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Rd400 Chassis Mods

RD400 Chassis Mods By Clinton Whitehouse Chassis Modifications For Racing An RD400 In 1983 at the Willow Springs AMA Superbike (1000cc) Fred Merkel was on the pole with a 1:34 plus lap time, I did a 1:39.01 on an AFM Modified Production legal RD400. AFM Mod Prod rules required the use of stock exhaust system, stock carburetors, a stock frame, and brake system. I believe that a difference of less than four seconds between an AMA Super Bike and my RD400 makes me somewhat of an expert on RD's. I a

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  RD400 Chassis Mods By Clinton Whitehouse Chassis Modifications For Racing An RD400 In 1983 at the Willow Springs AMA Superbike (1000cc) Fred Merkel was on thepole with a 1:34 plus lap time, I did a 1:39.01 on an AFM Modified Productionlegal RD400. AFM Mod Prod rules required the use of stock exhaust system,stock carburetors, a stock frame, and brake system. I believe that a difference of less than four seconds between an AMA Super Bike and my RD400 makes mesomewhat of an expert on RD's. I am sure I'm not that much better than Fred. Ihave won well over one hundred trophies with my RD400 in 450MP, 450SS,600SS, F1, F2, and other classes. Although the RD chassis will never be up to modern standards, it can be quiteserviceable. One of the biggest secrets to making an RD handle, believe if or not,is weight distribution. When the R-5 (precursor to the RD350) was designed, tiretechnology required most of the weight to be on the rear wheel. With moderntires (and not so modern tires) the bike will work much better with modern weightdistribution. The RD400 addressed this problem by lengthening the swing armand moving the engine forward a little. This is one of the advantages of theRD400 over the RD350 but even with this advantage you need to move your body as far forward as possible. This is why I run a stock tank, foot pegs that areclose to the swing arm pivot, and clubman bars instead of clip-ons. The TD-3tank, standard rear sets, and clip-ons look cool, (and are easy to do) but they willprevent you from climbing over the front wheel as you need to in order to obtainmaximum cornering speed. Clip-ons are also too short to give the requiredleverage.When CMMRA started a Formula RD class at The Streets of Willow Springs, Iresurrected my old RD. Racing at The Streets I had no handling problems at all,but when I took it to the big track, it just about scared me to death. The highspeed turns two and eight caused a very disconcerting weave - wobble. Iremembered from my experience in the early 80's that RD's had to have aperfectly straight frame to handle well, so the frame went off to Dr. Johns. His isthe only frame shop I trust, and he is reasonably priced. Normally he chargesvery little or nothing if the frame is not bent. If you are not sure your bike isstraight call him. New bikes that have not been crashed are not always straight.For example, my YZF1000R1 race bike had a high speed head shake until Icrashed it and had Dr. John straighten it. Now it doesn't. Therefore I took the RDto Dr. John, and can now ride it at the big track. Another common mistake is running fork oil that's too heavy. With the stockRD400 dampening rods I like 10 weight or at most 15 weight fork oil. I havetalked to guys that run 30 weight! I think that two things are going on here. First,  it's the old stiffer is better theory. Second, people are trying to make up for sacked out, too soft springs. I am currently using TZ D model dampening rods,(but have run stock rods without any disadvantage) with 7.5 weight oil. I run a _____kg/cm spring with about 20 mm of sag. I have ordered Race Tech goldvalves, but haven't tried them yet.Tapered roller steering head bearings are not absolutely necessary, but they arewell worth the money. Modern tires will impose loads that will force you to tightenor replace the ball bearings every race meet. The swing arm pivot definitelyneeds attention. If you haven't put after market bushings or roller bearings in, doit! Either bronze bushings or roller bearings will work fine. Either way, make sureit is shimmed correctly so it doesn't bind or have excessive side play.The front fender is a good fork brace and it is free. You may have to grind theinside a little for tire clearance. I don't normally run an after market brace, but if you do make sure it is not binding the front fork anywhere in its travel. Do this bymoving the fork up and down with the springs out, and the brace, front fender,and front wheel bolted up the way you will run it. Obviously you will need to havethe front end off the ground to do this.What the RD400's wheels lack in width they make up with their immense weight.Improving this on the front is easy as the RD350 wheel will bolt right up. It is a lotlighter and you can lace up any rim width you want. I usually use a WM-3 (2.15in) if the rules allow. Old TZ250 (pre H model) wire front wheels will already havean aluminum WM-3 or WM-4 rim, so if you can find one and it is legal in your class go for it. These are more common than you might think because a lot of people put cast wheels on their TZ's. Even if you are limited to stock width rims,use a wire wheel as it is lighter. The 79 Daytona front end has a wider, lighter front wheel (1976 to 1978 1.60 inch, 1979 1.85 inch) and the fork tubes are35mm compared to the early model's 34mm. The down side is it has a terriblefront brake caliper. If you are running this front end and the rules allow, adapt adifferent caliper. If the rules preclude this, run the 76-78 front end so you will atleast have some front brake.In the rear the Daytona swing arm, wheel and brake are a big advantage. Thewheel is wider (2.15 compared to 1.85) and all the components are lighter. If youare running the 76 to 78 rear end you have limited options. There was an RD400with wire wheels. I believe it was made for the Japanese market. I have seen 3 or 4 of these over the years, so they are out there. It uses the standard brake andsprocket. Chances are, since we're trying to work with a tight budget, most of uswill be forced to use the heavy narrow stock rear wheel. This is not so badbecause there is a good tire that will work well with the 1.85 inch or 2.15 inch rim.It is the Avon AM23 130/65 18. Do not confuse this with the AM23 130/70 18 tire.The 130/65 is a vintage racing (DOT approved) tire designed for the 2.15 rim, butwill also work on the 1.85 rim. This tire has amazing traction and feel. It is at leastequal to a 591 or Metzler equip FZ400 (that uses the stock rim). I am still looking  for the perfect front tire. I have tried the Metzler 100/80 18, 110/70 18 and Dunlap100/80 18 591. They all chatter at turn-in until you get on the power, but the100/80 18 Metzler chatters the least of these three. I recently tried Avon's racecompound tires in the 90/90/18 and 110/80/18 sizes. The 90/90 pushed the frontend, and had no feel, while still chattering. The 110/80 stuck well and had a littleless chatter than anything else I have tried. Front wheel chatter is the biggestobstacle to improving lap time at Willow Springs main track. On lower speedturns such as you will find at The Streets Of Willow Springs I have little or noproblem with chatter. The final chassis modification I will talk about seems like a step backward. In what seemslike a counter-productive step you will have to grind off the side of the bracing in the front part of the swing arm to fit the larger tires that I recommend. Also be careful not to touchthe swing arm tube itself. You would think this would ruin the handling but when I first didit in 1981 I could tell no difference in rigidity. I guess when the frame and fork flex soeasily it doesn't matter if you lose a little rigidity in the swing arm. The main thing is thatwith old flexible frames like RD's have, you just gotta ride smooth, have a straight frame,and have the suspension as close to right as humanly possible.The rear suspension is easy albeit expensive. Just bite the bullet and order WorksPerformance shocks that are 13.5 in long. I haven't tried every shock on the market, butWorks Performance really has a handle on twin shock technology. Their shocks are magiccompared to anything I have tried.