9/9/14

DT1 MX project

The swingarm is fitted to the bike, so now to fit the wheel to the swingarm. I was able to locate a stepped '77 RM250 axle for the swingarm, so that makes it an easy fit. The axle and right side adjuster spacer are 17mm, but steps down to 15mm for the left side. I'd had an XT500 wheel on the bike so I could move it around, but will be using a TT500 wheel on the finished bike. The TT500 wheel has a larger rear brake with a magnesium plate, and no cush drive. TT500 rims are 2.15" wide compared to 1.85" for the XT500. On a stock DT the brake stay anchors to the frame, so you have to use a wheel with a brake plate that pivots on a bushing, like the SC500 wheel I used on the DT flat tracker. Since the brake stay bolts to the RM swingarm, that isn't a problem here.
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The XT wheel that was on it has a 5.10 tire, and the TT has a smaller 4.10. I'll likely use something in between the two sizes on the finished bike.
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I spaced the wheel, and stuck a chain on to look for any problems. It won't be cut to length until final assembly since I'm not sure yet what size sprockets I'll be using.
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The stock DT brake actuator and rod don't even come close to fitting with the RM swingarm. I thought I'd see if it was possible to move it outside of the frame, so put an offset arm on the brake, and tacked a piece of steel on the brake pedal to see if it would work. Any suspension compression started to engage the brake, and the shape of the swingarm prevents the rod from being placed near the swingarm pivot like the stock actuator, so a rod was not going to work at all.
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A cable was the answer here, which is what Suzuki used on the RM. I dug out a couple rear brake cables and found a Suzuki T500 cable the right length, so tacked together some parts enough to see how this would work.
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I then removed the shocks to test it out.
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Even with the tire up into the fender, brake freeplay wasn't effected.
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Here is the cable stay I made to bolt to the brake plate, and I made one similar for the front.
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Here it is finished up.
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I also wanted to see how much slack I'd need to run to keep the chain from binding when the suspension is compressed to see if I'll need a tensioner. I think I'll be alright without one, but haven't decided for sure yet. The tension doesn't change as much as I'd thought it might. I'll also likely be using slightly shorter shocks on the finished bike than the TT500 shocks I'm using here for mock-up, which will make it even less of an issue. It isn't installed here, but I've got the rubber rub block for the top of the pivot area of the swingarm.
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Just some small details to work on and it'll be ready for teardown.
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9/1/14

DT3

I gave the old '73 DT3 a wash and wax, and installed a NOS Yamaha accessory fork brace I'd bought awhile back.
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