Cycle News is a weekly magazine that covers all aspects of motorcycling including Supercross, Motocross and MotoGP as well as new motorcycles
Issue link: https://magazine.cyclenews.com/i/126402
KSI's new Mk. II 450cc Honda four- stroke MXer. The first competitive thumper to enter the two-stroke wars By Jim Gianatsis - The special "interest four-stroke motocrossers which I've tested in the past for Cycle News, Bengt Aberg's Hallman-Yamaha 500cc and CCM's 580cc monster, were unique bikes. They very definitely behaved and performed like the heavyweight four -stroke motocrossers they , . " were. For racmg m four-strokeo~y 24 classes you couldn't ask for bett~r bikes , but compared to the latest In two-stroke motocross technology. they jus~ weren't co~petitive. Their high weight coupled WIththe lack of needed engine response restricted them to smoother and less demanding courses . But just when I was labeling all four-stroke motocrossers as uncompetitive dinosaurs. Knobby Shop International. down by San Diego , CA. thought they could make a liar out of me with their latest piece of exotica. They did. KSl's new Mk. II 450cc Honda thumper is the first fourstroke motocrosser I've ever tested that I could classify as competitive against the latest factory two-strokes in National caliber competition. The reasons !iy the KSI th umper is such a hot machine are simple: a ready to roll weight ?f 228 pou~ds with a low . center of gra:--Ity, and a blg-bo~e 450cc Honda engine that snaps Its way through the powerband like a front. wheel -popping two-stroke. Built in England to Alan Greenwood's exacting specifications, the original Mk. I Knobby Shop International frame kit for XL-250/ 350 Hondas first introduced in 1977 has been revised. The new Mk. II frame kit incorporates all the changes and improvements learned since the original frame kit was introduced. It is also suited "to meet the increases in suspension travel , with our test bike sporting 11 inches of travel at each end provided by Simons forks and cantilever-positioned Fox AirShox. Built of Reynolds 531 chromoly tubing which is beautifully chrome plated, the KSI Mk . II frame is completely new and features a new ca ritile ~r' sWlngarm wltll slronger pivot mounts and beefing up around the steering head . foot pegs and engine mount areas. A new rear brake lever assembly. more reliable and with better lever action is incorporated and " designed for a full -floating rear brake now. Where there was none before, a new four-bolt head brace for the engine helps cut down on engine vibration and stiffens up the chassis. Also redesigned are the new fiberglass tank, airbox , under seat panel and the FIM style side number panels. The suspension incorporates the best available accessory components with .Simons air /spring forks up front offenng 11 inches of travel on our test bike . The shocks are 15.12 inch AirShox. two of which are mounted in parallel laydown fashion under the seat to work with the cantilever swingarm to produce II inches of wheel travel. An increase in travel to the 12 inch range could probably be accomplished quite easily with longer available Simons forks and AirShox. If you have your own XL·250 or 350 Honda to play with , the basic frame kit from Knobby Shop will run you $1170 . This includes nearly everything you'll need with the exception of the "suspension components. Included in t e kit are frame, swingarm., exhaust pIpe , airbox and filter, seat; side panels. rear axle. allo y tank, Timken tapered steering head bearings. fullfloating rear brake parts. chain guide and all necessary mounting hardware. For a total of about $2000 and an XL Honda for the engine and wheels you could have the classiest thumper on the block . Our test bike had recei ved the full race treatment with additional goodies like a Yamaha YZ conical front hub and Suzuki RM magnesium rear hub , . Buchanan's heavy duty spokes and Sun rims, Renthal handlebars . Petty fenders and Magura controls. Then the Honda XL . engine was race modified and bored out to' 450cc for competitive Open class horsepower. All totaled up. but not counting the cost of the engine which you would probably pick up pretty cheaply from the want ads in Cycle News , Knobby Shop could build you the bike pictured here for $3500. The price might seem a"little stiff. but it's comparable to the price of the CCM motocrosser complete, or building up a HallmanYamaha to comparable specifications. . The engine is a masterpiece of design built up by KSl's Frank Wilson. Beginning with a stock 348cc XL Honda. Frank uses a Powroll kit to get a new 77.3mm stroke and 86mm bore for a new displacement of 450cc . The