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/128075
Project Bike ,. Rick Peterson Motorsports YZ300 ~o YZ250 0n Viagra : The Rick • Peterson Moto rspor1s big- , bore-and-stroked YZ300 is the ultima te mot ocr osser 10r anyone wh o races in the Vet or Senio r cl asses at the ir local tra ck. Peterson does not con do ne signing up for a 250cc class on a VZ300, but because he produces so mu ch power out of his kits, he is someti mes known as " Cheaterson." By Matt Freema n Photos by Kit Palmer and Freeman ~ :::Iii !II !Ii lIii III ~ V :iii Q ,m 8l jl o ti o 28 or some, hitting the ripe old age of 30 can 'be rather horrifying. If [ } are a mo torcycle racer , howevyou er, chances are that you welcome the big th ree-a, for obvious rea so ns . You don't have to race against pesky 16yea r-o lds who fear no thing and are in better sha pe tha n yo u. In ad d ition, so me Vet racin g organizatio ns hold th eir own even ts on Ve t-friend ly tr acks th at lack monster ae rials, blind doubles and ene rgy-suc king stadi u m w hoops. Eve n bet ter, the Vet class is kind of a run-w ha tyou- brung competition, meaning th ere is n o br ea kd own for different eng ine di splacements. If yo u r KX25D-mounted budd y keeps beating you by a hair week after w eek, the answer is simple: Show up a t th e track with a CR500. It's perfectly legal in the Vet class. M ost g uys, yo u ng a nd o ld, w ou ld rather suffer the agony of defeat rather than wrestle a big open-classer around a motocross track, though. Rick Peterson, the owner of Rick Peterson Motorsports (RPM) is one of those guys, which is why RPM has become the culprit for building big-bore and stroker kits for most an y Japanese motocrosser imaginable. In the case of the over-3D racer who can 't get an edge on his buddy wit h the KX25D, the answer does not always have to be a new CR500 or even spending more time at th e gym. RPM has a sol ution to the monster-b ike dil emma, and it co mes in th e fo rm of a b ored a nd stro ked 25Dcc m achine. There is no sacrific e fo r handling or weig ht, just o ne hell of a power boo st when RPM's job is complete. Our 1999 YZ250 had been rid den in to the ground and was in d ire need of an e ngi ne rebuild. Th a t' s w hen Peterson himself stepped in and offered to build us a YZ300 to suit the lar gely ve t-popu - lated Cycle New s editorial department. He pleaded his case, stating that we'd love the power a nd t h a t the motor would be versatile enough to race a motocross one weekend, an off-road race the next and even a Super Motard .race later on if we got really ambitious. Once every over-3D person in the office registered a yea vote for the project, Peterson put the RMP crew to work. RPM w en t about building our YZ300 just like any other customer's. First, th e entire engi ne was disassembled and the int ernals inspected so that a list of parts that need ed repla cing , such as sea ls, gaskets, be arings a nd ge ars , co u ld be g ene ra te d. RPM ' s kit pri ces a lwa y s incl ude labor and the new Wiseco pi ston kit that they use for the project, but any o the r necessary replac ement parts are tacked on to th e bil l. A fter eve ry thi ng is clea ned RPM che mically stri ps the old platin g from the cylinder. Fro m there it gets complicated. On a YZ300 Big Bore and Stroker kit the inner a-ring groove in the cylinder is welded up and machined so that it is 5mm farther from the bore. The exhaust and cylinder skirts are also we lded and res ha ped just before the stock 66.4mm cyli nder is bored to 71mm. The cylinder is then ported and plated w ith a hard nickel-silicon-carbide liner. Next, th e cylinder is cryogenically ' frozen for 48 hours so th at the bore stays round w hen it ge ts hot. Mea nwhile, the power valves are sha ped a nd the head gets recharnfered. Moving to the bo ttom en d, the cra nk gets disassembled and the low er cra nk pin hole is re located 2mm farther fro m the cen ter of rotation. The procedure increases the stroke from 72mm to 76mm, the piston traveling 2mm lower an d hig her than its original journey. To balance th e crank, holes are drilled opposite the crank pin and tungsten slugs are inserted to ba lance the package. The cra nk is th en assembled with stock rod assembly and trued . To accept the lar ger stroke the cases are machined and then the engine is reassembled. The engine is then mounted in a jig and physically shifted through the gears an d kicked over to check actua l compression vs. the computer-generated estimate. Du ring the entire process, all balance, port timing, trapped-volume and compression-ratio specs are noted and kept in a perman ent file. The suggested jets were even install ed in o u r ca rb u re to r. RPM encourages all cus tomers to do the sa me. They also recommend th at customers include a lett er when they send in their engi ne that d escribes w hat type of riding theydo, the type of power they w ant, th e fuel th ey run, and th e pipe and reed s that th ey u se . RPM ha s it d o wn to a science . Th ey can tune the cylind er and head to suit any fuel r equirem ent s a n d a ll ridin g s ty les . Pet erson went th rough se vera l changes to make our two test rid ers happy. Th e irony of th e ultim at e Ve t-class