Remember Robert Perkins and his hopped-up 1990 Honda NS144F? Well, due to popular demand, he’s back with the creation story of his Frankenbike.
Picture a rosebush ablaze with pink and teal blooms. If you dared to do so, you just captured half the absurdity of how this double-engine fifty sprung to life. Back when I first beheld this diminutive motorcycle in 2013, it appeared to have been dragged through a rose sticker garden headlight first. I should have seen the thorns then…
Of course, it all started out innocently enough with a 2,000-mile round trip from Alabama to West Virginia. Having recently sold one of eight motorcycles, I swore to the immortal gods that never again would I own more bikes than our week has days. Just maybe, peer pressure from the non-motorcycling public had taken its toll. When co-workers would question the sanity of polygamous motorcycle ownership, I learned to simply drop my eyes, unwilling to explain. Yes, I have been one acquainted with the bike.
Peer pressure or not, I was doing well maintaining my pledge until the stars aligned against me. Riding out that unusually cool August morning from my home in Alabama, I could not see the invisible game pieces of fate being ushered into motion. Regardless of the omens, my trip up to Blowing Rock, North Carolina was the paradigm of a beautiful late summer tour. By some temporary reversal in global warming, the weather had shifted from a heat wave to an unusual cool spell. Not all was perfect, though. The gods were watching, and as a mortal capable of mistakes, I perceived early in the trip that my routing was a bit off. Too romantic to employ a GPS, I had been relying on my trusty maps of the papyrus variety and my inability to add and subtract. And yet somehow those extra fifty miles kept creeping in at the end of each day’s ride . . .
It was not until the return trip home, though, that I fell inextricably into the hands of fate. Due to my precision navigation techniques outlined above, I ended up riding from the New River Gorge Bridge in West Virginia to Asheville, North Carolina, after a full day of tedious backroads. I pulled into a hotel around midnight only to discover that the one bed remaining was in a smoking room. How bad could it be, I mused? In truth, I would have been better off sleeping under the table of a high stakes poker game sponsored by a cigar company.
By the time I made Dahlonega, Georgia, the following day, I was already feeling the effects of multiple 500-mile days and a bad night’s sleep. In this weakened state, I was fortune’s fool. And so I began to hear mythical Sirens luring me to a motorcycle dealership that appeared like a mirage on Georgia’s snaking Highway 60. I should have strapped my hands to the handlebars of my Honda 919 and kept on motoring. Instead, I hung an immediate right, dismounted, and moseyed on in to check out the rarer brands for sale: MV Agusta, Moto Guzzi, Aprilia, and Motus.
After avoiding the unobtainable hardware and sitting on a Moto Guzzi V7, frugality directed me even further to some older Hondas taken as trade-ins. As I wheeled around to face what would ultimately be my fate, I beheld a bone stock Honda NS50F, complete with its OEM decals of teal and hot pink applied to a rather pedestrian white. Just in case you are not old enough to know, those colors were pretty dope back when I walked the halls of Jurassic High. And if those decals were not sick enough in 2013, let us not forget this particular motorbike had been blinged out with rose stickers. Of course, most sane individuals would have taken a quaint interest in this little fifty and politely walked on.
Two minutes later, I found myself riding the flowered fifty around the parking lot. I do concede the gods had their way with yet another puny mortal. Shortly after returning home from my tour, I found myself taking another nine-hour round trip to pick up the bike. I still remember the salesman handing me the key and inauspiciously asking if I had ever heard of the True Grits 50cc Fun Run . . .
Having broken my sacred oath by once again possessing more than seven motorcycles, I knew I better fly straight. I reasoned it was now very pertinent to stay true to my first commandment of motorcycle ownership: “Thou shalt not own any bike thou canst not commute on.” Sounds easy, right? Well, a 50cc really pushes one’s faith when commuting in a mountainous town of the Appalachian variety. Luckily, the mighty NS is equipped with a six-speed gearbox and a razor thin power band, so you are basically given a 5-mph window in each gear to maintain forward momentum. On the bright side, it does turn my 10-mile commute into a heart-pounding track day just keeping up with the flow of traffic. I do confess though to slightly altering my route home to tame a monster incline up a local mountain. In Florida the NS50F would probably be perfect.
Following my first trip to the fabled True Grits Fun Run and considering my commandment to commute on all my bikes, I rationalized a modified 50cc was primarily a safety consideration. My first alteration was to remove those flower stickers. Yes, I probably lost some street cred with this move, but I figured, flowers or not, with a top speed of 58 mph, high stakes street racing was not in the NS’s future.
Thus, I was on my way to becoming a disciple of the small bore. Having modified several motorcycles in the past, I always wanted to lean full in by modifying a bike past any reasonable usefulness. I figured the NS was as good a bike as any with its cheap buy-in, limited utility, and relatively inexpensive performance parts. Famous last words . . .
As described in my earlier article, I ordered performance parts from Japan and a cafe seat from a local supplier. The front fender was replaced with a Honda MB5 fender and subsequently bobbed. A local painter provided some much needed updating to the 1990s color scheme. To gain more top-end speed, I changed the final-drive gearing and swapped the ignition module for a performance item that eliminated the rev limiter. With a 72cc kit and its matching head, flatslide carburetor, and performance exhaust, I could pull nearly 14,000 rpm downhill and see a true 72 mph. Of course, I had to add a tachometer and change out the stock speedometer, which signed off at 70 mph, to see these humbling numbers.
In this form I took the NS72F to the first Smoky Mountain Crawl and rode out to Deals Gap. I believe the 125 miles I rode that day remain the longest I have ever spent in any motorcycle saddle. Trust me; you will not mistake an NS for a tourer.
After running with some “big-displacement” motorcycles like the Honda Groms I encountered at the Crawl and my third True Grits that year, I knew the writing was on the wall. Despite managing my commute better, the NS72F needed more power. It was time to near triple the stock displacement by adding a second 72cc engine!
Before this sordid tale continues, please understand I have always enjoyed tinkering in the garage as much as riding, so the pursuit of such mechanical absurdity was more a mental puzzle than a quest for any real or practical gains. (I felt that disclaimer necessary before you read further and considered calling the appropriate psychiatric services on me.)
To attach the second NS motor, I first had to solve the problem of a vertically split crankcase. Allen Millyard, a man I greatly admire, was able to create his four-and five-cylinder Kawasaki two-strokes because they employ a horizontally split crankcase that allowed him to build up the crankshafts and combine the necessary crankcase pieces. If the NS was a four-stroke engine, I could have created a V- twin engine by mating the two connecting rods. Unfortunately, a liquid-cooled, vertically split two-stroke made the task of combining engines a bit more complicated because it was necessary to retain each engine’s crankcase as a sealed unit for the requisite induction process. Therefore, I chose to link the two engines via an external crankshaft coupler.
Of course, the real work involved in this process would be learning to use a lathe and mill, something I had zero experience in. Fortunately, Joe, a good friend from our local classic motorcycle scene, stepped up as a mentor and taught me basic machining on his century old Hendey lathe and slightly newer Bridgeport mill. I am forever indebted for his kindness and patience in this arduous process. Most of the genius behind the design is Joe’s, with me acting as Dr. Watson to his Sherlock Holmes.
To combine these two separate engines, I machined a ring to attach to the flywheel side of the first engine’s crankcase using the bolt pattern that held its crankcase together. Then, I bolted a second ring to the first ring as a spacer, machined down the second engine’s crankcase so the spacer could sit flat against the primary drive side of the second engine, and used the bolt pattern for this second engine’s crankcase to secure it to the spacer ring. This ring spacer, along with some external engine mounting points, accomplished the task of linking the two engine crankcases.
To make the crankshaft coupler, I first shortened the mating side of each engine’s crankshaft to keep the motors as close as possible to one another. I also machined a keyway in each crankshaft to accurately time them, and I threaded the center of each crankshaft to allow a bolt to keep each half of the coupler secured. Both halves of the coupler were also machined with a keyway. Each coupler half was then pressed onto its respective crankshaft while carefully aligning the keyways, and secured with a bolt. This process is similar to the primary gear’s installation on the drive side of the engine. One coupler half also employs a dowel pin for correct timing, and the coupler halves are bolted together using nuts that can be accessed through a small hole machined in the underside of one engine case.
Following the assembly of the coupled engines, the flywheel simply needs to be attached to the outer engine. A 360 degree big-bang firing order was used to simplify the ignition and also because it provides torque characteristics similar to a single cylinder engine. Thus, both pistons fire at exactly the same time. A larger radiator was used to upgrade the cooling system.
One problem I quickly found when running the second engine was that vibration had increased considerably without a second counter balancer. This problem was solved by machining a hole in the first engine to accommodate an oil seal and a small shaft that connects its counter balancer to the second engine’s counter balancer. I will confess it is very difficult to time the crankshaft coupler and counter balancers when assembling both motors.
All done, I would say the NS144F probably has a curb weight of around 200 pounds, and I contribute another 200 pounds when wearing ATGATT. For those who wonder just how low a dyno can measure rear wheel power, please note the NS144F pumped out 17.89 horsepower and 10.20 lb-ft of torque. Unfortunately, this relatively paltry power outmatches the stock bike’s drum brakes. Moreover, the corner speeds it can now obtain fully overwhelm the motorcycle’s bicycle-like chassis. I would say the saga continues, but sanity recognizes quite a bit of time has been lavished upon such a limited motorcycle. Plus, other creations lurk in the corner of the garage… and my mind’s eye.
We’re suckers for nice photos and descriptive words and reasonably decent pics of your favorite motorcycle, or maybe just your most memorable one for all the wrong reasons? Send yours to firstname.lastname@example.org, title it “Readers’ Rides,” and see yourself in this spot one of these weeks.
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Source: All Bikes news one