1981 Honda RC250M


1981 Honda RC250M

This bike displays the last of the HRC air-cooled motors and the beginning of the single rear shock (pro-link). The bike now sits in Supercross trim with the padded gas tank. Water-cooled motors were available but were often discarded for the air-cooled version to save weight. Many innovations that are used today such as low stiction forks, linkage rear shocks and extended seats, started on this bike.


In 1980, as a direct response to Yamaha’s dominance in professional racing in the mid to late 70’s, Honda formed Honda Racing Corporation. Better known as HRC. When the top Japanese Honda official traveled to the US in 1979 to inform Honda's US racing team of the plan, a memo was passed out to those that attended the secret meeting. Instead of the usual 15 to 20 page booklet outlining the details and strategy for the next years program, this year was different. Each attendee got a one page memo with the words "KILL YAMAHA" in large print. Bob Hannah had to be stopped. There was a lot of screaming and table pounding in that historical meeting, and afterwards, a lot of whiskey was consumed. When the night was over, everyone knew things were different now and this was serious business. The goal was to put Honda on top of the racing world as the absolute undeniable king and anything but number one would be considered failure. The new company (HRC) would be seperately managed and operated but still reside under the parent company Honda Motors in Japan. They started with a 10 year commitment, a huge budget and some very dedicated and talented engineers commited to designing and building the best racing equipment in the world. In the past, Honda had shown flashes of brilliance and built some of the best motocross hardware ever made but they weren’t consistent. At the end of the season a new team of engineers would move in and start fresh, often losing valuable data and momentum from the prior year. The results were sporadic and not acceptable to Honda management. A perfect example of this is when the 1977 RC500M that everyone acknowleged as the best open class bike Honda produced in the late 1970's was followed by the 1978 RC500M, the worst bike Honda produced in the 1970's. This would all change with HRC as it was now one corporation with one mission and the mission would continue from year to year. The focus was so intense that consideration for production feasibility was secondary and essentially out the window. Nothing would be compromised in designing and building the best works race bikes possible. In fact very little was ever shared with the production division. Everything was top secret. Often the already large budget was exceeded and in 1981, the budget of 2.5 million dollars was exceeded by over five times to over 13 million dollars allocated for that year alone!

Factory mechanic Dave Arnold was promoted to team manager and five time world champion Roger DeCoster was hired as a consultant. Together these two would be very instrumental in communicating between what was learned and recorded in racing as well as testing with the HRC engineers that were sent to the US. They also had direct contact with the HRC engineers in Japan. Their only objective was to do everything possible to develop the bikes and win championships.

The HRC works bikes built during this era are the absolute finest motocross bikes ever made at any time. Upon close inspection it is immediately obvious that the people that built these bikes knew and loved what they were doing. Every part fits perfectly, the threads of the machined titanium bolts are cut so accurate that you can thread them all the way in with your hands with no resistance. Even the smallest most unassuming bracket that nobody would ever see is fabricated with precision. The attention to detail in the welding, machining, casting and every other form of fabrication sets these bikes in a class by themselves. They are truly a work of art.

The 1981 RC250M featured here is an early example of the incredible achievements by HRC and was raced by Johnny O’Mara. Since Johnny was Honda’s 125 specialist in the outdoor nationals, this bike was used primarily in supercross races. The bike was also used in the historic 1981 Trophy des Nations race in Lommel Belgium where the US began an unprecedented 13 year winning streak. Its last race was the San Diego supercross. The bike is an engineering marvel and showcase of brilliant craftsmanship.

Starting with the chassis, the frame is constructed from a very high quality chrome moly tubing and hand welded together. The swingarm pivot area uses metal that is machined into shape using very close tolerances on a mill and then welded to the frame tubes. All gussets on the frame that have compound curves are pound into shape with such care that they look like they are stamped pieces. The RC250 also features the first generation of removable sub-frames. This was a huge breakthrough that improved the rear suspension serviceability and also increased the main frame service life. The entire frame body is a very compact and solid unit that had advantages that could immediately be felt on the race track.

New technology was also applied to the front forks. This was the second generation of cartridge front forks that featured adjustable rebound and compression damping. The fork tube diameter was increased to the now standard 43mm and the chrome tubes themselves featured a very expensive chroming process that was designed to reduce stiction. These tubes were housed in a set of billet magnesium fork sliders on the bottom and held into a set of forged triple clamps on top. The top triple clamp has provisions for adjustable handlebar mounts so the ergonomics could be adjusted for each rider.

The rear swingarm is tapered in shape providing the best shape and design for strength and stress distribution. The front section is a complete billet piece from the swingarm pivot back to where the linkage mounts then the side forks are made from sheet aluminum using beautiful compound bends that show no tooling or hammer marks whatsoever. This is then beautifully heli-arced to the front billet section as well as the tapered rear axle blocks, all designed to be a swingarm for a 1981 RC250M. The cost of one swingarm alone was astronomical. Attached to the swingarm is another tool room special, the rear chain guide. With its Teflon chain-block and nylon roller held together with special billet titanium bolts, the chain guide is another example of HRC taking a simple part and creating a masterpiece.

The rear shock is a works Showa special with a billet aluminum detached reservoir and provided excellent rear suspension for the early Pro-Link works bike. The links themselves are machined from billet steel and aluminum and were coated to resist corrosion. Different links were tried in this early stage of rising rate linkage rear suspension. Rear wheel travel had evolved to around 315mm at this point and the shock stroke during this period was aproximately 110mm.

 

The profile of the padded supercross tank was a first that was developed by HRC and really improved rider position in the corners. Notice the weld quality on the frame.

The front and rear wheels feature hubs that are machined from billet magnesium. This was a departure from the traditional sand-casting practices that were common for wheel hubs at the time. The front and rear backing plates though remained sand-cast. Also new was the nikasil brake liners that were fused onto the magnesium hub instead of iron pressed in liners. The 1981 RC utilizes the first generation of double leading shoe front brakes and with the special compound brake shoes, provided braking power not seen on a motocross bike before.

The main frame of the chassis was also a work of art. Keeping very tight tollerences around the engine to ultimately connect the pivot and linkage mounts areas to the headpipe area tubes formed together with well thought and asthetically pleasing formed gussets. As trick and well thought out as the chassis is, it is the HRC motor that really stands out. The very small crankcases are sand-cast in magnesium using a very high quality controlled casting process. All crankshaft and transmission bearing bores are strengthened with brass sleeves to eliminate bearings becoming loose in the soft magnesium bores. The casting is nowhere near as porous as on other brand works bikes. Each case is then treated with an anti corrosive substance. The cases are then matched and numbered as a set. If you need to replace one crankcase half, then you replace the set.

Inside the cases is where things start pushing the envelope. After endless hours of research and development by some very smart engineers, HRC came up with a crankshaft that was lightweight, strong, provided maximum crankcase pressure and the amount of inertia produced was easily adjustable. The crank wheels started out of billet and then were machined hollow. They were then electro laser welded together to provide full circle flywheels. The inertia could be adjusted by installing different weights that were held in by cir-clips and these weights were made from nylon, steel and tungsten. You could actually adjust the inertia of the crankshaft to alter the desired power-band. Connecting rods were made from billet and highly polished. The total package was a very strong flex free crankshaft. The crankshaft was so strong that in testing against a comparable crankshaft made in the conventional manner, the HRC crankshaft added measurable horsepower throughout the range on a 250. Not only did they add power but vibration was almost non existent adding to less rider fatigue.

The gearbox is also an engineering marvel. The gears themselves are all hand machined out of the highest grade material possible and then tumbled in a special media to provide greatly reduced friction when rotating on the gear shafts. Several different materials were tried for the shift drum such as aluminum and titanium but a very milled out swiss cheesed chrome moly design was selected because of its strength and lower stiction properties. Also a very milled out swiss cheese design clutch basket and primary gear made from one piece steel provided a durable and very lightweight positive clutch. The entire drive train was very strong and friction was greatly reduced adding to an incredible performing motor.

Different cylinders were available with different porting and they were available in both air and water-cooled versions. At the beginning of 81 and especially for sx racing where maneuverability was even a higher priority the air-cooled versions were preferred to the water-cooled mainly because of the high center of gravity  weight feeling due to the high placement of the radiators and slightly additional overall machine weight plus the wider gas tank and radiator shroud impacted rider ergonomics at that time. The team worked all year on repositioning radiators more low and narrow and exhaust pipe shape and routing and by the end of the season were well on their way to producing a water-cooled 250 with a narrow ride position and low center of gravity. Originally the cylinders were chrome plated which would slightly flake around the porting areas over time. Spare cylinders were rare and hard to come by. After the Trophy des Nations race in Lommel Belgium, team manager Dave Arnold learned of a nikasil process that was being performed in Germany. Before returning to the states, Dave took all seven works cylinders to a small shop in Stutgart Germany and had the cylinders resurfaced with the nikasil process. The results were overwhelming in favor of nikasil over chrome as the performance and reliability were greatly increased. This led to HRC using nikasil on all subsequent works cylinders and shortly after the same process was transferred to the production bikes.

Different exhaust pipes were available for different track conditions and desired powerbands and even some special cone pipes were produced in-house. The development process never stopped throughout the season. This was also true for chassis geometry and linkage ratios and suspension settings / multiple settings were tried throughout the season.

One concept that HRC worked very hard at was improving the ergonomics of the motorcycle. They made the bikes so the riders could adjust key components to suit their own riding style. One breakthrough came with the supercross tank with the padded top. This gave the rider much more flexibility in moving around for weight transfer. The foam pad contoured nicely with the seat and was an excellent first effort. This was only available on the supercross tank because it negatively impacted gas capacity not acceptable on outdoor tracks. The outdoor tank held much more gas therefore there was no pad.

The fasteners and brackets themselves are a work of art. All of the fasteners and hardware on the RC250 were designed and made individually for a special purpose and every single part is made at the highest standard. Most of the fasteners are either titanium or aluminum and steel was used occasionally in very high stressed areas.

HRC was in their second year when this bike was built and it is obvious that an enormous commitment was now underway. Every challenge was met at the highest level and while not every innovation worked, the relentless pursuit of perfection is evident. The result of the HRC effort is the longest and most dominant dynasty in motocross that began with this early effort.

 

The HRC engineers broke ground with this bike, and many of their innovations are still in use today.


1981 Honda RC250M Photos


Johnny O ‘Mara’s comments:

When I first got hired to be a factory Honda rider I was just glad to be there. I was approached by Yamaha around that time too but for me it was a no-brainer to sign with Honda. In 1980 when I was on the Mugen team, Honda always made a spot for us at the races and I knew the guys there real well. I also saw the commitment they had there. It was my first season riding the full works bikes. When you are riding for the factory Honda team you are never lacking in the bike department. The RC250 that year was a full works HRC bike built in Japan.

I was hired to primarily ride the 125 class in the nationals but I rode this 250 in supercross races and the des Nations at Lommel Belgium. It was my first time riding the bigger bikes and to do it on a full works bike was a dream come true. We set our bikes up to fit us individually and if we needed anything at all, it was there with in a day. The organization was second to none, from the personal to the management everything was first class. I wasn’t as picky on setting up my 250 as I was my 125 but the bike was set up very well.

Riding the bike gave me a lot of confidence in myself. It just did everything very well. I did do some testing with the 250 but much more on the 125. The factory Showa suspension on both bikes was excellent. They had the best internals and this special finish on the chrome stantions and that is one of the reasons the forks were so smooth. The works Showa shock was very good too. Showa always had the best suspension.

We did set the bikes up differently for different tracks. Many of the basic settings were already decided for us as to what combination to run and then we would fine tune it from there. For example at a supercross I would run an engine set-up that might not be the biggest on top end but at an outdoor event like at the des Nations we had the bike set-up for more top end and a broad power band because of the deep sand. My bike was running real fast that day and I holeshot both motos.

Another neat feature Honda had was the seat foam on the supercross tank. That was a real breakthrough and I think we were the first to do that. It really helped and gave me the ability to get up there and used that area for the corners. It also allowed me to get way up on the tank for the starts, it was very functional. That tank is the first thing that comes to mind when I think of this bike.

I was really fortunate to be able to ride on the factory Honda team I spent about 70% of my time there was the highlight of my career. To be on the Honda team was everyone’s dream and I think it is that way even today. They did everything they could to help you win. The team was focused and everybody worked together. Winning the des Nations in 1981 really capped off my first year at Honda.


Detail Photos



Historical Photos


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