Honda’s Throwback: 1978 Honda CX500

In the late 1970s, Honda decided to return to its roots and produce a reliable motorcycle aimed at the get-to-work crowd. Enter the 1978 Honda CX500.

1978 Honda CX500

In 1979, Honda offered the CX in three versions. There was the standard CX500 (pretty much the same as the 1978 version), the Custom (peanut tank, hi-rise bars) and the Deluxe.

Photo by Nick Cedar

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1978 Honda CX500
Claimed power: 48hp @ 9,000rpm
Top speed: 111.9mph (period test)
Engine: 496cc liquid-cooled OHV 80-degree V-twin, 78mm x 52mm bore and stroke, 10:1 compression ratio
Weight (wet): 481lb (219kg)
Fuel capacity/MPG: 5gal (19ltr)/40-50mpg
Price then/now: $1,898 (1978)/$1,500-$5,000

Once upon a time, a motorcycle was transportation. Faster than a streetcar and more reliable (and cheaper) than a horse, motorcycles were bought by thousands of people who used them to get to school or work. Delivery services and police departments relied on motorcycles to get where they wanted to go quickly and economically.

Most motorcycle manufacturers got started building reliable, economical get-to-work bikes. Honda was no exception. Yet as the 1950s gave way to the 1960s, in developed countries like the U.S., England and Europe, motorcycles stopped being transportation, morphing into a Lifestyle Statement instead. Bikes sprouted exotic bodywork, multiple cylinders, overhead cams, high handlebars and fancy seats. Advertisements stopped mentioning miles per gallon and started crowing about quarter-mile times.

Yet in the late 1970s, Honda, then (and still) the largest motorcycle manufacturer in the world, decided to return to its roots and produce a reliable motorcycle aimed at the get-to-work crowd. Honda’s brief called for reliability and low maintenance, and up-to-date technology. The CX project was headed up by Shoichiro Irimajiri, who designed Honda’s 6-cylinder road racer in the mid-Sixties. After two prototypes were designed and built, one displacing 350cc and another 500cc, the decision was made to make the new model a 500. The CX was given liquid cooling, a 5-speed gearbox, constant velocity carburetors and shaft drive. Surprisingly, it was not given an overhead cam engine.

Design considerations

The decision to use an overhead valve design with pushrods on an otherwise very modern machine may seem a little strange, but was compelled by the longitudinally-mounted, 80-degree V-twin design, which had the crankshaft in line with the frame as on a Moto Guzzi. To accommodate this, the 4-valve heads were skewed 22 degrees to keep the carburetors from banging the rider’s knees. That skew would have made it very difficult to use overhead cams, so it was back to pushrods. The pushrods were short and hollow, and an exceptionally (for then) over-square bore and stroke of 78mm x 52mm let the engine rev to 10,000rpm. Mated with a free-flowing intake tract and large carburetors, the engine had good volumetric efficiency.

The crankcase and transmission housing were a single casting, with the cylinders cast in with the crankcase. Crankshaft, camshaft and gearbox removal was accomplished by removing individual end plates. The arrangement is reminiscent of very early motorcycle construction, and creates some repair complications. For instance, you have to remove the gearbox internals before removing the left connecting rod bolts, and you have to pull the engine out of the frame before removing the gearbox.

Spinning the reverse direction of the crankshaft, the transmission and clutch served as a counter-rotating mass, offsetting the V-twin’s torque reaction. The engine was a stressed member of the frame and was located as the exact center of mass of the motorcycle, making the relatively heavy 449-pound bike handle surprisingly well.

The rear shocks featured two-stage damping, unusual at the time, and the CX’s tubeless tires were a first for a production motorcycle. These were made possible by Honda’s new ComStar solid spoke wheels, with a disc brake up front and a quite decent drum brake in back.

Out in the market

When Honda wheeled its new creation out into the light in early 1978 its ads trumpeted the CX as “First Into The Future.” Contemporary magazines were, in general, impressed with the new offering. They liked the engine’s 10:1 compression ratio and its ability to rev to 10,000rpm —  while sipping regular gasoline: One magazine recorded an average of 51.5mpg. The CX got low marks for its weight (it was the heaviest 500 on the market) and its odd looking engine, and its weirdly designed headlight nacelle was hated by all. Out on the road, testers enjoyed the powerful but quiet engine — but not the transmission, which if handled clumsily either clunked or missed shifts. They also disliked the tethered gas cap and the soft springs in the Showa forks, which bottomed out on hard braking.

The market reacted favorably. Buyers read the reviews, decided they liked the idea of a technologically advanced bike that was fun to ride, quiet, and reliable, and bought a lot of CXs, proving that Honda was right — there was still a market for a get-to-work bike.

Buyer enthusiasm was damped but not destroyed by a recall at the end of 1978. The CX’s camshaft was driven by a chain off the crankshaft. The chain was tensioned by a rubber blade, but because the bolt securing the blade tightened against rubber, when the rubber lost its spring the bolt on early 1978 CXs could come loose, with unfortunate results. Honda CX500 owner Larry Cargill points out that the recall is still in effect. “Most bikes that have survived all this time have the issue taken care of, but if the one you have hasn’t, Honda still honors the recall. If you buy a 1978, look to see if it has three triangular dots near the serial number, which means that it has been fixed. Honda took care of the issue in late 1978.”

In 1979, Honda offered the CX in three versions. There was the standard CX500 (pretty much the same as the 1978 version), the Custom (peanut tank, hi-rise bars) and the Deluxe. Marketed as a middleweight tourer, the Deluxe had a seat that was 1.5 inches lower and more comfortable on long rides, a side stand that was easier to deploy from the saddle, and more attractive solid-spoke ComStar riveted wheels. The tethered gas cap was also improved. As Patti Carpenter of Road Rider said, “These changes have made what was already a nice, hard working ‘middleweight’ into a more attractive, more comfortable and more manageable touring machine.”

CXs proved to be incredibly popular with dispatch riders. In England, the CX became known as the “despatch” rider’s mount of choice. While not the prettiest or the best handling bike, the CX would run all day in any weather and put up with minimal maintenance and repeated abuse. It was perfect for urban use.

The standard version was dropped after 1979, but the Deluxe was offered until 1981 and the Custom was produced until 1982. The GL500 Silver Wing Interstate, a full-on touring bike complete with full fairing, appeared in 1981. The CX was bumped up to 650cc in 1983, but by then it was living on borrowed time. The American motorcycle market had gone into a nose dive, and any Honda model that wasn’t a best seller faced the ax. CX production stopped after 1983.

Larry Cargill’s CX500

Larry Cargill is a very busy man. Retired from a government job three years ago, Larry has never had more to do. Word has gotten around that he builds spot-on replica fiberglass for Honda GL Silver Wings, not to mention excellent engines for 1970s and early 1980s Hondas. “Ever since I retired, it’s been nonstop work on bikes,” Larry says.

A mechanically apt person like Larry could probably keep any bike running, yet with many to choose from, his bike of choice is the Honda CX500. “These bikes were way beyond their time when they were built,” Larry says. “They are maintenance free except for oil changes and valve/cam chain adjustments. They have plenty of power and the handling is good after some simple modifications are made,” he explains.

A lot of people kept their CXs, often putting huge miles on them. But at some point, even a well-maintained CX needs a rebuild. Enter Larry. “I used to ride enduros on a Yamaha when I was young, and I have always liked to fix things. A guy at my old job wanted to get his bikes running. He had a first year CX500 and some other bikes. I restored his Honda CM500T for him and kept the CX. That’s how I got into restoration,” Larry says.

Larry rebuilt the engine and the frame of the CX, learning a lot in the process. “It was back when Honda still had parts.” The CX was running, but not running comfortably. Looking closer, Larry discovered there is a very tiny orifice in the CX500 Keihin carburetor low jet that eventually gets plugged. Getting the pressed-in jet out of the carburetor wasn’t easy, but Larry figured out how to do it. With the jets cleaned and reinstalled, the bike’s responsiveness and power was amazing.

Larry posted his findings on the CX500 forum. He discovered this was a common issue and was told he should write a book — so he did. The book, Larry’s Guide to Rebuilding the Keihin CX/GL Carburetors has gained wildly positive reviews, with several forum members suggesting Larry deserves a Pulitzer Prize!

After collecting new OEM parts from all over the world, Larry set out to complete a full frame-up restoration. Every part was redone — “All the way down to the nuts and bolts,” Larry says — with new chrome, zinc plating or paint as used by Honda. Larry worked hard at it, as he had a deadline in mind — the annual Classic Japanese Motorcycle Club show held in Auburn, California. Larry decided there wasn’t enough time to repair the existing engine in his CX, so he went looking for another one. “I found a motor on eBay that appeared to be a replacement motor from Honda, with no serial numbers. After rebuilding this motor completely with all OEM parts, I figured that getting it registered would be a bear, but the lady at the DMV found the bike in the system and reregistered it without the serial number on the motor. I’ve never found another Honda motor without a serial number. In my opinion, it adds to the nostalgic history.” Larry worked feverishly to finish the CX. Nine days before the show, Larry was painting the tank when he realized that he had painted it with the wrong year’s design. After ordering more tank decals from BDesigns, Larry finished the bike. “I finished painting the correct tank at 5 a.m. the day before the show. I waxed and polished the bike at the show — but I made it,” Larry says.

Riding and wrenching

This CX runs and rides well, but Larry wants to keep it as a show bike for the most part. Fortunately, he has another CX, one that he rides frequently, and both bikes feature suspension upgrades Larry has worked out. “The front end on the stock bikes is really soft. One of the problems is the light oil Honda recommended. I use 20-weight Bel-Ray. I collapse the fork and fill it [with fork oil] 5 inches from the top, then extend the fork and use a spacer between the springs. I get 3/4-inch sprinkler pipe nipples and cut them between 3/4- to 1-inch long, depending on the firmness I want. It stiffens the front end and keeps it from bottoming out under hard riding conditions. It’s like riding a totally different bike. With the hesitation in the carburetion fixed and a stable front end, this is a solid bike and much more fun to ride,” Larry says.

The stock front disc brake uses a single-piston caliper, but despite positive period reviews, Larry thinks it’s less than adequate. “I didn’t change the brakes on this bike since it was intended as a factory restoration, but if you use Teflon braided brake lines, it’s 60 percent better. Rubber lines expand. JDA Enterprises makes rubber-covered lines that look almost original. You can also upgrade to dual-piston calipers from the 1983 GL650 Interstate.”

Larry suggests changing the oil every 2,500 miles and using Shell Rotella T 15/40 oil after the engine is broken in. “It’s made for diesel engines and has a zinc additive, but if you use it in a brand new engine the rings won’t seat.” Another tip is adding a little GM Engine Oil Supplement, a high zinc additive now marketed as engine assembly lubricant.

The 1978-1981 CXs were fired with a CDI ignition. “There are two trigger windings and the high end coil goes bad. In 1982 Honda went to a transistorized ignition, which is bombproof.” Larry replaced the stator on his 1978 with one rebuilt by Custom Rewind. “They are much better quality than the OEM originals,” Larry says.

“These bikes are running more than 30 years after they were made. They have plenty of power and regularly blow away Harley Sportsters. Not bad for a 36-year-old bike. After the suspension modifications, they handle well, and if you keep the oil changed and keep the coolant level correct, the bike will run cool and not have problems. Simple maintenance is the key to longevity. There are bikes out there that have gone well over 100,000 miles and more,” Larry says.

“There were many made and a high number are still running. We have 23,652 people on the CX forum who love and support these bikes. I think that’s why so many of these bikes are being brought back to life after years of sitting in storage. People all over still get to work on them and ride them for pleasure.

“I want to put the bike on the map and give it the respect it deserves. The CX has earned a well-deserved place on the map of history, right alongside so many other collectable machines.” MC

welshman
4/9/2015 4:08:42 PM

I was working at a Honda/Yamaha dealer when the CX500 'Plastic Pig' was launched. There were at least 3 cam chain tensioner updates. Even the final fully automatic tensioner only worked for about 18,000 miles if bike wasn't ridden properly. It was (is) an engine that not only likes a lot of RPM, it needs high rpm to survive. Crankcases without numbers are from the early model, the tensioner pivot bolt boss would snap off the case when people tried to ride them like a V-Twin double the capacity (slogging around in too high a gear at too low an rpm) If Harley wasn't such a we don't care what they do company, they would have known the load reversals destroy chains and tensioners. Twin cam should have been designed with gears from the ge tgo, I doubt one could rev high enough to prevent the load reversal that destroy the tensioner