1975 Honda CB550 Four K1
With an experienced team and a lot of data.
Honda’s CB750 raised the bar so high when it was launched in 1969 that it changed the bike industry forever. Finally, a cheap, fast motorcycle with bulletproof reliability was a reality for riders.
The four was so successful that a number of new, smaller versions was a natural next step. The CB500 debuted in 1971, the CB350 in 1972, the CB 400 in 1974, and the CB550 Super Sports in 1975.
All models shared the same engine block but had different bores. The single overhead cam design was replaced across the range in 1979 by a DOHC unit, with only a single cam CB650 continuing until 1985 as the Nighthawk.
The smaller Honda fours are admirable designs with admirable performance. The 350/4 was capable of 97 mph, the Super Sport “F” models feature four-into-one pipes and the CB400F had a six-speed gearbox, though the others did not. All shared mechanical failings, however, that weren’t corrected until the 50-bhp CB550 (Blame Suzuki’s GT 550 for the extra 50 cc. Honda wasn’t going to lose any sales for 50 cc).
The public gradually warmed to the models, and sales reflect that. The CB350 sold 33,000 units, the CB400 34,000, the CB500 80,000 and the CB550 sold 135,000. All the bikes have 1970s styling cues and metal flake colors like Flake Sunrise Orange, Freedom Green Metallic or Candy Jade Green that would be equally at home on a Meyers Max dune buggy or a ski boat.
Though they are small, none of these bikes are ideal for beginners. The power comes on suddenly, and the single front disc brake is best described as wooden. It wasn’t drilled, and rain was a problem. The pad didn’t grab quite right until it warmed up, at which point it could grab and pitch the rider. Therefore, dual drilled discs are an ideal upgrade.
Tires are narrow, frames flex if the bikes are ridden hard, and head shake is easy to provoke. Forks are also tiny by modern standards. The CB350 units are only 31 mm and CB550 forks are 35 mm.
The CB550 introduced welcomed and vital design changes. It has bigger valves, the clutch basket was finally beefed up from the 350 unit, and the shift linkage improved so it would no longer jump out of second gear. The CB550’s clutch was moved to the right side, so a long rod wasn’t required to operate it. Clutch plates are stamped to retain oil, which mean there are divots on the other side that should be ground off. Pre-1976 rockers are just pressed onto the shaft and when the bore in the rocker box wears, the rockers can twist and rub the chrome off the cam follower. At best it is noisy, and at worst it eats the camshaft.
Exciter coils should be up-graded to 1977 units, along with a high output alternator, as earlier bikes do not charge the battery until 3,500 rpm. A solid state ignition is recommended and the original metal plug caps are notorious for shorting when wet.
With so many bikes built, spares are not a problem at all, although there are two notable exceptions. Honda discontinued the cam chain tensioner, and exhausts are known for rusting out.
Fork tubes can also rust, so check under the boot, by the lower triple clamp. Oil leaks around the head are usually due to oil passage o-rings and not the gasket, but pulling the head can be quite difficult.
The intimidating complexity of these bikes means it is vital to buy the best example available. All the 4-cylinder models are relatively affordable, but it’s wise to make sure to get all the badges and both side covers, as they aren’t available.