Cylinder Works Big Bore Yamaha YFZ478R: Reviving an R on a budget.

Right out of the crate, Yamaha’s YFZ450R is one of the most effective high performance quads ever offered. It’s a monster that delivers devastating power and race ready suspension straight from the dealer. All it requires is gas, a rider and regular maintenance. Some riders have so much fun with the Yamaha’s performance they forget about the maintenance. If that goes on too long, even a machine as rugged as the YFZ450R will suffer.

We found a 2009 YFZ that had seen an incredible number of hours of racing, trail riding and duning with astoundingly little care. The cylinder and piston were worn from use and sucking dirt from an air filter that was seldom cleaned. Amazingly, the head, bottom end and transmission survived too few oil changes, but the cams were nearly history. The Yamaha’s amazing fully adjustable shocks had never seen an oil change since new, and had lost much of their damping.

IT’S A RESCUE
A sophisticated race machine like a YFZ450R is a terrible thing to waste, but rebuilding one can be expensive, so we searched for ways to restore its performance affordably. With parts from Cylinder Works, Hot Cams, and shock service from Race Tech, we got the Yamaha making more power and handling better than ever for less than we would have spent replacing the worn items with stock parts.

MOTOR REVIVAL
Modern racing four strokes produce amazing power, but the engine parts are highly stressed, high tech components. That means can only stand so many hours of use and they’re not cheap. Rebuilding a tired race engine can run into money if you buy original parts individually. Most dealers charge $310 and up for the stock YFZ450R cylinder alone and around $100 for the bare piston. Cylinder Works’ big bore, 478cc cylinder kit for the Yamaha gave us a way to boost power with the top end rebuild and it comes with a new, matched piston and cylinder plus rings, clips, piston pin and gaskets for $650. Cylinder Works also sells standard bore cylinder kits for $559. Parapros Racing handled the engine assembly and made sure all the tolerances were correct.

Since the YFZ we were working with needed cams, we went with Hot Cams Stage 3 drop in replacements. They’re each about $50 more expensive than stock cams, but they seriously pump up the Yamaha’s mid to top end power. They also work with the stock valve springs, so they save money and shop time compared to more radical cams that call for firmer valve springs.

We added an FMF Titanium 4.1 exhaust and a Uni Two Stage filter and removed the airbox lid to let our modified YFZ breathe without restriction. Tuning a big bore engine with high performance cams and a free flowing exhaust and intake used to be a job for experts only. Dynojet’s Power Commander V  for the YFZ made it simple. We selected a map from Dynojet’s website that matched the modifications we added to the Yamaha and the YFZ was running at full potential with no fuss. The customized fuel map makes sure engine gets the proper amount of fuel to compensate for the improved airflow from the modifications.

SUSPENSION SALVATION
The neglected YFZ’s engine saw very little maintenance since new, but its suspension hadn’t been serviced at all since 2009! Race Tech replaced the worn out oil and worn seals in the stock shocks and installed new Race Tech Gold Valves with valving and springs customized for our rider’s weight, riding syle and riding conditions. Race Tech’s Race Series Conversion is an economical alternative to buying new aftermarket shocks and you get to enjoy suspension set up specifically for you.

THAT NEW QUAD FEELING
Looking at the restored YFZ478R, you’d never guess that it started out as a beaten down 2009. It starts so easily and runs so well just cruising around that it doesn’t even seem like a highly modified machine at first. That all changes once you stab the throttle. The revs soar and the Yamaha pulls so hard you have to hang on and focus to cope with its acceleration. The power is much stronger than a standard YFZ450R and it’s also broader, with a more solid pull off the bottom. The YFZ’s characteristic quick building, long lasting mid to top hit is still there, but the power is much bigger. This thing is an amazing weapon on a track for riders who can use the power, and it would be ideal for dune riding where there’s always a need for more muscle. The engine’s clean, predictable response even lets it work fine for trail riding, and you have the fun of pulling the trigger on the big top end rush in the wide open spaces.

Riding Race Tech’s modified suspension is an education on how much better properly tuned shock valving can be than stock. The YFZ450R’s shocks are among the best stock components on any ATV, but the stock valving makes the initial travel uncomfortably firm. Race Tech’s Race Series conversion gives the stock shocks the smooth, compliant ride expensive aftermarket race shocks are known for, with the high level of bottoming resistance the YFZ needs for race conditions.

The greatest thing about the restored YFZ478R is, it doesn’t just feel like a new 450; it feels like a new, different, better YFZ model. Getting that new quad feeling, with new power to master and better handling to control it makes riding anywhere seem new and more exciting, and it’s a whole lot less expensive than a new machine.

Cylinder Works
www.cylinder-works.com
515-251-4070
+3mm Big bore
Cylinder Kit 478cc – $649.95
Includes Forged Vertex Piston
and Cometic Top-End gasket kit

Hot Cams
www.hotcamsinc.com
515-402-8200
Stage 3 cams no springs required 4237-3IN Intake – $199.95
Stage 3 cams no springs required 4238-3E Exhaust – $199.95

FMF Racing
www.fmfracing.com
310-631-4363
Ti Factotry 4.1 system – $599.99

Dynojet Research Inc.
www.dynojet.com
800-992-3525
Power Commander V – $379.95

Parapros racing
www.paraprosracing.com
951-544-0882
Engine assembly

Uni Filter
www.unifilter.com
714-535-6933
Two stage Air Filter
(for GYTR mod) – $37.95

CV4
www.cv4.net
800-874-1223
Formed Silicone Coolant hoses

Renthal
www.renthal.com
877-736-8425
Stock front – $25.95
Rear sprocket – $64.95
R1 Works Chain – $81.95
Fat bars – $89.95
ATV  grips

DeCal Works
www.decalmx.com
815-784-4000
Full kit  (Backgrounds not included)  $ 199.00, Backgrounds to match $ 69.95

Works Connection
www.worksconnection.com
800-349-1475
Elite Perch Body – $79.95
Elite Perch Thumbwhee – $37.95
Elite Perch Lever – $37.95
Tach/Hour meter – $37.95
Hour Meter Mount – $14.95
Rear brake block off – $19.95

Moto Seat
www.motoseat.com
951-258-5229
Custom Cool seat cover

Houser Racing
www.houser-racing.com
877-646-3278
+1” Stem – $239
1 1/8” Handle Bar Clamp – $89

Pro Armor
www.proarmor.com
951-343-9270
Revolution Nerf Bars with Heel Guard Nets – $419.95
Pro MX Bumper – $129.95
Billet Rotor Guard – $159.95
Billet Sprocket Guard – $139.95
Pro Series Kill Switch – $34.95

Silkoleen
www.silkoleneusa.com
817-581-8616
Lubricants and Oil

Race Tech
www. racetech.com
951-279-6655
Race Series Conversion, front shocks – $720
Race Series Conversion, rear shock – $520

STI Tire and Wheel
www.stitireandwheel.com
318-255-0049
STI Tech 4 MX Tires
Front: 20×6-10 – $45.95
Rear: 18×10-8 – $59.95
STI Pro-Lite Alloy Wheels
Front:   10×5 – $56.95
Rear:   8×8 – $46.95