For this edition of Classic Steel, we are going to take a look back at Yamaha’s all-new YZ490 for 1986.
All-new from the ground up, the redesigned 1986 YZ490 offered riders a selection of old-school simplicity and new-school technology. Photo Credit: Yamaha
In 1985, Yamaha pulled off one of the most impressive upsets in motocross history when Broc Glover bested David Bailey and the powerhouse factory Honda squad on his nearly stock Yamaha YZ490. The year before, Yamaha made the surprising decision to abandon their costly “works” bike program in favor of racing production-based machines in the US. This was at a time before the “Production Rule” when all the race teams were campaigning “one-off” prototype machines that shared very little with what a consumer would find on the showroom floor.
In 1985, Broc Glover took a nearly stock YZ490 to the 500 National motocross title. Photo Credit: Motocross Action
Broc’s air-cooled production YZ490 cost a mere fraction of the exotic liquid-cooled RC500 campaigned by David Bailey, but somehow the Golden Boy prevailed. At the time, the production YZ490 was not even the best stock bike in the 500 division. Its air-cooling and four-speed transmission put it at a distinct disadvantage against the liquid-cooled five-speed powerplants found on the Honda CR500R, Kawasaki KX500, and KTM’s 500MX. All three offered less vibration, more consistent jetting, and longer-lasting power. The YZ’s stock suspension was also very poor, with wimpy springs, poor damping, and a wicked propensity to kick in the rough. Off-road riders liked the rugged simplicity and reliability of the YZ’s air-cooled motor but found its four-speed transmission limiting. Glover’s 1985 500 championship gave Yamaha’s PR department a lot to crow about, but any realistic assessment of the stock YZ490 pointed to a machine in serious need of an upgrade.
An all-new frame for 1986 offered stronger construction and a repositioned rear suspension system. Photo Credit: Yamaha
After taking drubbings in all the major shootouts of 1985, Yamaha went back to the drawing board for 1986. The YZ490 adopted an all-new chassis with additional gusseting, stronger tubing, and a repositioned rear suspension system. The redesigned Mono Cross rear lowered the shock’s position on the chassis, moved the linkage to below the swingarm, and placed the damper at a more upright angle. A new swingarm was stronger and featured a new mounting to accommodate the repositioned shock. An all-new damper was spec’d that Yamaha claimed was designed by their partner Öhlins. The “Öhlins-style” shock was built for Yamaha by Showa and continued to employ Yamaha’s unique Brake Actuated Suspension System (BASS) to reduce compression damping under braking. Overall travel was set at 12” with a full range of compression and rebound adjustments available.
By 1986, all of Yamaha’s competition had moved on to liquid cooling for their 500-class machines. By sticking to air cooling, Yamaha kept their cost down and appealed to off-roaders and casual riders who did not want or need the added complexity of radiators to crush or a water pump to damage. Photo Credit: Motocross Action
Up front, the YZ490 continued to use a set of 43mm conventional Kayaba damper rod forks. At the time, these were considered quite stout and were the same size as the silverware found on all the Japanese full-sized machines. In 1985, these forks had been dismal performers, so for 1986 Yamaha dialed up all-new internals to improve their action. Unlike Honda’s new Showa forks, the YZ retained a traditional damper rod to handle the oil flow within the forks. At the time, Yamaha did not feel the additional cost of Honda’s works-style cartridge damper system was worth the gain in performance. While the YZ did not get the Honda’s wave washers, it did receive all-new valving that increased compression damping by 10 percent and bumped up rebound control by 15 percent. The spring rates in the forks were also increased by going from 0.325 kg/mm springs to a set of stouter 0.375 kg/mm coils. Internally, the forks were also upgraded by adding an Alumite coating to the sliders. This ultra-hard coating reduced friction and lessened particle contamination of the oil from erosion of the sliders. Total travel was set at 12” with external adjustments available for air pressure and compression damping.
In the late seventies “Boost Bottles” were all the rage but by 1986 they had all but disappeared from motocross design. Yamaha’s version was called the Yamaha Energy Induction System (YEIS) and it started appearing on YZs in 1981. The theory behind the YEIS was to provide a reservoir for any excess fuel and air not used on the intake cycle. The YZ490 was the last motocross machine to have a boost bottle as standard equipment, and it continued in use on the 490 until its retirement in 1990. Photo Credit: Iconic Motorbikes
Paired with the all-new chassis was redesigned bodywork that improved ergonomics greatly. In 1985, the YZ490 featured a low-slung riding position that made it a chore to get out of its giant marshmallow of a saddle and difficult to slide forward in turns. While none of the 1985 500 class were anything close to svelte, the YZ490’s wide bodywork, scooped seat, and pudgy tank made it feel more heavy and unwieldy than its 230 pounds would have indicated.
The Open class was always about big power and big fun and in 1986 there was a huge variety of two and four-stroke big-bores from the USA, Europe, and Japan looking to scratch that high-horsepower itch. Photo Credit: Dirt Bike
For 1986, Yamaha slimmed down and flattened out the riding position with an all-new seat, tank, and side panels. The new tank offered 0.4 gallons more fuel than the 1985 while still featuring a thinner profile at the seat/tank junction. The repositioned shock allowed Yamaha to redesign the airbox and reshape the side plates for a sleeker midsection. The all-new seat was slightly shorter to match the shape of the new tank but featured a flatter profile on top to facilitate easier rider movement. The front and rear fenders looked identical to 1985, but the rear did feature a slight update to work with the redesigned frame.
In 1986, Yamaha redesigned their Mono Cross rear suspension to sit lower on the chassis for improved weight distribution and performance. Photo Credit: Yamaha
Up front, an all-new disc brake reduced the size of the rotor to make it less vulnerable to damage while a redesigned twin-piston caliper offered increased bite through the use of grippier pads. In the rear, the YZ continued to employ an old-school drum for braking duties. A new front wheel finally eliminated the failure-prone “Z-spokes” Yamaha had employed since 1984.
All-new bodywork for 1986 flattened the riding position and slimmed the midsection of the YZ considerably. Photo Credit: MOTOCross
On the motor front, Yamaha took a conservative approach in 1986. By this point, both Honda and Kawasaki had moved to liquid cooling for their Open class machines, with Kawasaki even adding their variable exhaust valve KIPS system to their biggest KX. At the time, Yamaha claimed both advances were unnecessary expenses on a 500. They believed that 500s already had too much power for most riders and that the added complexity, cost, and weight of liquid cooling and a power valve system were not justifiable in a low-volume product.
Yamaha’s Brake Actuated Suspension System (BASS) used a cable-operated valve to reduce compression under braking. While it was an innovative idea, many riders felt it did very little to improve the performance of the YZ’s rear end. Photo Credit: Yamaha
While the new YZ490 did not receive the smaller YZ’s YPVS and liquid cooling for 1986, it did adopt several changes aimed at improving its versatility and performance. The most dramatic of these upgrades was an all-new transmission that finally added a fifth gear to the big Why-Zed. The new cogbox tightened up the ratios and improved the YZ’s versatility away from the track. The top end remained steel-lined and air-cooled which many off-roaders appreciated. That meant the cylinder could be bored in the event of a seizure and there were no radiators to smash or boil over. Changes for 1986 included an all-new cylinder casting with reinforcements around the base to improve sealing and prevent the cracking around the cylinder studs that had plagued some earlier 490s. Revamped porting, a deeper-breathing airbox, and all-new fiber reeds aimed to beef up low-to-mid response for 1986. The carburetor remained a massive 40mm round-slide Mikuni that Yamaha felt provided a smoother power delivery than some of the newer flat-slide mixers. The bore, stroke, and displacement remained unchanged from 1985 with the YZ clocking in at 87 x 82mm and 487cc.
The YZ490 may have been a bit old-fashioned in the motor department but the rest of the machine was quite up to date. The new layout was slim and comfortable and the revamped chassis handled well. Photo Credit: Dirt Bike
On the track, the revamped YZ490 was substantially improved in almost every way. The new layout was more comfortable with a more “sit on” feel than the previous 490s. Despite clocking in at the same claimed 224 pounds as in 1985, the new slimmer bodywork and improved riding position made the revamped YZ490 feel substantially lighter on the track. The flatter seat and narrower tank made it far easier to move around and weight the front end in turns as well. This aided cornering and the YZ was plenty happy to dive to the inside line if available. It was not as nimble in the twisties as carvers like the CR, but at speed, the YZ was far less anxiety-inducing than the red machine. Once you dialed up its new fifth gear, the YZ was rock solid and rarely shook its head. Airing the YZ out was more pleasant as well with its improved ergonomics. It was still a big and very powerful bike but the updated chassis and bodywork did wonders to make that size and power more manageable.
The YZ490’s unique BASS-equipped shock for 1986 featured an Öhlins design and Showa construction. Photo Credit: Motocross Action
On the suspension front, the ’86 YZ490 was a significant upgrade over the previous season. The redesigned Mono Cross rear suspension provided a much better ride in the rough and no longer bottomed out and kicked sideways on hard hits. The stock spring was in the ballpark for most riders and the Öhlins-designed shock did a very good job of taking the bite out of the track. Big hits and small chop were taken in stride, and it offered one of the smoothest and most well-sorted rides in the class. The BASS system remained but most riders felt it did very little to affect the shock’s performance. Overall, it was the best-performing YZ shock in a decade.
All of the Japanese 500s had their champions in 1986. Riders looking for the best forks and tons of hit were happiest on the explosive Honda. Riders hunting for the most technology and the widest powerband were likely to find satisfaction on the KIPS-equipped and dual-disced Kawasaki. If simplicity and versatility were your thing, then the air-cooled Yamaha had a lot to offer. Photo Credit: Dirt Bike.
Up front, the story was not quite as rosy for the new YZ. The revamped KYB forks were much improved over the dismal 1985 versions but still a significant step down from the Honda’s excellent Showa cartridge units. The stiffer springs and revamped valving were far more resistant to bottoming but their action remained disappointing overall. Big hits were taken well, but the forks were harsh and choppy on smaller obstacles. Sharp ledges and braking bumps that the Honda virtually ignored were transmitted directly to the rider’s wrist on the Yamaha. With some spring and oil weight fiddling their action improved somewhat, but they were never going to be as plush and comfy as the forks on the CR.
An all-new front brake for 1986 reduced the size of the front rotor and added a redesigned twin-piston caliper and grippier pads. Photo Credit: Yamaha
For most riders, the biggest bone of contention with the new-look YZ490 was its very old-look motor. The decision to eschew liquid cooling saved Yamaha some development dollars but it also led to several compromises in performance. By going to liquid cooling, the YZ’s rivals were able to use tighter tolerances within the motor, run higher compression, and jet their carburetors more precisely. The wide temperature changes an air-cooled motor endured during a long moto made it difficult to jet properly and this hindered the YZ’s performance. If you jetted it to run cleanly when cold, then you risked seizing the motor once it was hot. The motor’s internal parts also tended to expand and contract more than in a temperature-controlled top end, so the engineers had to factor these variations in when designing the cylinder, piston, rings, and head.
The YZ490’s updated 43mm forks for ’86 featured new valving, stiffer springs, and a slick Alumite coating. Their performance on the track was much better than the year before, but their ride still failed to impress when compared to the ultra-plush cartridge forks found on the Honda CR500R. Photo Credit: Yamaha
For years, many riders had held that liquid cooling was unnecessary on an Open bike, but the eye-opening performance of the new liquid-cooled CR500 and KX500 had most riders rethinking this stance by 1986. Both half-liter beasts pumped out incredible amounts of power and did it with better response and more consistent performance. Unlike an air-cooled machine, the liquid-cooled 500s maintained their performance the entire moto and ran the same on lap fifteen as they did on lap one.
The YZ’s 487cc mill was rather unimpressive down low, before catching fire in the midrange and pulling to a strong top-end surge. Its erratic jetting was its most significant handicap against its liquid-cooled rivals. Its slightly mellower delivery made it popular for off-road use and many less-experienced pilots preferred the YZ’s slower building power to the more abrupt delivery of the CR and KX. Photo Credit: Yamaha
With the YZ490 sticking to air-cooling for 1986, the big Yamaha started with some inherent disadvantages. Most notable of these was its erratic jetting, which hindered throttle response down low and led to a concerning detonation once the motor was hot. Off idle, the YZ felt very rich and reluctant to clean out. This sluggish low-end response made the YZ less explosive when you first twisted the throttle than the arm-stretching Honda and Kawasaki and some less-skilled riders appreciated its less abrupt delivery. Once the YZ cleaned out, it pulled very strongly into a healthy midrange hit and eye-watering top-end surge. Its powerband was highly unorthodox for a 500 single with much less bottom and a longer and stronger pull on top than its rivals.
The new Öhilins designed shock and revamped Mono Cross linkage delivered a much-improved ride for 1986. The shock was well-damped, and the spring rate was in the ballpark for most riders below 200 pounds. The majority of testers rated it as the best rear end in the 1986 500 class. Photo Credit: Yamaha
At its peak, it produced around two horsepower less than the red and green machines, but most riders did not miss the extra ponies. Once the YZ was on the pipe, it was as fast as anything in the class, but its blubbery low-speed jetting made it a bit unpredictable at times. Sometimes, it took a beat or two to clean out before the big Yammer exploded with a massive dose of forward thrust. Its mid-and-up powerband was unique and most riders found it was best to try to keep it in the midrange to avoid the gurgling low-end and hand-numbing vibration on top. If you did hold the throttle on, the YZ pulled well past the point where the Honda and Kawasaki were asking for a shift.
With the right rider, the YZ490 was capable of besting its more advanced rivals. Peak power was a bit lower than the Kawasaki and Honda, but the YZ was fast enough to win. Photo Credit: Dirt Rider
Once the YZ got hot, there was a noticeable drop in power that was not present on its liquid-cooled rivals. For many riders, this was not an issue as the drop in power matched their late moto drop in strength. Jeff Stanton types missed the added power, but most Joe Averages probably counted the power loss as a bonus. Once the 490 was hot it also tended to ping quite a bit, so leaning out the jetting to get rid of the burble was not the best idea. Running race gas and having the head modified were the only real solutions for this rattle and ping problem. Once the head was modified and the jetting was sorted, the YZ490’s motor could be very effective. It was plenty fast for most mortals and the new five-speed was a better fit for the YZ’s mid-and-up powerband. The transmission and clutch were not particularly smooth in their engagement but the broad power of the 490 tended to put less stress on their action than on the higher-strung 125 and 250 YZs. Most tracks could be ridden in two or three gears and riders rarely felt the need to hammer the clutch out of every turn. Keeping big 490 a gear high and smoothly rolling on the throttle was the best way to get it hooked up and keep the big single from rattling out your fillings with vibration.
The Honda CR500R was not for the faint-hearted in 1986. Its forks were fantastic, but it’s pudgy ergos and explosive power delivery could make it feel like a real handful. Photo Credit: Dirt Bike
On the detailing front, the YZ490 was well sorted for the time. The new airbox was easy to service and the lack of a power valve and liquid cooling made working on the top end a snap. There was no radiator to worry about smashing in a fall and the motor was generally very reliable aside from its propensity to ping when hot. As a bonus, the 490 was also the easiest of the Japanese Open classers to start. The kicker did not put your leg at a weird angle, and it was far easier to get lit than the occasionally finicky CR. Jetting the stock 490 was a nearly impossible task. If you leaned it out to stop the gurgle down low, then you ran the risk of running it too lean once it got hot. For most riders, it was best to err on the rich side until you got the head fixed. Without water jackets to dampen the ringing of its fins, the YZ was substantially louder than its rivals and there was no escaping the vibration from that paint bucket-sized piston. That constant vibration also liked to loosen all the YZ’s nuts and bolts so keeping a close eye on everything was a good idea if you wanted to keep the rattling under control.
Gentleman Jim Holley was Yamaha’s top gun on the YZ490 in 1986 racing the updated air hammer to 8th overall in the 500 National championship. Photo Credit: Dirt Bike
Riders praised the new layout and the YZ was comfortable aside from the bend of the stock bars. They received a serious thumbs down for their swept-back shape and butter-soft construction. The grips were also panned for their hard rubber and appetite for chewing palms. The throttle pull for the massive Mikuni was stiffer than some of the YZ’s rivals, but the controls and switchgear were generally comfortable and of good quality. The new decals were handsome, but the mismatched red front numberplate seemed like a rather odd addition to some. The lack of a removable rear subframe made shock servicing more of a pain than on the Honda and if you looped it out and bent things up, it was not as easy as just bolting on a new rear section. The smaller front rotor did not seem to hinder the YZ’s front braking, but the rear drum was notably less powerful than the rear disc found on the KX500.
The 1986 YZ490 was not the fastest, smoothest, or most refined machine in the class, but it offered riders looking for simplicity and versatility a nice alternative to the harder-edged machines in the class. Photo Credit: Yamaha
Overall, the 1986 Yamaha YZ490 turned out to be a surprisingly competitive Open class racer. Despite its relative lack of technology, the big four-nine-oh was more than capable of winning against its more advanced rivals. The air-cooled motor continued to have its limitations, but its chassis, layout, and suspension were much improved. The five-speed transmission helped make the most of its power and finally upped its versatility off-road. Many less experienced pilots preferred the YZ’s mellower delivery to the over-the-top explosive hit and eye-watering acceleration of the CR and KX. Both of those machines were certainly faster than the Yamaha, but very few pilots had the skill, strength, and guts to put all those excess ponies to the track. With a Simmons anti-cav kit in the forks, a bit of head massaging, a rejet, and some race gas, the mighty 490 had what it took to win at any level. Its ringing fins, vibrating motor, and old-fashioned looks were never going to win over the “latest and greatest” crowd, but if you were looking for a fun, reliable, versatile, and easy-to-work-on machine, then the all-new YZ490 was certainly worth a look in 1986.
