliper, as well as some spacers, so he can make the correct stuff. I'll also have a sprocket for OVRP.

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