Cycle News - Archive Issues - 1970's

Preparing the for motocross & play How to set up the production RMs so they perform like the T rans-AMA winning works bikes. l/l l/l f- « z « e ::; -, > III l/l • o .. it fo iillIIIii "If yo~ w ant to go Grand Prix speed you must maintain Grand Prix maintenance schedules," said Tony DiStefano as he went over the spokes, bolts and tidbits of his practice RM. The new RMs are the only race bikes built for the average rider that are competitive 1 4 with works machinery, and yet sell for hundreds of dollars less than their European counterparts. But to win you must be there at the finish, not once but twice, and to do that eve n the fastest and most exotic racer must be gone over With a fine tooth comb. Th e suggested modification and work sequences suggested below are outlined for the RM series Suzukis, but are applicable and necessary for all makes of compe titive machine (wi th sp ecificat ion and technical changes). The Suzuki currently sits on top of the market place as the best buy, based on a broad spectrum of criteria, for anyone interested in winning, from the Novice to Expert rated rider. Without modification it can win , but with the suggested preparation it can keep on winning and winning for a longer time. Very few p arts on the RMs are the same as on the World Championship and Trans-AMA winning RN 37 0s as rid den by Roge r, Gerrit an d Tony Dee, but the $1,400 production bikes are so similar to the works bikes in design and performance that it would be totally. senseless to have the factory bike with its expensive parts and repairs. when the production brxes are available. The RM 250 and 370 bikes do have the same frame and suspension geometry, engine bore and stroke, and cylinder porting layout as the works bikes. The RMs actually have a few advantages over the works bikes. Their production parts are much more reliable than the hand built counterparts of the works bikes. The RM engines are actually better than the works RN and RH engines because the production RM engines are actually one design ste p ahead of what is in the factory machines. One fact that people won't believe unless they've had the chance to ride and see a works bike and a production bike race- side by side is that the productions RMs are faster. Ho nest. Also , the production bi kes weigh 3 or 4 pounds less than the works bikes. The frame As well as showing how to modify the RMs to make them more reliable an d competitive, much of this article deals wi th what should be con sid ered a weekly maintenance routine before going racing. The plastic airbox needs atten tion in that it restricts breathing and should be cut or drilled open on the right side, in such a way that the number anel still acts as a good sp lash shield. Make the hole abou t 2 inches high by 4 inches wide, up near the top frame member. The airfilter element which comes stock isn 't too good, and usually leaks around the base of the airbox, Reflace the filter with a Twin Air filter. I you can't get one of the new Twin Air Phase II elements with the outer sock, make y our own double sock filter out of a larger diameter Twin Air filter. Use the special Twin Air or Bel-Ray filter oil on the filter. Grease the base of the filter and the airbox filter mount very heavily with gre ase. It is difficult to get the first airfilter to seat properly at the airbox filter mount, so make sure the second filter overlaps the firs t filter enough to guarantee a good seal. Use two large diameter flat washers on the rear muffler bracket, where it moun ts to the frame , as an added safety feature to prevent the bracket cracking from vibration. Be sure that the gas tank is completely rubber mounted off of the frame tubes. It is possible for the stock rubber material to move and allow the frame to cause stress on the rear of the tank. Normally this can be prevented by ca refully securing the rubber cushions with electrical tape, although additional rubber attached to the tank provides an additional margin of safety . Race bike, or play bike, preparation is a lway s keyed to preventing problems rather than curing them. Disassemble and clean the footpegs weekly to assure they work properly. Crimp the ends of the springs on the muffler to prevent them from popping off. Don 't try welding the muffler onto the expansion chamber, or you'll never be able to get the chamber through the frame. Because the RMs have the longest travel rear suspensions of any motocross bike , some 8 1{2 inches, there can b e problems with swingarm flex and the chain being thrown off. The easiest way to correct both problems is with a swingarm which won't flex . The stock steel tube swingarm can probably be braced with gussets to prevent it from flexing, bu t the . better solu tion is to replace it with a monocoque alu minum swingarm as used on the factory works bikes. Three firms now build high quality accessory swingarms for the RMs. Rich Thorwaldson's Thor Enterprises has a works replica monacoque aluminum swingarm for $129, Bassett Racing Products has a Rex Staten tested alu minum model for $145 which includes titanium shock bo lts, and Motocross Center in Sunnyvale, California markets a 4130 chrome-moly swingarm with cam chain adjuster, chrome-moly axle and needle bearings for $124. All the swingarms are better than stock and prevent flex. Flex is the major problem of the stock RM. The swingarm and the airfilter are the two most important items to attend to. You can t b with e

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