ALLEN MILLYARD
Our Allen talks bike shows and recalls when he fired up the SS100 V-twin for the first time at the CMM show some 20 years back!
Allen talks tiny twins once more!
Attending Motorcycle Live at the NEC at the end of last year really reinforced my passion for classic bikes like those featured in Classic Motorcycle Mechanics.
I feel these bikes are from a time when we learned a set of core skills, often as a child on a Honda 50, with bald tyres in a muddy field, then on the road on a 50cc moped, progressing to a superbike over many years and miles. The electronic gadgets and rider aids on modern bikes may be a good thing for some, but for me, I pride myself on being able to ride any motorcycle in its raw state where I’m directly connected to the bike, not through a computer that has the final say on how hard it thinks I can brake or accelerate. When I returned to the motorcycle parking area my Honda ST1100 had disappeared in a sea of adventure bikes and I was really taken aback by how small and inconspicuous it looked! I’ve owned my ST1100 for the past 20 years and I guess I will own it a bit longer. (See page 82 for more on my Pan!)
Back to my Honda SS100 V-twin – I had just picked up the frame and tank from my friend Neil Haworth. I’ve known Neil for years and he has painted just about every bike I’ve
made since 1997; he never needs to advertise his work and doesn’t have a website, but he is always flat out rebuilding and painting customers’ vintage cars and bikes every time I call round. Once back home I placed the freshly painted parts on my dining room table and sat admiring them, excited to start the reassembly, but I was still waiting for some parts to be chrome plated.
I returned to the garage to start on the engine assembly. The engine parts had been vapour blasted by Rob at RD Cox & Son in Reading and looked perfect, just as though they had been freshly cast. The first thing to do was to grind in the four valves, then the cylinder heads were cleaned with brake cleaner and an air-line to ensure all remnants of grinding paste were removed. New valve stem seals were then pushed on to the valve guides, followed by the valves, springs and retainers. I used my Dad’s old cast steel valve spring compressor that I have modified to work with many engines over the years to compress the springs and fit the collets. I then fitted the camshafts and set the valve clearances. With the two heads built I assembled the bottom-end. The gearbox shafts, selector drum, kick-start shaft and crankshaft were placed into the left-hand crankcase, then I made a special crankcase gasket to fit the modified central joint of the crankcases. To do this I placed a piece of 0.5mm gasket paper over the right-hand crankcase joint then, holding it secure, I rubbed my finger around the edges, pressing down hard over holes, making an impression on the gasket paper for it to be cut out. Then using a suitable punch I punched out the screw holes and slightly larger dowel holes before cutting out the gasket with sharp scissors.
I then applied a thin smear of Permatex ultra grey gasket cement on both crankcase mating surfaces to ensure the joint was leak free, then placed the gasket on the left-hand crankcase joint and carefully lowered down the right-hand crankcase, ensuring all shafts engage correctly, then tightened the screws. At this point I always check to ensure all gears engage and the crankshaft spins smooth.
The clutch side was then assembled, sliding in the gear selector shaft and screwing in place the oil pump, followed by the primary gear and crankshaft mounted clutch. I left off the clutch cover so I could easily turn the crankshaft when setting up the cam timing. The barrels and head were fitted and the cam timing set to a 270/450 degree firing order. This makes firing pulses more even and puts less stress through the kick-start mechanism during starting.
The next thing I needed to do was modify the ignition system to run the additional cylinder. The standard Honda SS50 engine has a self-generating flywheel magneto ignition system utilising a single set of points. There was not
enough room to fit a second set of points and retain its magneto operation, so I removed the primary windings and condenser to make space, then made an adaptor plate to fit a second set of points at 90 degrees to the existing set of points. The sparks would now be generated by a battery and coil system initiated with the two sets of points, so I needed to upgrade the charging system with an increased output-charging coil.
The condensers were relocated ne ext to each of the ignition coils, wh hich was normal practice on m any Hondas of the era. With the ig gnition system modified, fitted an nd the timing set, I mounted the en ngine in my engine stand and fit tted the carbs and exhausts so I co ould test run the engine before fitting fi it into the bike. I had a s light problem to resolve first, th hough. I had bought a pair of Keihin K carbs at an auto jumble and a they were missing the t hrottle slides, but fortunately the needles n and clips were present. I had h looked for replacement slides, s but couldn’t find any so I thought: t “Why not make a pair?” I used a bit of 7075T6 aluminium bar, first turning the inside and outside diameters, then I drilled the central needle hole. I then ground up a special tool shaped like a parting-off tool, laying on its side, to cut the 1mm wide location slot by traversing the saddle back and forth indexing the cross slide 0.001 inches at a time until the slot was at full depth. The cutaway was then filed by hand until it looked about right. Last thing to do was to mill the angled slot for the idle screw on my milling machine.
The new throttle slides fitted perfectly so I connected the throttle cables and filled the carbs with petrol, connected up a battery, and within a couple of kicks it was running and sounded great. I ran the engine for a few minutes, checking for leaks, and was pleased to see there were none. To be sure, I ran it several times, gently revving to about half throttle and letting it cool down in between runs. The V-twin engine was starting first kick every time and ran sweetly with no abnormal noises or smoke, so it was ready to be fitted into the frame.
I built my first ever Honda SS100 V-twin engine on the Classic Motorcycle Mechanics stand at Stafford Show in October 1999. I then started it up for the first time in the centre of a large crowd outside the main entrance door. I was pleased and relieved when it started second kick and sounded great. A report of this show build was published in the May 2000 edition of CMM.