GP’s Classic Steel #55: 1979 Mugen ME360R

For this week’s GP’s Classic Steel we are going to take a look back at one of the coolest bikes of the seventies, the 1979 Mugen ME360R.

For this week’s GP’s Classic Steel we are going to take a look back at one of the coolest bikes of the seventies, the 1979 Mugen ME360R.

In the world of vintage motocross racing, few bikes are as sought after as the Mugen ME360R. This ultra-exotic and rare semi-works bike offered “Factory” bike performance for the few who could afford its exorbitant price (the equivalent of $20,000 in today’s money).

Few names from the heyday of motocross carry as much cachet as that of Mugen.   The mere mention of the name conjures up images of ultra-expensive and exotic bikes from the Far East. They were as rare as they were beautiful, and every young motocross fan in America dreamed of having one in their garage.  In the world of seventies motocross, Mugen was the ultimate fashion statement.

The heart of the MR360R was this 353cc two-stroke single. Originally based on the CR250R, the Mugen motor package bumped up the displacement by 106cc’s and increased power by 20%. At a peak of 34 HP, the 360 was not about to blow the doors off any full 500’s, but its quick revving and snappy delivery made it competitive on the track.

Hirotoshi Honda started Mugen Company Limited of Japan in 1973.  Mugen, which translates to “unlimited” or “infinite” in English (hence the term” Mugen Power”, which is often associated with the brand, meaning “unlimited power”) was started as a purveyor of hot rod accessories for Honda Civic automobiles.   Hirotoshi, as the son of Honda Motor Company founder Soichiro Honda, enjoyed very close ties to Honda Motors and used this intimate knowledge to build some of the trickest Honda’s of the seventies. Their Honda Civic based 1300cc Formula racing car engine dominated Japanese open wheeled racing in the early seventies and opened the door for their expansion into motorcycle racing.

If you could not afford the astronomical $5600 (three times the cost of a stock CR250R) asking price for a full on ME360R, you could always take your stock CR250R Elsinore and convert it to a 360. The Mugen 360 kit cost $500 and included a cylinder, head, piston, pipe, manifold, gaskets and strengthened transmission gears.

In 1976, Mugen made its first foray into motocross in the All Japan Motocross Nationals. At the Japanese round of the GP’s that year, a Mugen ME250 took first place and put the brand on the map of international motocross.   The following year, Mugen released its own limited production bikes based on Honda’s CR125 and CR250 Elsinore. The machines featured highly modified Honda motors and frames, to go with specially designed suspension components. They were more or less turnkey works bikes for the few who could afford and obtain the extremely limited production machines (Only around 100 were built annually).  

Because of its CR250R origin, the ME360 ran very different than your typical Open class beast. This was no leave-it-in-third-and-torque-around kind of machine. To maintain competitive speed, the Mugen had to be ridden aggressively. Low end power was unimpressive, before lighting the afterburners in the mid-range. Below 6000 RPM, it was as down as much as eight horsepower to its Open class competition. Above 7000 RPM, however, it opened up a slight lead.

In 1978, Mugen would expand their business to include a 360cc version of the ME250. At the time, Honda did not offer an Open Class machine and many riders wanted the option of riding a Honda big bore. The new 360 filled that void and could be purchased as a kit or a complete motorcycle. The kit retailed for $500 and included a new cylinder, head, pipe, piston, rings, gaskets, heavy duty clutch springs and beefier transmission gears. If you were willing to pony up a full $5600 (neatly three times the cost of a stock CR250R Elsinore), however, you could buy a full-on Marty Smith replica.

The Mugen name comes from the Japanese word for “infinite” or “unlimited”. When you bought a Mugen, it meant that you were getting “unlimited power”.

In 1979, Mugen Company Limited of Japan would contract with Al Baker (of XR’s only fame) to start importing Mugen’s into the USA. Prior to that point, they had been limited to doing business in Europe and Asia, due to contract restrictions with American Honda.  For $5600, Baker would sell you a complete ME360R “Marty Smith Replica”. The bike may have looked very similar a stock CR250R Elsinore, but the two shared very few parts in common. Of all the pieces that went into a ME360R, only the hubs, airbox, fenders and outer engine cases were off the shelf Honda items.  The ME360R was basically the same machine that Factory Honda rider Marty Smith had campaigned in 1979, and any rider with and deep enough pockets and the right connections could own one. The ME came with the 360 kit already installed, and mated it to a custom built chassis. The suspension duties were handled by special “works replica” Showa components front and rear. In 1979, this truly was the closest thing to a Factory bike the average person could hope to buy.

The heart of the Mugen ME360R was, of course, its 353cc motor. It offered 106cc’s more displacement that the stock CR250R and gave the ME a fighting chance against the fire breathing  Open class bikes it would be going up against. The larger cylinder featured a bigger bore, as well as different porting and larger cooling fins to accommodate the additional heat generated by the punched out motor. Since the 360 retained the stock CR’s stroke, it ran very different than the purpose built big bored of its day. Whereas bikes like the Yamaha YZ400 pumped out a burly and torquey spread of power, the Mugen liked to be revved hard and ridden aggressively. Much like the stock CR250R, the low end was marginal on the 360. It was snappy and pulled cleanly, but made little power below the mid-range. Once it came on the pipe, however, it pulled hard and long into a shrieking top end blast. The light flywheel and short stroke gave the 360 a very quick revving personality that was both fun and fast.  Below 7000 RPM, it gave up as much as eight horsepower to the traditional big bores, but above the midrange, it pulled hard while the traditional Open bikes were running out of steam. If a rider was aggressive and knew how to keep the 353cc mill on the pipe, the ME could run with the 400’s. If, however, you tried to ride the Mugen like a traditional Open bike and torque it around the track, you would be left eating roost.

Most of the blame for the Mugen’s stratospheric price went to its works suspension. The 39mm Showa (considered massive in ’79) units mounted on the ME360R were exact copies of the units offered to Factory Honda riders like Marty Tripes and Marty Smith. These units were not offered for sale to the public and only found their way to the ME360R due to the close ties Mugen founder Hirotoshi Honda had to Showa (Hiro’s uncle ran Showa at the time) They offered a level of performance unattainable with off-the-shelf components.

One advantage the ME360R had over the Open bikes of its day was handling.  Mugen went to great pains to fine-tune the Elsinore’s chassis dynamics and it showed. While the ME used a standard CR250 frame as a jumping off point, by the time Mugen’s engineers were done, the two were very different beasts. Mugen’s frame was a custom built just for the ME360R and featured many changes to enhance performance.  Compared to the standard CR, the Mugen offered a tighter handling package. It used a beefed up frame with a steeper steering angle, as well as repositioned shocks. The shock mounts were moved one inch forward on the ME360R and bolted on a works style alloy “banana” swingarm. The special swingarm and forward mounted shocks allowed the engineers to provide additional rear wheel travel, without raising the seat height or harming the chassis’ balance.

Honda’s odd decision to not produce an Open bike through the seventies led to a good deal of pent up demand that Mugen was more than willing to serve. Since Mugen produced less than 100 actual ME360R’s per year (with the greatest number going to Europe), the vast majority of 360’s in circulation are converted kit bikes.

On the track, the Mugen ME360R could carve rings around most of its Open class rivals in ‘79. At 223 pounds, it weighed fifteen pounds less than a RM400 and felt every bit of it. The careful chassis tuning and snappy motor gave the bike a very light feel on the track that was very unlike the typical big bore. The ME offered excellent steering precision while tracking straight and true at speed. While it may have been down a few horses to its rivals, its superior handling helped offset much of this disadvantage.

The other half of the high dollar Mugen suspension equation was a set of unobtanium works Showa shocks. These specially built units (labeled “Showa/Mugen Specials”)   were the same ones offered to the Factory Honda team and not for sale to the general public. These works shocks were mated to a custom built Mugen frame and a specially built alloy “banana” swingarm (This Mugen has had the original Showa shocks swapped for a set of Fox air shock. This was a common occurrence even on the works Honda’s of the time)

Certainly helping the handing of the awesome ME360R was its works suspension. The components used on the Mugen were said to be exact replicas of the units on Smith’s works Honda and accounted for a great deal of Mugen’s exorbitant cost. The forks were specially built 39mm (stock CR’s made due with 37mm units) Showa units that punched out nearly twelve inches of travel. The forks offered remarkably fluid and stiction-free performance. Small bumps were absorbed so well that testers said the forks would have worked great off-road, while still absorbing motocross style hits with nary a whimper. Compared to the stock units found on the stock CR, they were both plusher and stiffer, while offering far greater steering feel.  Without the stock CR’s inherent fork flex, braking was also much more precise and predictable. In 1979, these forks were a quantum step above anything available on a production machine.

In the rear, the Mugen once again offered works bike performance. ME360R’s were equipped with specially built aluminum aluminum-bodied, nitrogen pressurized Showa units. Officially labeled “Showa/Mugen Specials”, these shocks were identical in construction to the ones offered to the Factory Honda race team.  Just like the forks, the shocks offered remarkable performance. They were set up for a fast 180 pound rider and allowed an aggressive pilot to make the best use of the Mugen’s remarkable performance. Small chop and big hits were no problem with these works units. They were literally ready to race a Grand Prix right out of the crate and about a thousand times better than the miserable Showa shocks that came mounted on the mundane stock CR.

Although the ME360R looked very similar to a stock CR250R Elsinore, the two actually shared very little in common. Virtually every part on the bike was tweaked, massaged or replaced to maximize performance. It truly was a works bike for the common man (with a price to match).

To this day, a Mugen remains one of the most prized machines in motocross. They were rare, exotic, and absurdly expensive. For all that money, a customer got true “works bike” performance. It was light, fast and superbly suspended.  On the track, its high revving power spread offered a very different experience than the typical big bore race. It was a go-for-broke style of machine that rewarded aggression and penalized laziness. If you were talented enough to use all of its potential, Mugen had the bike to make you a star.