1976 Yamaha OW27
1976 125 National Champion
1976 Yamaha OW27
Every once in a while in sporting events, there comes along an unprecedented event and absolutely nobody sees it coming. All the stars line up perfectly and the unbelievable happens. After it happens, it is so overwhelming it becomes folklore almost immediately, a historic event that lives on for the ages. In Major League Baseball it could be the “shot heard round the world.” In the NFL there was “the catch.” made by the famous Joe Montana pass. These events become legend.
On April 4th 1976 at the opening round of the AMA 125 Nationals near Sacramento California, such an event took place at the Hangtown national. A rookie factory Yamaha rider named Bob Hannah who had only been racing for a year and a half, total, defeated the 2 time 125 National Champion Marty Smith in a race that can only be described as phenomenal. There wasn’t a person on the planet that thought it could be done including Bob Hannah himself. “I never thought I could beat him that day,” recalled Bob years later. “Nobody could beat Marty at that time, he was invincible”. What was so amazing about that race was that Bob Hannah came from last place in the first moto and in nine of the most amazing laps in 125 history, took in the lead and won the race. 125 pro Kim Blackseth remembers the day well. “I was at the side of the track and through this section of 3 foot whoops with tree roots sticking out everywhere, Hannah came through there with the bike swapping back and forth, wide open! And that was just practice.” The second moto was nearly the same although Marty’s bike did break near the end. Hannah literally owned the track and decimated the competition. Over 40,000 fans left the track that day stunned and some hard-core Marty Smith fans who made the eight-hour trek to see their hero smoke em’ drove back home in utter silence. Over thirty years later and many fans who were there that day still say it was the best race they had ever seen.
The bike Bob was riding that day was almost as amazing as Bob’s historic win. It was the first ever water-cooled motocross bike. Nothing like it had been seen or even thought of before. After it was all over and Bob went 1-1 for the overall, the Yamaha pits were crowded with people wanting to see this new exotic 125 works bike and who was riding it as most people had never heard the name Bob Hannah. Marty’s mechanic Dave Arnold summed up the day. Bob who? And his water-cooled what? Running us down in both motos?
Billy Grossi (far right) had the best seat in the house at Hangtown as Bob Hannah went from dead last to win the first moto in one of the most amazing come from behind rides in motocross history defeating the undefeatable Marty Smith. The crowd of 40,000 was absolutely stunned. To this day, many that witnessed the race say it was the best race they ever saw. Photo by FTE
Over the next few months, the OW27 would draw unprecedented attention, as it was the subject of numerous articles in the major motorcycle magazines. Speculation ran wild as to how and why the coolant went from the radiator into the frame, down into the cases and then came back up through the steering stem. Some of the theories as to the advantages and disadvantages were, that you can go down several sizes on jetting due to the bike being water-cooled and gain more power. There were those that thought the radiator hoses would get snagged and come loose during competition and it would prove unreliable and never make it's way into production. It would just be a fad that would come and go. Most people though, realized that Yamaha was on to something and that this bike was for real. Motocross bikes were in a hyper-evolution stage in suspension and chassis design during this time as just 4 years earlier, the standard motocross bike had about 7 inches of travel up front and 4 inches in the rear. Things had come a long way and were changing fast but nobody saw the water-cooling coming. The bike itself would actually send the 125 national championship series that year into turmoil during the second round at Buchanan Michigan, when privateer and former factory Honda rider Mickey Boone tried to claim it.
The OW27 was far ahead of it’s time, in-fact, even though the water-cooling provided Yamaha a clear advantage, it was pulled from the US factory team because of fear of losing a bike to the claiming rule that was used twice (unsuccessfully) in 1976 and would not resurface again until 1980. The advantage of water-cooling a high power, small displacement two-stroke engine is huge, especially when the moto’s were forty minutes plus two laps. A highly modified 125 could easily lose thirty percent of its power at the end of a forty-minute moto, but the water-cooled engine would maintain nearly the same power throughout the same time frame.
A special cylinder and head were cast that had connecting coolant passages that was supplied with a radiator mounted on the triple clamps. The cylinder and head still maintained marginal cooling fins that were supposed to give the bike an extra lap or two in case of a coolant failure. To get the coolant from the radiator to the top end required some real clever routing as to not pinch the hoses while turning the bike. The coolant started in the radiator and was routed through the bottom triple clamp, in through the steering stem and out through the frame and down into the crank driven water-pump on the clutch cover. The coolant then went into the back of the cylinder head, through the cylinder; back out through the front of the head into the steering head, up through the triple clamp and into the radiator. The steering stem had a seal at the mid-point that separated the supply and return. The design was somewhat complicated but allowed unobstructed movement of the handlebars. The total length of time for the coolant to circulate through the system was just a few seconds. It was very important to bleed the air out of the system with the bleed screw on the left side of the cylinder. This had to be done during warm up otherwise a seizure would result.
The result was a very reliable 125 that would not lose nearly the power that an air-cooled bike of equal tuning would. The water-cooling allowed for more aggressive port timing and leaner jetting without sacrificing reliability. The OW27 was light years faster than the prior year’s works 125. When Yamaha pulled the water-cooled motor and ran the 1975 works engine due to a claiming rule scare, Hannah complained that the air-cooled bike was nowhere near as fast as the water-cooled engine and that his chances at the championship would be compromised. Water-cooling was definitely a huge advantage especially in the 125 class where the bikes are nearly full throttle all the time.
Yamaha applied equal attention to the chassis and suspension components as suspension travel was increasing and this required newly designed frames. The OW27 frame was designed to accommodate a full 10 inches of travel at each end and was constructed out of very light chrome moly tubing.
A common problem with early long travel bikes was rear suspension fade. As suspension travel increased, so did the demand of the shocks. The oil would break down, lose viscosity and eventually the shock damping would be lost. To compensate for the loss of oil viscosity, Yamaha designed the OW27 shock with a thermostatically controlled valving system that would actually adjust, as the oil got hot. The theory was to maintain the same relative valving passages at all times regardless of oil viscosity. This was very expensive to do and the shocks were reportedly $5000.00 a copy. Compare that with the cost of a standard 1976 production 125 at just over $900.00. Also, realizing the need for a progressive spring rate, Yamaha used a combination of a light spring for the small bumps inside of a larger spring. This was originally developed in Europe with 1973 250 World Champion Hakan Andersson. Hannah’s mechanic Bill Buchka was in constant contact with Yamaha’s European works team and based much of Bob’s set-up on what was learned on the GP circuit in Europe. Bill also did a fabulous job maintaining the bike throughout the 125 national series.
For the front suspension, Yamaha again started with a clean sheet of paper and a set of handmade Kayaba forks with 10 inches of travel designed just for this bike were used. For 1976 Yamaha adapted an off-set front axle and along with better turning capabilities, this allowed the fork tubes to extend below the axle for longer travel. Since the bike was at the minimum weight limit of 176 lbs, the diameter of the tubes themselves remained a very spindly 34mm but the tubes were knurled for better grip at the triple clamps. The front and rear suspension were designed to complement each other and except for a shock failure at the third round of the 125 nationals in Midland Michigan, they performed excellent and were well balanced with the chassis. This coupled with the OW27’s lightweight made for an excellent handling machine that raised the bar and seemed to complement Hannah’s agressive riding style.
Dave Arnold, Bill Buchka and Terry Good documented the entire 1976 125 national championship series race by race. Click the above History tab, then go to MX History. Since 2008 we have had over one million hits on that article.
1976 Yamaha OW27 Photos
Bob Hannah's comments:
The bike was kind of like me, It wasn't the fastest but it just stayed there. I might not have been the fastest rider with the fastest lap times every week, but I could run the same lap time every lap for 40 minutes. The bike was the same. The factory Honda's could out run it, but the OW27 went the whole race at the same speed.
After Mickey Boone filed a claim on my bike, we went to the prior years works air-cooled motor in the 1976 works frame and it was slow. I remember Steve Wise's production bike was faster than mine at Keysers Ridge. With the water-cooled motor, it kept going, same tone and same power all the time. After a couple of races with the old air-cooled motor, I said toYamaha, "If you guys want to win this thing, you better give me the water-cooled bike, otherwise, we're going to get beat every week". They gave the OK and from then on, I rode the full works OW27.
As far as geometry and suspension, I was just a kid at the time and didn't really know much about testing. I pretty much just rode what you put under me. Bill Buchka would set it up and I just rode it. We would try different things and I would say, "yeah that works better", but I didn't have the experience to develop a bike back then. Marty Smith was probably better than me at that point- as far as testing goes-because he had a lot more experience than me. That might have hurt him in 1976 because he might have thought about it too much. They were always on a different bike that year. As a rider, if you think like, "His bike is better than mine", it drives you crazy and that's not good. For me, I had nothing in my head, I had no pre-conceived anything. I just rode the bike. Fortunately we had a great bike.
Soaring through the trees in perfect form at the Mid-Ohio 125 USGP. In 1976 Hannah made very few mistakes as he dominated the 125 national championship series. Of his seven AMA championships, the 1976 125 title is his favorite.
Bob Hannah, was the number two rider of Yamaha's 1976 two man 125 works team. Bob's teammate Danny Turner was the top privateer on the 125's for 1975 and there was some positive speculation as to how Turner would do on this new bike. Bob was just glad to be on the team and along with everybody else, never thought he had a chance to win. Top five, maybe, but win....Never! Here, Hannah full gas through the Mid-Ohio whoops on the super exotic OW27. Hannah was nearly unstoppable. Charley Morey Photo.
Bill Buchka's comments:
We got the new works OW27 about four weeks prior to Hangtown. Bob and I had two bikes and our teammate Danny Turner and his mechanic Ed Schiedler also received two bikes.
The Yamaha water cooled concept used on the 1976 OW27 was new to the US championship but had actually been raced, albeit in a much different configuration, in the 1975 Japanese 125cc championship, so it was not a total unknown quantity to us within the YamahaTeam.
Prior to the start of the 1976 US championship, we tested the bikes at every type of available track that offered terrain similar to the tracks that would be on the 125cc national circuit. We went to Saddleback and Carlsbad for hard pack. Hangtown was a sand track so to prepare for that we tested at Santa Maria and we even tested in the desert. We tested in as many circumstances as we could in the limited time that we had. We started with the basic set-up as the bikes came from Japan and tried to narrow it down from there. We relied on information that we received from Japan and our own structured testing program. We spent a lot of time testing internal and external gear ratios, suspension settings, carburetors, jetting, and reliability limits, all in a very short period of time. Through my own personal contacts, we even turned to our Yamaha teammates in Europe to gain as much information as we possibly could to help us win the US 125cc championship.
The OW 27 was a revolutionary bike in as much as it introduced the concept of water cooling into a level of professional racing previously unseen in any other motocross championship with a profile as high as the US championship. At the time, they were produced in such small quantities that each one was somewhat different from the other, requiring that we tailored individual components to individual bikes. In other words, a particular component on one bike might require considerable modification to fit on a seemingly identical bike. They were all truly hand built, and required an equal amount of detailed attention in the field, as we pursued the US championship.
During the 1976 championship, the fact that someone actually utilized the AMA "Claiming Rule" to try and obtain the OW27 turned the technical aspect of the championship on its ear. All the major factory teams took different approaches as to how to protect themselves from the potential loss of a most valuable commodity, their intellectual property.
After the 1976 Mid-Ohio 125cc USGP, Bob told Yamaha‚ I feel so much better with this bike than with the air cooled set-up we used at the last two nationals. I have to have this bike if you want me to win this championship. I supported the request 100%. If we were going to win this thing, we had to have the best equipment available to us. Even with the risk of the "Claiming Rule." By this stage in time, Bob commanded a lot of respect with the Yamaha factory and I don't think they had much of a choice. We got the final approval from Yamaha management both in the U.S.and Japan. From then on we campaigned the water cooled OW27 works bike for the remainder of the 1976 125cc championship.
Obviously, this is much more than just a simple motocross bike. It is a truly innovative motocross bike that represents an engineering and competitive milestone in the history of motocross.
Terry Good's comments:
The 1976 OW27 is one of my favorite bikes of all time. There are other bikes that may have a higher pedigree for sure but this one was from the era I raced in as a pro and I was fortunate to enough to compete in the same series and see it on a weekly basis. I had been to most of the CMC races in 1975 when Bob was riding for Suzuki as a test rider and I knew how hard it was to compete at tracks like Saddleback and Carlsbad at the local level because there were so many real fast guys that had those tracks wired. The local CMC scene in southern California at that time was part of the southern California culture. You could race four to five days a week every week and many of the top guys did just that. On top of it all, you had the factories headquartered there and there was what seemed like a dozen speed shops (DG, FMF etc.) and all had sponsored teams that would compete in these races. To beat these guys in their own backyard seemed nearly impossible. With less that a years total racing experience, Bob Hannah was dominating the pro class at these races. I never saw him get second, he won every one of them that I saw and it was the 250 and 500 class in the same day. Amazing! I did hear that his first time on the 125 Suzuki he got third and he had two DNF's in the bigger classes but he won every other moto. Now, fast forward to Hangtown in 1976.
While back east preparing for the 125 Nationals I got a phone call from my CMC friend Kim Blackseth who was at Hangtown. I remember the phone call like it was yesterday. His voice had panic all over it. "Terry, your not going to believe who won......Bob Hannah!!! He's on this works Yamaha that is water-cooled with water pumps on it, you won't believe that bike". First of all, I had no idea that Bob was even riding for Yamaha at the time and the thought of anybody beating Marty Smith was almost unimaginable. For seven long weeks to the 2nd round at Red Bud in Buchanan Michigan, I waited to see this bike. On the way to the race that is all Kim and I talked about and when we got there, the first thing I did was look for the Yamaha truck in the pits. Upon seeing it for the first time from a static point of view, the bike was way over the top. It was beyond trick, nothing like this had been even conceived before. It was the buzz of the pits that day and everybody was talking about it. It was also just as impressive on the track and to me it completely complimented Bob's aggressive riding style. It looked very well balanced and forgiving and it was obvious that the chassis design was aimed at longer travel than what was the norm at the time.
I didn't compete that day due to the AMA not bringing my license to the race so I got to watch one of the best races I've ever seen. When Hannah went to the line for the first moto on that bike, I remember thinking, boy, "is the world in trouble now." He and Marty Smith had the mother of all battles in the second moto with Bob coming out on top. Every single race after that I always made my way over to the Yamaha pits to check the bike out and the impression it made on me is something I'll never forget. I have to say, I may have been the only one including Bob who believed he would win the title right from the get-go because of how good he did in the CMC races the year before. The bike and Bob did meet their match though when Honda unveiled the all new RC125M Type II at Delta Ohio. That bike was incredible and Marty rode it flawlessly, but that story is for another day. Stay tuned.
Midway through the season at Delta Ohio, Honda debuted the 125 RC125M Type II. The all new bike was on par with the OW27 but after nearly losing the bike in a claim filed by a privateer at Delta, Honda management sent the bike to the back of the truck for the next round in San Antonio. Here at Delta Marty chats with Suzuki's Danny LaPorte mounted on the factory Suzuki RA76. MXworksbike's Terry Good is on the far right on a highly modified DG Yamaha. Note the loose side panel on Marty's bike. Werner Strube Photo.
- This motor was the talk of the motocross world in 1976 and rumors ran wild. The combination of water jackets and cooling fins had most confused. Some magazines actually reported that the top end was air-cooled and it was the lower end that was water-cooled. The fact is that just the top end is water-cooled and the fins are there as some sort of a safety net. The center cases are die-cast and very similar to stock except the cylinder stud spacing is wider to accommodate for the much larger transfer ports for more mid-range power. The OW27 wasn't the fastest in top speed but it made very good power and maintained it for the 40 minute plus two lap motos. This was a huge advantage in 1976 where many 125's made incredible power but only for a short time. It wasn't uncommon for a 125 to lose over 20% of it's power during the long 40 minute motos. The gear box has the same ratio's as the YZ 125X, only they are hand cut and drilled for lightness. Yamaha did experiment with a water-cooled works 125 in late 1975 but that was near the end of the Japanese Nationals and it never saw action outside of Japan.
- Take a look at the close up of the sand cast cylinder and head. The bleed hole at the bottom of the cylinder served two purposes. First to drain the cylinder for servicing and second, it was mandatory to loosen the bolt after running the bike at warm up to remove any air that might be in the system. If you didn't do this, an almost certain a vapor lock would occur that would guarantee a seizure. You can see the original safety wire still on the bleed bolt that was wired up by Bill Buchka back in 1976. Below is a close up of the sand cast magnesium clutch cover that contains the water pump impeller.
- As with most works bikes, the center cases are matched by hand at the factory and numbered. The kick start lever is made from billet machined steel with the foot rest turned on a lathe and welded into the lever. The kick start shaft is smaller in diameter than stock and uses a different spline pattern.
- The motor is attached to the frame by machined aluminum motor mounts and to do so at the bottom rear, a special spacer was made. Notice in the photo below, there is a steel sleeve pressed into the spacer. This insured that the soft aluminum wouldn't cause the bolt to come loose and save weight at the same time. This is just one small reason why works bikes cost so much money.
- The carburetor is a 34mm mikuni that is hand bored to the exact spec and in the bottom photo you can see OW27 stamped right under the choke lever. The reed cage is larger than stock.
- The exhaust pipe is made from hydro-form, cone and stamped sections. Different pipes providing different powerbands were available. The silencer, although it looks very similar to the stock silencer, is actually very different and like the pipe, there were different ones to choose from. Bruce Hollingshead did a fantastic job saving the original as it was in pretty bad shape.
- The forks are completely hand made by Kayaba and the lower sliders are carved from billet. The front suspension provided excellent performance and worked very well with the chassis design. At the triple clamp contact points, the fork tubes are knurled for a better grip and they are turned down on a lathe between the upper and lower clamps for less weight. The complete fork assembly is very light. It was reported that one set of OW27 forks cost more than three YZ125's. The front brake arm at the backing plate is made from drilled steel for more positive braking. In the second photo below you can see how the return coolant hose attaches to the steering head.
- The front wheel is the typical works Yamaha design that was used from the early 70's with a magnesium hub laced to a DID rim. These set the standard at the time for braking power and light weight. The same basic design was carried all the way into the early 80's. Notice the beautiful machine work on the aluminum slider in the photo below. Fans lined the fences just to look at the bikes that carried these parts. Two photos down you can see how Bill Buchka made sure the brake cable stayed out of the tire. He used white tape that would be wrapped around the dust wiper twice, then the cable was put in place and then wrap it around several more times. He always made sure that each time he wrapped the tape around, it was wrapped exactly over the previous tape to insure a very neat look. Bill was very meticulous about his bikes.
- The rear hub is an extremely light weight conical design that is sand cast in magnesium. The backing plate is a die cast magnesium stock unit and together with the rear hub provide a very light weight rear wheel. All the un-sprung weight on this bike is kept to an absolute minimum. The tires on the bike are Trelleborgs. Bill had much experience with Pierre Karsmakers and the other European factory Yamaha riders and it was from their influence that Bill selected Trelleborgs much of the time for Bob.
- The rear shock is completely handmade by Yamaha. It uses 2 springs for progression and also features a thermostat inside the shock that adjusts (closes) the damping as the oil gets hot and loses viscosity. This was experimental and initially didn't work as well as hoped. At Midland Michigan, Bob had troubles with the rear shock in the second moto when the shock failed and lost all damping. When it worked, it worked great. The cost in 1976 dollars for one shock was around $5000.00. Compare that to the cost of a complete 1976 YZ125 motorcycle at around $900.00.
- Most of the bolts that aren't titanium are machined steel as you can see by the drilled steel bolt on the torque arm above and the footpeg bolt below. Only some of the small 6mm steel bolts are standard. Below, Bill wrapped the brake pedal with a piece of rubber as a stop where it met the clutch cover. Space and weight were saved with the way the rear brake pedal is mounted by actually sliding over the kick start shaft. There is a brass bushing pressed into the pedal that is dimpled for grease to set in and provide a very well thought out set-up. The rear brake pedal has a very solid feel to it that you only get on a works bike.
- Bob used a Magura front brake set-up exclusively in 1976. These were the same as what was on his Husky before he was a factory Yamaha rider less than a year earlier. Below is a set of works air-caps that Bob did not use on this bike as well as the machined top triple clamp. Bob used a cast top clamp, the machined lower clamp that you see below and standard fork caps with no air. The pinch bolts are billet titanium.
- The gas tank is made from very thin but very strong aircraft quality aluminum and is by far the lightest gas tank I have ever seen. Below the side panels are made from a translucent polypropylene plastic. In 1976 pro riders were ranked and you were either an expert pro (ranked) or a novice pro (unranked). Expert pro's used white number plate back grounds and novice pros used black number plate back grounds. Bob was novice pro in 1976 as it was his first full year and Bill pop-riveted black Cal-Custom plastic number plates to the works side panels. As a pre-caution, he used Japanese brown duct tape to keep the side panel to the frame.
- At the top of the steering stem, is a fitting that the coolant passes through to return to the radiator. The mix was 70% distilled water and 30% antifreeze.
The most famous number plate ever to grace a 125 motocross bike. Bob's all original number 39 as it sits today.
Bob Hannah and Bill Buchka pose with the only remaining bike of the two OW27's Bob used in 1976. Serial numbers recorded by Bill on the race reports confirm. Photo by Fran Kuhn.