GP’s Classic Steel #12 : 1982 Yamaha YZ250
By:
swizcore

This week’s selection from Greg Primm’s Classic Steel is Yamaha’s first liquid cooled 250cc motocrosser, the 1982 YZ250J.

By: Tony Blazier

The 1982 YZ250J was a radical departure from all of Yamaha’s previous 250’s. Everything from the up-the-tank safety seat to the small looking liquid cooled cylinder told you this was no rehashed 70’s machine.

For 1982 Yamaha introduced an all-new YZ250 for the first time in several years. The YZ250J was a complete redesign and featured the very latest in motocross technology. This was the first year for Yamaha’s highly touted “Yamaha Power Valve System” and liquid cooling on the YZ250. In the chassis department, the ’82 YZ featured an all-new frame and radically revised rear suspension system. Even the plastic and graphics were all new for ’82. On paper the new YZ looked like a world beater. In reality, it was a colossal disappointment.

The ’82 YZ line saw the introduction of Yamaha’s all-new variable exhaust port system. The Yamaha Power Valve System or “YPVS” promised the torque of a big bore and the rev of a 125, all from the same motor.

The YZ250 motor was at the very cutting edge of two-stroke technology in ’82. Yamaha had been using prototype versions of their power valve system for years on their OW factory racers to great effect. For 1982, Yamaha brought this works technology to the masses with their new YZ125 and YZ250. The Yamaha Power Valve System, or “YPVS” used a small rotating drum above the exhaust port to alter port timing based on engine RPM. This allowed the engineers to tune the motor for a broader spread of power, much like the variable valve timing systems on a modern car. Complementing the YPVS was Yamaha’s controversial liquid cooling system. Believe it or not, there was a time when people actually thought it was a waste to use liquid cooling on a 250. They thought the added complexity and weight of a liquid cooling system outweighed its small benefit in sustained power over time. With systems like the one on the ’82 YZ, it is no wonder people were not yet sold on the concept.

It would take a few years for Yamaha to make full use of the potential in their YPVS motor design. The ’82 YZ power plant had a torquey low-end, but little else. The flat, listless motor was last in the field in ’82.

For all its techno trickery, the ’82 YZ250 was actually back of the pack in performance. The YPVS motor did indeed have the excellent low-end power expected with the new power-valve system. It was after this low-end surge that the new tech YZ fell apart. In theory, the YPVS should have allowed the YZ to have a wider powerband than it competition. In reality, the ’82 YZ motor turned out to be a one trick pony. Once the motor got past the low-end, it just fell on its face. The mid-range was flat and the top-end was non-existent. The ultra modern YZ power plant actually ended up getting smoked  by Kawasaki’s decidedly old school, air-cooled KX250 motor. Technology like power valves were indeed the future, but Yamaha’s first attempt did little to show its potential.

The YZ’s radiator was mounted behind the front numberplate, attached to the upper and lower triple clamps. This made the steering of the bike feel decidedly heavy and unresponsive.

The unorthodox radiator location required that coolant be piped down through the frame to the motor. This led to chronic leaks, as the many hoses and clamps were stretched and pulled by the constantly moving steering head.

The liquid cooling system on the new YZ had its own set of issues. At this point the manufactures had yet to figure out the best place to mount the radiator on a bike, so each one took a different approach. Yamaha’s had been to mount their radiator up high behind the front number plate. This caused a couple of problems. The first issue was complexity, as Yamaha had to figure out a way to get the coolant from the radiator to the motor while still allowing the rider to steer the bike. Their solution was to run the coolant hose inside the steering stem and then down the frame. Unfortunately,this rather complicated system led to leaks that would never quite go away. The other issue with the Yamaha’s set up was that it negatively affected handling. Placing the radiator and all its hardware on the triple clamps meant that there was a lot of weight very high up on the chassis. This made the steering of the bike feel sluggish and added to a very top-heavy feel that no one liked. The system was so poorly designed that Yamaha’s factory team in ’82 actually went back to air-cooled motors on their race bikes. 

The Hurricane absolutely hated these early eighties YZ’s.  He refused to ride the top-heavy, ill- handling machines, and actually went back to an air-cooled motor on his factory racer in ’82.  Bob became so fed up with Yamaha’s run of subpar machines that he left the company to seek his fortunes with Team Honda at the end of the ’82 season.

The chassis on the ’82 YZ250 featured Yamaha’s first major redesign of their Mono-X rear suspension system since its introduction in the mid seventies. In an attempt to keep up with Suzuki’s class leading Full-Floater suspension, Yamaha had ditched their original monoshock design and come up with their own version of a rising-rate linkage. The new Mono-X was kind of a hybrid system between their old school monoshock and a new school linkage set up. The shock was still mounted up high under the seat like a seventies mono, but it was now connected to a set of linkage arms instead of a big triangular swingarm. It was a halfhearted effort that provided neither the superior performance of the Suzuki system or the simplicity of their previous design. Up front the YZ faired a little better with a set of massive (for the time) 43mm Kayaba forks. They provided decent damping performance but were too softly sprung and prone to bottoming over any decent size jump.

These forks were state of the art in ’82. The Kayaba front forks were considered massive at 43mm in diameter and offered very little tune-ability. Compression and rebound damping were fixed, with no external adjustment available. Adding or subtracting air pressure was the only way to fine tune performance without disassembling the units.

Here is a good look at the ’82 YZ’s new Mono-X rear linkage. The new rear end retained the previous design’s shock location, but now it attached to a rising rate set of linkage arms. The ‘82 design suffered from a high center of gravity and mediocre performance. For ’83 Yamaha would ditch this design altogether and go with a setup much closer to what we use today.

The handling of the YZ was badly compromised by the choices Yamaha had made in the design of the machine. The bike was seriously overweight, tipping the scales at over 240lbs. That is 15lbs more than a 2012 CRF450R four-stroke and 22lbs more than the ’81 YZ250 it replaced. Even worse for the YZ, all that weight was way up high on the bike where you felt it the most. The high center of gravity and porky weight made the bike feel ponderous on the track. The overly soft suspension and slow motor only added to the sluggish performance.

Dual leading shoe brakes like this one were as good as the drum was ever going to get. They were far superior to the single leading shoe brakes of the seventies, but a far cry from the discs we use today. Even a dual leading shoe brake like this would require the use of all four fingers to bring a bike down from speed. Amazingly, Dirt Bike commented that they did not know how anyone could need more brake than this in ’82. Now this brake would feel underpowered on a 50cc minibike. My how times change.

The ’82 YZ250 was an excellent example of lots of potential but no polish. The bike felt like a half finished design that still needed all the kinks worked out. It was a slow, overweight, needlessly complicated and generally lackluster effort that pretty much summed up Yamaha in the early 80’s.

The groundbreaking ’82 YZ250 ended up being a major disappointment for Yamaha. It was a design with a huge amount of potential, but the end product was poorly executed. This was pretty indicative of Yamaha in the early eighties. They were always looking for the next acronym or gizmo to throw on their bikes, but they just could not get the basics nailed. The ’82 YZ250 turned out to be an excellent technical exercise, but little else. In a sport where winning is everything, that was nowhere near enough.

Comments

82 YZ250

Very cool! Nice write up man. I think it's cool to see the development of bikes from what to me isn't that long ago. Thanks.