1979 Yamaha OW40


1979 AMA 250 National & Supercross Champion

In 1979 two things were very clear in professional motocross. Bob Hannah was the best motocross racer in the US and the Yamaha OW40 was the best 250 motocross bike that year. Ask anyone.

Hannah had just come off of an unbelievable season in 1978 by decimating the competition in the 250 supercross and 250 nationals. He went on an unprecedented run of winning 22 motos in a row and was shattering records on a weekly basis. Bob’s wins were so decisive that many of the motos were won by over a minute and at the opening round, he nearly lapped the field. The bike he was using was the all new OW38 works 250 Yamaha. This bike was lightweight, well balanced and sported a motor that made very good mid-range power. After the problems the Yamaha team was having with the 1977 works bikes, the Yamaha engineers rolled up their sleeves and for 1978 produced a 125, 250 and open works bike that had all the other factory teams playing defense. The bikes were state of the art in everyway.

As the suspension travel was increasing so was the flex in the chassis of a conventional twin-shock bike. Yamaha with the monoshock completely avoided this issue because of the triangular swingarm that provided a stiff chassis and allowed the bike to track much better in the rough than the competition. As an illustration to the stark contrast in chassis performance, one of the Honda team managers recorded a team rider’s response in his notes at a late 70’s Honda test session. “Paint a Yamaha red and let me race that.”

Yamaha was clearly ahead of the curve at this time and with Bob Hannah at the helm, made the company all but impossible to beat. Yamaha also clinched the 125 and open class championships in 1978. Hannah aboard the open class OW39, became the first American to win the Trans-AMA championship in a very hard fought battle with five time world champion Roger DeCoster.

In 1979 motocross bikes had finally settled on the magical number of about 12 inches of suspension travel. The original monoshock system that debuted just 6 years earlier when Hakan Andersson won the world championship in 1973 was fully developed. As long as the shock worked well, the monoshocks were tough to beat. The 1979 OW40 was the most refined of all the monoshock bikes. After the huge success Yamaha had in 1978, it would have been reasonable to think that Yamaha would stick with the basic design of the 1978 bikes and just lean on that success for 1979. If it’s not broke why fix it.

For 1979 Yamaha chose to go with a completely new design and built a bike that shared very little with the OW38. The entire bike was brand new with the biggest improvement being increased suspension travel from10.5 and 11 inches to a full 12 inches. To accomplish this Yamaha designed a whole new frame and swingarm to compensate for the increased travel. There was a choice of 2 different length swing arms and most of the team opted for the longer of the two for more straight-line stability. The suspension components looked similar but were in fact all new. The rear shocks had different spring weights and the springs themselves were made from tapered spring wire to get a progressive rate.

Team riders also had the choice of different height foot pegs, different length brake pedals and different length shift levers. Top triple clamps with different handlebar locations were available as were different seats with varying height seat foam. There was also a choice of different rear brake hubs and for 1979, Yamaha offered the optional double-leading shoe front brake system that had been used on the road race bikes for many years. Each rider could custom fit their bike to fit themselves and their riding style.

The engine was an all-new design sand-cast in magnesium and virtually no parts from the new OW40 motor would interchange with the last years OW38. The OW40 had much more aggressive cylinder porting and an all new ignition system to match giving the mid range power a boost. The gearbox retained 5-speeds but had a new design and new ratios. Altogether the entire engine was very compact and light.

The engines were bolted into the frames with carbon fiber motor mounts. This was a first for motocross and carbon fiber was also used on the head stay for the 465 OW41 and also for the lever perches on the handlebars.

The works Yamaha’s were state of the art for 1979 and the most refined and best performing of all the works bikes that year. It was also the end of the line for the triangular swingarm monoshock. For 1980 Yamaha ran the same basic bike only with beefed up suspension. By then Suzuki had released the Full-Floater, Honda had the Pro-Link and Kawasaki released the Uni-Track. These new systems featured a rising rate through linkage arms and offered a better system. As good as the monoshock was it had reached its service life and technology had caught and passed it. As a result, Yamaha was forced to develop its own single shock linkage bike and a new suspension era had begun.

 

 Hannah felt the OW40 was the best bike on the track in 1979.  "The rear suspension on the other bikes was nowhere near as good as my Yamaha's." 


1979 Yamaha OW40 Photos


Bob Hannah's Comments:

To develop the 1979 OW40 I made several trips to Japan. At these test sessions Yamaha would have many different configurations for the riders to choose from. I know the other team members went there but my mechanic Keith McCarty and I went many times by ourselves. I think I tested 3 or 4 different frames with each having a different geometry. We also tested different cylinders, pipes, and carburetors, you name we tested it. We would pick what we thought was the best combination and then the whole team would start the season with that set-up. It didn’t end there though. Throughout the season we were always testing and making the bike better. Japan was always sending new stuff for us to try during the entire season. The development of the bikes never stopped.

The best feature of my 79 bike was the rear suspension. Our rear suspension at this time was much better than the competition. The bike tracked straighter and responded better on the rough tracks than any of the other bikes. Our rear shocks were definitely better than our forks though. I think maybe Honda had the best forks in 79. Keith and I did a lot of our own testing in the Tehachapi Hills that year and we worked very hard at getting the bike to sit as low as we could to increase our corner speeds. Suspension travel had reached 12 inches and the bikes were getting taller. Although they worked better on the rough straights, they didn’t turn very well. After a lot of testing we got the bike to sit much lower in the corners without sacrificing the travel and as a result my corner speeds were up. This was the best improvement we made to the bike that year.

For me it was all about the front brake. I didn’t use much back brake so I went with the smaller rear hub, it was lighter and it was all I needed. But the front had to be perfect. We didn’t just put a new wheel and brake shoes on the bike and rely on that. We took them apart, made sure that every part of the brake shoe made contact with the brake drum at the same time. We filed and sanded the shoes until they were perfect. Anybody can put a new front wheel and brakes on, but on ours, everything hit at the same time, everything worked to the max. My bikes always had killer front brakes.

Our motors ran good but not great. I know the Honda’s were at least as fast probably faster. We made sure that we had a good clutch and that it worked perfectly. Our motors had good mid-range power and a good drive out of the corners. I would sacrifice top end power for a good drive out of the corners any day.

The weight of the bike is very important too. A lot of teams got away from making light bikes but weight is everything. A light bike is so important; you can take 10 pounds off of a bad bike and make it good. You can also sacrifice some suspension performance too with a light bike. Our 1979 bike weighed in at 204.5 to 205 lbs. That was light and the bike responded very well to rider input. Later Yamaha got away from that and never got back on the weight program until I left at the end of 1982.

The OW40 was probably the best bike out there in 1979. The Suzuki's were starting to come around at the end of the '79 season and, by 1980, they were really starting to come on the pipe. The Honda's had good motors and front ends, but the rear suspension was nowhere near as good as my Yamaha's.

Overall, the 1979 season was an awesome season. I was in great shape and riding well. We won both the 250 nationals and 250 supercross. All the testing and development my mechanic, Keith McCarty, and I did in Japan and in the United States definitely paid off. I would have to say the 1979 OW40 was probably the best Yamaha I had ridden during my career. I had a great relationship with Yamaha, they were supportave and they shared the same goals - build the best bike possible and win championships.

 

 Possibly the most famous motocross photo ever taken. Bob "Hurricane" Hannah at the 1979 USGP at Unadilla coming out of "Gravity Cavity" on this very bike.

To celebrate the famous Hannah/Unadilla photograph, world renown sculptor Clyde "Ross" Morgan created this incredible limited edition life-like bronze.


Detail Photos


Keith McCarty's Comments:

During this time suspension travel was reaching 12 inches plus and everyone was going in that direction. The problem was, in making real tall bikes, they wouldn't go through the corners well. We went in the other direction. We wanted to make our bike real low and also have lots of travel. We didn't care if the frame hit the ground or the tires hit the fenders. We wanted to maximize every millimeter that we could to keep the bike low for cornering. We did a lot of private testing in the Tehachapi hills. Even though the suspension was made by Kayaba, we did not have an engineer with us. I was the engineer. We did have a rep though that was very instrumental for me at making the parts that I requested. I had a lot weird requests because I wanted the bike real low. The forks were very special inside. The tall fork caps were to increase the air capacity of the fork, to change the spring curve. I think that is one of the big things that helped us win. Bob had as much travel as they did but his bike was an inch and a half lower. We did have trouble with the valving shims in the shock. Under the tremendous load they would deform and we would loose damping. In some ways, I think the stock shocks were actually better in that regard. Our motors were not as fast as the others that year. The chrome in the cylinders was not so good. They would ruin pistons until the rough edges were worn off. in fact they actually ran better after about three races. Later we would hone them before we used them. We used this same bike for outdoor Nationals and Supercross, it was just set up differently.

 

Bob Hannah's 1979 OW40 has to be one of the best looking bikes ever made.


Details


    • The motor is very compact with tiny sand cast magnesium crankcases and it does not hold much gearbox oil at all. It has carbon fiber motor mounts in the front and an aluminum cradle in the rear. The swingarm actually passes through the rear engine cradle. The motor mount bolts are titanium and the outer case screws are aluminum. The porting arrangement favors mid range power as the transfer ports are huge. (see cylinder in "works parts") The reed cage is very large and is fed from a 38mm mikuni (stamped OW40) made just for this bike. Different pipes for different powerbands were available. The kickstarter is titanium.

 

    • A very small ignition (stamped OW40) uses a map curve just for this bike, and has a very small rotor. The revs build up instantly. This is all connected to a very small black box that is mounted in a fabricated aluminum bracket just ahead of the ignition coil. Notice how close the countershaft sprocket is to the chain buffer. Also notice the access hole in the frame to get at the upper motor mount bolt.

 

    • The rear hub is a very small sand cast magnesium unit that looks like it belongs on a 125. It is laced to a Sun rim with Buchanan stainless heavy gauge spokes. Bob preferred this over the larger hubs used by the rest of the team. The chain adjusters are machined from aluminum with brown anodized inserts that hold the chain adjusters in place when the axle is removed. The ring that you see bolted to the hub is made from stamped steel. It's purpose is to keep a derailed chain from getting tangled. Very Clever. In the lower photo, notice the custom wing nut extended far enough back for easy brake adjustments. The rear torque arm is made of chrome moly and attached at both ends with heim joints for smooth performance. The entire rear wheel assembly is very light.

 

    • Anyone that had a Yamaha YZ in the late 1970's wanted a swingarm like this. The shock mount was much lower than stock. And the long sleek looks really stood out. It is a work of art. Check out the welds in the lower photo. There were several lengths that the riders had a choice from. This was the longest and Bob used this for the whole season. The bike tracked very well in a straight line with this set up.

 

    • The front hub is the same shape as the production one only it is sand cast magnesium. It is laced to a Sun rim with Buchanan stainless spokes. Bob used Pirelli tires exclusively in 1979. This bike is fitted with a new set of 1979 Gara-cross models.

 

    • The front forks are works 38mm Kayabas. The tubes are knurled at the triple clamp contact points. Much time was spent developing these to get the right performance along with the low ride height. The extra long fork caps were made to aid in this by changing the spring curve. The double leading shoe front brake was available in 1979, but Bob chose this single leading shoe model.

 

    • There is a lot of attention to every little detail. The kill switch was mounted out of the way. Even the front brake cable guides have a pop rivet holding the nylon insert into the stainless bracket. Keith's McCarty's bikes were always well set up.

 

    • The rear shock is a DeCarbon design made by Kayaba. It is completely hand machined and is an absolute work of art. Notice how short the shock itself is, and how far down the frame tube the top mount is. This lowered the center of gravity and is also much lighter. The reservoir is attached to the body via a steel braided line with air-craft fittings. The spring itself uses a tapered wire to give a progressive spring weight.  There were several spring weights available. The price of one shock must have been equal to several production motorcycles!

 

    • With the right side panel removed you can see how much air volume is in the airbox. The airbox itself is constructed out of very thin fiberglass. There is an optional translucent cover that goes over the top for mud races, but this was rarely used. When the right side panel is mounted, it seals the dust very well. This design was only good for motocross as the air filter is mounted way to low for sustained water crossings. Some ideas like this could never have been transferred to the production YZ series. The carburetor vent tubes exit into the air box also.

 

    • The rear brake pedal is made from several very thick pieces of aluminum heli-arced together. It is then fastened to the foot peg mount which bolts to the frame. The feel is very stout and positive. Each rider had a choice of different height foot pegs and brake pedals.

 

    • The top triple clamp is cast magnesium while the bottom is billet aluminum. The top clamp was available with different handlebar positions. Bob used the swept back style. There were different off-sets available also.

 

    • The chain guide is carved from billet aluminum and there was a different size used for different rear sprockets. You can see how the chain goes exactly through the middle. The screws on the side hold in the interchangeable nylon chain blocks. The details and custom parts on these bikes is incredible.

 

    • The lever perches are two piece units made from carbon fiber and sand cast magnesium. (yes carbon fiber in 1979!) The pins are titanium, drilled out no less! The cost for just the lever perches must have been staggering! Bob had a contract with Sun-Line levers but the levers were very brittle. Compromises were not an option. Sun-Line took twenty five sets of Magura levers cut and shortened them to look like Sun-Line ones. The levers on the bike are one of the original sets.

  Bob Hannah and the OW40 were reunited during Yamaha's 60th anniversary bash at Yamaha's headquarters where Bob was inducted into Yamaha's wall of Champions. Bob still looks like he is in shape to do some pretty fast laps on that bike. How cool would that be....

Keith, Bob and Scott Boyer check out the bronze that was on display at Yamaha's 60th. You have to see it in person, it is that nice. Only 39 will be produced.


Historical Photos


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