Not content to rock the motorcycling world in 1961, with a brand new, high-performance, 100 mph 250-305cc Sports machine in street-bike form, Honda created an entire set of CYB72-coded “accessory” parts to improve the performance and convert the machine into a competitive road-racer.
Well over one-hundred different parts/part numbers were created to make the transition from street bike to track-ready racer. A great deal of the transformative parts were visible as chassis modifications, including: Racing seat; two sets of footpegs, which could be mounted in one of three locations; optional brake and shift pedals; clip-on handlebars (with matching cable sets); alloy wheel rims; two types of reverse-cone megaphones; alloy fenders; fork springs; rear shocks; fork bridge; hydraulic steering damper/hardware; number plate brackets; optional drive/driven sprockets of many tooth options and racing tires. http://motonut.com/CYB77.htm
To make the engine performance improvements the array of parts included were: racing camshaft set; racing valve spring sets; optional primary chain/sprocket set; air funnels for the carburetors; close-ration four-speed and five-speed transmission gearsets; racing carburetors (22mm for 250s), index/timing pieces which replace the rotor/stator and starter motor block-off plate.
Honda’s use of the “YB Accessory” part number designators caused a certain amount of confusion because all of the accessory parts did not constitute “racing parts.” Parts like the optional side stand/hardware parts, folding driver footpegs, winkers (outside the US), various optional headlight designs for different country’s lighting regulations and other parts, large and small, all received a CYB-type of part number. The CYB72 part numbers extended to C2YB, C3YB, C4YB, C5YB, C6YB and C7YB codes, as well.
Honda offered the complete racing kits to dealers in several different packages. There was an optional “Scrambler” setup for off-road riding, created prior to the release of the “real” Scrambler CL72s, which were released in 1962.
If you review the list of the YB parts, you can see part numbers with varying suffixes, like 810, 811, 812, 820, 830, etc. So, what’s with all of those “other part numbers”? A few examples are: The -810 clip-on handlebars came in 38mm size because the 1961-63 forks were machined in those dimensions. With the -811 part series, the clip-ons were reduced in size to 33mm when the fork tubes were reduced in size from 1964-onwards. Despite the change in front fork designs, which went from the Type 1 steel fork sliders to the Type 2 alloy fork slider designs, there was only one YB fork bridge offered in the race kits. Unfortunately, the change in the rake/trail of the Type 2 front fork/steering stem setup took the forks out of alignment with the upper fork bridge, so it just cannot be used.
Two versions of the racing seats exist because the 1961 frames were made in a way which created a 13” space between the front and rear mounts. In 1962 the ends of the frames were extended by 1” so the seats had to be modified to accommodate the change.
The two types of megaphone designs are “round” megaphones and “D-shaped” megaphones, but the part number changed at the center code, instead of the suffix. In this case, 18310(330)-268-810 for the round megs and 18310(330)-269-810 for D megs. The 268 code is for the standard CB72, however the 269 code is labeled as a CY2B72 model, in this case. Now the 269 code is also used for the CBM72 and a C2B72 model variant. The fundamental changes in these models are that the engine configuration is the Type 2 style, with a 360 degree firing crankshaft. Many people don’t realize that the CB72(77) models came in more than just one type, depending upon the country of delivery and the purpose they had in mind to market the bike. Bikes with 360 degree crankshafts have better low-end torque and slower speed power deliveries. Type 2 engines were used in the CBM72, as well as the CYP77 Police models in Asian markets. It is unknown why the 269 megaphones came with the “D-shape” designs, however those are really the ones in demand because of their increased ground clearance in full-lean left and right hand turns. Really aggressive riders will ground out the very ends of the round-type megaphones in racing conditions. The “D” meg shapes cured most of that clearance problem.
Honda’s engine mods, including the camshaft and valve spring kit were helpful, but not overpowering for serious racing, at least in the U.S. The YB camshaft had the same valve lift figures as the stock CB camshaft, however the valve timing was extended to promote more rpms. The author’s personal experience using a YB cam/springs in a stock CB77 motor was that, properly jetted and timed, the engine could rev to nearly 12,000 rpms! However, there wasn’t a significant power increase in top speed, partially due to the fact that the cylinders were larger than the 250ccs that the cam was designed for and that the 1966 bike used for the experiment had the lower compression 8.5:1 standard pistons. When the cam/spring kit was removed there was substantial wear on the center guide roller and tensioner rollers because of my visits beyond the normal 10,000 rpm range. I have to say that the sound that the bike made as it approached 12,000 rpms was quite impressive, even while using stock mufflers!
When “Pops” Yoshimura took standard CB72 street bikes and pitched them into battle against CR72 and other period racers, he won quite a number of the contests because he lightened the pistons internally, ran only the 1st and 3rd piston rings, then reground the camshaft to an even more aggressive profile. He installed larger valves, larger carburetors, different-length header pipes/megaphones and lightened the crankshaft substantially. He also polished all the transmission gears, ported the cylinder heads, added crankcase vents, used an “endless” camchain (to prevent master link breakage), ran a fixed ignition system spark advance and revved the engines up past 12,000 rpms for some events. There were stories about Honda coming over to visit with “Pops” to see what he was doing to his rather stock looking race bikes that caused them to fly past the CR72 factory race bikes, with ease, at times. Yoshimura is a name known world-wide today for performance products, but “Pops” got his start tuning stock Honda Super Hawks, back in the 1960s.
Of special note are the close-ratio transmissions offered from the factory. The racing 4-speed versions were seldom seen as most people opted for the 5-speed instead. The racing 5-speed, coupled with the YB primary chain/sprocket combo made for an impossibly tall 1st gear when people tried to use the combination on the street. The transmissions were considered to be rather fragile, especially when the U.S. hot-rodders started making some serious horsepower using big-bore kits, wilder cams, bigger carbs and many other speed secrets that were common back then. MrHonda has had a couple of racing transmissions in his possession at times and two of the three had broken gears. Honda was forced to narrow the transmission gears quite a bit to get them all to fit inside cases meant for just four sets of cogs.
Demand has been such that through the years, a company in England tooled up for a billet transmission gearset to use in these engines. The NOVA company recently retooled the gearbox again with road ratios so those who are well-heeled can spring for their very own 5-speed street transmission for their CB72-77s. SEE: http://www.novaracing.co.uk/honda-cb7277-5-speed-road.htm or http://www.honda305gearset.co.uk/home for details.
So, that’s the story of the Honda CYB72 race kit parts. The accompanying photos include the parts lists, which covers the majority of the kit parts, but not each and every one that Honda listed. If you put a CYP72 in place of the CYB72 code you get all the parts to build a Honda factory Police bike! Honda had all their bases covered, didn’t they? Bill “MrHonda” Silver