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/126344
Desert sled '78: SeuIke's 598ee Pro-Tee Yamaha By Charles Morey One-tim e ruler of the western wastelands, the big bore fourstroke desert bike will never cease to exist - at least not as long as people like Jim Seulke ("sulky" like the horse racing rig) continues to express their preference for the mellower sound and torquier power that the intake / compression /ignition / exhaust m odels have to offer . Seu lke's Pro-Tee motor, a highlymodified 1977 TT500 Yamaha, provides the basis for a unique one-off off -road motorcycle. The motor, the front wheel assembly, the rear hub and rear wheel rim are all that were used from the original machine. The rest consists of selected aftermarket parts or , in the case of the '78 YZ Emodel front forks . parts from another Yamaha model. The Yamaha motor received a full Pro-Tee transformation from mild mannered 499cc trailbike powerplant to a 598cc cactus blaster. The original bore and stroke - 87mm X 84mm were pumped up to 90mm X 94mm specs with a Pro-Tee stroker crank assembly ($250 exchange) and 90mm piston kit ($37 .95). Both rod and Ug htwelght. long-legged and powerful, Seulke's Yama ha is the hot set-up. 22 piston are manufactured by Pro-Tee. The rod is machined from a 4130 forged billet. The piston increases the stock 9 : 1 compression ratio to 10: 1. Head porting and flow test ing ($65) . a Pro -Tee stroker cam ($79 .95 exchange) and their high performance valve spring kit ($ 19.95) all contribute to th e impressive power increase. Pro Tee's 38mm Mikuni carb kit, which includes the intake manifold , throttle cable, Barnett quarter-turn quick throttle and K&N air cleaner ($91) kee ps t he monster fed . The 1 ~ .. diameter Pro -Tee pipe ($44.95) ha nd les t he increased demands on the Fox AirShox. Dick Mann swingarm . exhaust system while adding its bit to th e overa ll power increase and weight savings. A high volume oil line kit ($8.95) improves lubrication efficiency on the higher-st ressed motor. The Pro -T ee people do all motor mods, including the cylinder bo re ($15) and a co mplete disassembly/ reassembly/installa tion ($80) . T heir la bo r brings the motor modi fication price to just a q uarter under $693. Seu1ke then put his killer motor into a Dick Mann MX frame a nd bol ted on the Yamaha YZ400E forks a nd Fox AirShox to bring the suspension up to cu rrent motocross standards. Pro-Tee chain tensioner, rollers , guides . case-saver and shock protector keep the chain out of trouble through the increased suspension movement while a cut-down Pro -Tee skid plate guards the cases . Additional bi ts and pieces incl ude a Gunnar Gasser thrott le, Preston Pett y fenders, a 3.00 X 21 Metzeler up front, a 4 .60 X 18 Du nlop Sports at the rear and heavier-d uty spokes on back . The heavily-padded seat is a on e-off custom item . While we used the bike, as Jim Seulke does , for a desert/trail bike. it also is a formidable four -stroke motocross machine . The bike is scheduled to contest the Dec . 10 CMC Four-Stroke Nationals ridden by Pro Tee's J on Clark. Negotiations for Rex Staten to ride it fell apart whe n Staten was ca lled upon to fu lfill ot her ob ligations. The desert sled lives on in a m uch improved form. If there had been bik es like this way back then , t wo strokes may have remained 6 minorit P ro-Tee, Inc. 282 Gemini B rea , CA 92621 714/738-0631 213 /697-6759