Getting your bearings…
Well, happily, the sought-after needle bearings arrived from Honda four days earlier than predicted, so one was slicked up and tapped into place. The rollers seemed to be a little on the loose side, so the bearing was packed with thick grease to hold them up and out of the way when the cases were assembled. One roller from the old bearing is MIA and removing the transmission shafts and shift forks again failed to turn up the missing bit, so it must have hit the shop floor somewhere along the line… I hope so anyway!
On the first engine build the shift forks were thought to have been kept in order, but obviously that wasn’t the case. This time, careful inspection revealed that the forks were marked on both sides; C1 and C2 on one side and a different mark along with L, C and R on the opposite side! Left, Center and Right are in relation to how you sit on the bike, so the fork installation following those clues went successfully on engine build number two. Turning the shift drum while spinning the transmission shafts seemed to indicate that all six gears were available this time around. When a small detail is overlooked like this, a lot of extra time and work is expended in making it right again. The bonus for this experience is that one becomes pretty proficient at assembling these engines now, but that re-installation process will, again, be a tussle when going it alone.
While Bill was out of town for the weekend, the bike engine sat in its exploded condition (well disassembled anyway) on the workbench for three days. On a Sunday afternoon, after unpacking, the pile of parts was re-examined and the bottom end cases resealed with liquid gasket. This time the cases snapped together easily without the need to tap, tap, tap and jiggle the shafts and cases around, just the way it is supposed to be. Rechecking the shifting mechanism once more, the remaining components can be bolted back up to the cases within an hour or so. For the most part, the engine parts are designed to go together with a minimum of fuss (other than the shift forks). The gears for the crankshaft, camshaft sprocket and engine balancer all have a master spine, so can only be assembled one way. The fasteners are mostly all flange-head bolts, which can be assembled with a ¼” socket set, using an 8mm deep socket to drive them all home. Gone are the days of those cranky Phillips head screws, loose flat and locking washers and multitudes of 6mm nuts to assemble the whole engine, like were required on the old 250-305 engines.
Timing in the camshafts is relatively easy one the long camchain is threaded up and round the sprockets. The sprockets have a keyway notch, which goes straight up at 12 o’clock position when the piston is at TDC. The cams are marked EX and IN, so you don’t mix those up and there are additional index marks on the sprocket faces that show when they are aligned properly. The camshafts kind of pop in and out of the cam bearings in the head as you set the alignment marks up. Once they are properly aligned, the two parallel top bearing caps are installed to hold things in place, then the camchain tensioner can be added at the back of the cylinder base. The valve cover is held in place with just two long bolts and sealing washers. Screw the long nosed spark plug back down into the spark plug hole and you are getting close to the end of the building process.
It was necessary to use air tools to loosen and tighten the two locking nuts for the crankshaft and clutch shaft. The rotor bolt is pretty hefty, so without a holder tool, a quick zap of the air gun secures it safely in place. Once the outer covers are installed, it is ready to re-install. Because of the way the frame is built and the width of the cylinder head, the installation process is to slide the engine in straight into the opening, then turn it 90 degrees to allow the head to reach up inside the frame tubing. Lifting the engine up a couple of inches, while kicking a small floor jack beneath the drain plug, helps the installation process. An estimated weight of the engine assembly is around 90 lbs, which is a good 25 lbs lighter than the 1960s 305cc twins with a 4-speed gearbox.
Complications arose when refitting all the hoses, wiring connectors and sensors back in place, which had been disconnected/removed for engine removal. The old CB77 engine could be dropped in about twenty minutes, using hand tools and about the same amount of time on re-installation. The myriad of fasteners on the CBR300R fills a small bowl and refitting all the thin plastic panels is a jigsaw puzzle of epic proportions. It takes as much time to get all the fussy bodywork pieces back on as it does to put the engine back in the chassis. The CB300F model dispenses with all the extra bodywork and must certainly be easier to service.
After most of the day’s efforts the bike was ready to fire up again and did so quickly and without drama (so far). There was a little glitch that showed up on the test ride… no speedometer readout, followed by a “check engine” light on the dash. All other sensors and senders seemed to be operating, so suspicions went to the speed sensor, which bolts to the top of the engine cases, just behind the cylinder. Sure enough, the sensor had been dropped into place and the bolt started, but the bolt was never fully tightened down. The bolt was about three turns loose and was easy to access with my socket/wrench tool from Snap-On. With the bike on a rear wheel stand, the engine was restarted and placed in gear. Switching up and down with the gearshift selector yielded rapidly changing speedometer readouts, so that was the solution for that issue. Sometimes, what seems like a simple project can take some nasty and expensive turns for the worse. It looks like this one will eventually be okay once again, but the first 7400 miles were a trial that is best not repeated again.
The next test ride revealed a slipping clutch (?) when it came up on the power, plus it was squealing when you launched in 1st gear… now what? Fortunately, once you drain the cooling system, the clutch cover comes off easily and then access to the clutch assembly. More issues of inattention were revealed in that one of the thrust washers for the outer clutch basket was in the wrong place and the clutch pack stack height was not correct, which caused a plate to jump out of the basket and the tabs got caught on the edge of the big fingers. Closer inspection showed that the friction plates were not all the same! There is a big flat washer and clutch plate conical washers which are installed first, then a special friction plate with a larger hole on the inside to wrap around the first two parts. Using a regular plate caused the whole stack to be too high. Once the correct plate was placed where it belonged, the rest of the plates nestled down into the inner hub and there was a few millimeters of space left at the top. This allows the plates to move apart, but not escape the outer edge of the clutch basket. It all makes sense when you take the time to carefully reassemble the parts correctly. Ah, another senior moment… or two, I guess. The clutch cover was reinstalled with confidence this time, as the causes and effects were fully corrected now. A final check demonstrated full function in all systems and willingness for the engine to pull with some authority above 7,000 rpms. Once the new rear tire is scuffed in, it should be ready for full road work without further worries. Wow, what a workout!
Well, after days and days of effort and a tidy sum spent on parts, will this be a cheap grocery-getter or is it destined to find another home soon? The initial impression was somewhat similar to the CB250RS which returned to me last year. That 1980 bike was kick-start only, had an air-cooled 5-speed motor, but only weighed about 300 lbs. The engine was essentially a slightly hopped-up XL250 Enduro motor with larger carburetor, bumped up compression and a different camshaft grind. That bike was good for 90 mph and once saw 90 mpg on an economy run.
This liquid-cooled, 6-speed, fuel-injected CBR300R has wide, fat tires, disc brakes on both ends, weighs a good 350+ lbs and is supposed to be capable of about 100 mph and 60-70 mpg. The CB250RS was about $1800 back in the early days, whereas the CBR300R runs about $4500 retail. So, is this “progress” or not. Further testing will tell the tale, but there were certainly many lessons learned on this “modern” motorcycle. Overall, the power/weight is pretty close to that of the 1961-67 CB77 Super Hawks, which were archaic 4-speed, air-cooled twins with heavy sand-cast engine parts and a 20 lb crankshaft assembly.
Honda has made 250cc street bikes in many configurations, including singles, twins and four-cylinder editions, so there have been many choices over the years for the “learner” class riders. The CBR250/300R models have proven popular in the US, at least in the beginning. Having been outstripped by its competitors recently, it is time for them to step up once again or continue to lose market share to the other hot-rod small-bore machines available now. For the moment, I will put some miles on the reconstructed CBR300R and get a better feel for what it is like to return to the “small-bore” class of bikes after riding my Benelli Sei and Kawasaki W650s this past year.