THE FINAL BIKE
We all recall the first bike we owned and rode. Roy Cross has built something a bit different – his last bike, the culmination of 60 years of experience with Vincent motorcycles. Is this the ultimate featherbed V-twin special?
This project started in the paddock at Brands Hatch in the 1950s. The travelling marshal was riding a hybrid that was quite new to us all: a Manx Norton with a Vincent engine. That has got to be the ultimate bike – the grunt of the Vincent with Manx Norton handling. Experience later told me that this is not necessarily so… In 1958 I bought a basket case Black Shadow as individual components. I sold the cycle parts, put all the engine bits in boxes and took them to Jim Smith, the renowned builder of Vincent and Manx Norton motors. He built a motor with 9:1 pistons, new big end and main bearings, Mk2 (Black Lightning) cams, GP carbs with ports opened out and a larger inlet valve. But the demands of a growing business left no time for diversions so the engine went under the bench and there it was to stay until I had time.
In 1965, shocked by the death of my first wife, I concluded that there never would be time unless I changed my priorities and made time. I blew the dust off the Shadow engine and, with difficulty, fitted it into a Manx Norton chassis. But the engine was too high and too far back; impossible to do any work on the top end. One of the reasons that the Featherbed Manx handles so well is the weight distribution. The Manx crankcase is sufficiently narrow to drop between the lower frame rails, which brings the mainshaft level with the wheel spindles. So I extracted the Vincent engine again, took the plugs out, squirted some oil down the bores and laid it against the workshop wall to await a decision. There it stayed for 35 years: you can’t rush us old craftsmen.
In 1999, age 74, I sold my business and commenced the holiday of a lifetime. I was finally able to restore the bikes I had acquired over the past 50 years. I did my Black Prince first, then a 1949 Rapide. In 1965 I’d bought a Black Knight chassis for the princely sum of £30. In the early 90s I bought a Comet engine
and gearbox, with the idea of mating them with the Knight to produce a replica Victor. The Victor was the enclosed version of the 500 Comet. However, I encountered lots of problems. The singles’ wheelbase is ¾” shorter than the twins’ and nothing fitted, so the project was abandoned and the two bikes rebuilt back to their original configuration.
I never lost my hankering for a Norton / Vincent hybrid. I realised that the answer was to use the engine as Phillip Vincent intended and as Phil Irving had designed it: as a stressed member. Anything bolted solidly to that 150lb lump wasn’t going to move. Logically, the answer was to situate the engine where it gave the best weight distribution and remove any frame tubes that got in the way. But I couldn’t bring myself to do that to a Manx frame.
Then I came across an unfinished race project. It had started life as a Dominator, then raced with a 750 Atlas engine. When I bought it the bike was powered by a Model 50 engine. A buyer came along for that engine and the rest was put aside.
At this point I should introduce Young Len. He came to work for me as a sixteen year-old, shortly after we started our business. He was a born, instinctive engineer. I taught him the first principles and they stuck. If you fully understand the first principles, logic, talent and experience does the rest. He stayed with me until he got a job with someone who could pay him what he was worth. We never lost touch and in retirement he moved to the next village. He finally got the Norvin project moving by explaining that if I didn’t get off my arse and get started then I was unlikely to finis h it – let alone still be alive to ride it. So we started. I had a pretty clear vision of what I wanted. It wasn’t going to be a café racer: clip-ons and rearsets don’t suit geriatrics. The finished bike should not weigh more than 400lb so anything that could be made in aluminium alloy would be. If not, it would be made in stainless unless it had to be welded. I have long felt that bikes are too heavy, modern ones ridiculously so. This seems to point to incompetent designers. Good suspension and roadholding are dependant largely on the ratio of sprung : unsprung weight. It seems that they achieve an acceptable ratio by loading up the sprung weight.
Our first task was to strip the donor bike down to the bare frame. I wanted to fit taper roller bearings to the steering head so removed the cups and cones. The bearing houses were distorted from weld shrinkage during original manufacture. This doesn’t much matter with cups and cones but is not acceptable for taper rollers. So whilst Len turned up a screwed mandrel, I attacked the housings with rotary files until the outer bearing tracks would drop in with about 4 thou’ clearance. The mandrel was used to locate the bearings in position and Loctite bearing-fit dribbled around the gap where it was drawn in by capillary action.
We left this overnight to set and the next day I cut the redundant frame tubes just under the steering head and in front of the swinging arm gusset. Len turned a metre length of round bar to fit into the steering head bearings. We stretched a piece of cord along the work bench and with a spray can marked a datum centre line. We set the frame on the bench with the metre-long mandrel through the head bearings and a rod through the swinging arm mounting holes. The alignment was then checked with a spirit level and plumb bob. There was a little twist, but nothing that a big welding jet and brute force couldn’t correct.
Using bits of rope, wedges, packing pieces and lots of ingenuity, Len mounted the
inverted frame on the turret mill overhanging the front, and set level with a spirit level. Using a rod through the swinging arm mounting holes he machined the ends of the cut tubes, providi■g me with an accurate face to which I would bronze weld the front engine mounting bracket.
I stripped the engine and rebuilt it as an empty shell so that it was light enough to ha■dle. The drive side of the Vincent engine is on the right, so I fitted the swinging arm i■verted and set to measuring where the e■gi■e would need to go laterally to get the sprockets in line without the rear chain fouling a■ anything. The engine needed to be displaced to the left by just under half an inch.
I then took to the drawing board to desig■ a twin-disc front hub. This was quite straightforward. I had previously fitted discs to my four Vincents and merely changed the dimr ensions for the different fork width and spi■dle size. The problem in fitting discs to spoked wheels is one of space. Calipers with cast bodies won’t fit between the spokes and fork le~gs so they have to be machined from solid.
I went to Chris who owns Pretech in Reading, a billet machining specialist who made my Vincent calipers. He’d recently made a small batch of Norton fork sliders for another client, with caliper mounts at the back. Standard Nortons only use single discs, and I like to spread the braking loads over both legs.
Next we needed to determine the position of the engine. For this we needed the front wheel position, which needed the forks. The donor forks had some very nice alloy yokes which we decided to use, along with the damper units. Everything else was replaced. We used EBC 300mm floating discs, the same as I had used on my Vincents and whilst Young Len was machining all the bits for the front hub, I assembled the forks. The damper units were modified to correct a well-known fault of Roadholders which permits a mechanical stop at full compression rather than an hydraulic stop. This well-documented modification involves blanking off the holes in the shuttle valve, and re-drilling them higher up.
I assembled the hub and built it into an 18” alloy rim with stainless spokes. Len took my drawings and went to work on the swinging arm pivot bearings. He turned and fitted new bronze bushes and spindles with end caps that were a tight fit between the gusset plates, bearing on O-rings in the ends of the bushes that produced an oil-tight assembly allowing the space in the cross between the bushes to be filled with oil for lubrication.
The donor bike came with a nice alloy cone hub at the rear, which I laced into another 18” alloy rim. We made some dummy struts to position the swinging arm. We then fitted the forks and the wheels, fitted a minimal Manx front mudguard and mounted the bike on the bench, aligned with the centre line and held vertically with cargo straps. Now we could select the position for the motor.
Firstly there was the ground clearance. Whilst we were unlikely to be investigating the limits of tyre adhesion, we had to provide for riders younger and less inhibited. We were using Vincent folding footrests, so I decided that they should touch at about 45 degrees and lift a bit further before the clutch cover grounded. We packed the motor to this height
and moved it as far forward as it could go. At that position the front mudguard would just touch the exhaust pipe if the forks were fully depressed with the steering turned to the left.
We set to with cardboard and scissors and roughed out a template for the mounting plate for the drive side. The Vincent motor has a 5/16” alloy plate which bolts to the outer face of the gearbox and carries the gearchange mechanism, kickstart assembly and the footrests. If a Grosset starter is fitted, this plate is replaced by one extended at the bottom to mount the starter motor.
We made a dummy plate from 8mm MDF which carried this lower extension but continued rearwards to the rear gusset plates, and drilled our dummy plate to match with the motor. We took that dummy plate to Trevor Southwell, the English end of the Grosset organisation who supplies Francois with most of his hardware. We ordered a starter kit from Trevor, but with a replacement alloy plate like our template.
The drive side engine plate arrived from Trevor and, with this fastened to the crankcase, we positioned the engine under the frame. Len machined the alloy cylinder head brackets and I made the steel fabrication that connects the front of the engine to the frame. With Len’s brackets in position and my forward bracket fitted to it with a fitted dowel, it was tack-welded to the frame. I then transferred the two mounting holes in the gusset plate into the alloy engine plate and Len turned two fitted bolts to suit.
The mounting plate for the other side was machined from ¾” alloy plate, stepped down to 3/8” on opposite sides and ends to match up with the offset to the gusset plate. Again two fitted bolts were used.
Things now proceeded steadily. The rear head bracket was connected to the upper frame tubes with a mounting that holds the engine rigid in the lateral plane, but permits it to move in all other directions to allow for growth of the motor when hot. We connected the swinging arm to the upper shock mountings in the loaded position with dummy struts, put bathroom scales under the rear wheel and noted the weight with Len seated in a riding position. This figure combined with the desired length meant new shocks arrived the next day. It was now time to reassemble the motor.
When Vincents were still being built at Stevenage they took great care with their crank assemblies. The works specification called for the whole crank assembly to be concentric within 2 thou’ (.002”) total indicator reading. There’s a very good reason for this. The Vincent crankcase is a stressed, load-carrying component and will not flex like the average crankcase. It also has two bearings either side. Any eccentricity in the crank will walk the bearings out of the housings until they foul the big end nuts. A new Vincent was vibration-free right through the rev range. 70 years later, only expertly-rebuilt motors achieve this ideal
condition. My crank assembly was outside these limits: 0.002” on one side and 0.005”on the other. So I split the flywheels and the unused crankpin came out much too easily.
I phoned Bob at Alpha Bearings, asking him to supply a new big end assembly with oversize ends, and asked what interference he recommended. He enquired how I planned to bore out the flywheels. I’d intended to do it on my turret mill; the same way Vincent had done. He suggested that I might prefer to let them have the lot and they would do it on their jig grinder, so that’s what we did. We collected it three weeks later and when I checked them on my balancing rig they were perfect.
I now finished the welds which had been tacked on the various bosses and lugs as Len had made them. We made and fitted a tread-down centrestand and a prop stand. Since the swinging arm had been reversed, the mountings for the tops of the suspension units were no longer in line and had to be replaced. An alloy bridge piece was made to connect the rear mudguard to the frame and the GRP oil tank. It was hung from its top with a flexible mounting with a battery tray bonded to it. Before fitting the mudguard I had a GRP moulding taken from it and this was bonded into the back of the tank, allowing the tank to rest against the mudguard with sponge rubber between.
We were ready to install the engine unit. Len made stainless dowels with threaded holes to connect the head brackets to the frame with a light interference fit. The threads meant a puller could be used to fit them. The four fitted bolts went in at the rear, and the GP carbs were fitted and mountings arranged for the matchbox float chambers. GP carbs have no idle circuit, so I drilled the slides to take 6BA grub screws so that we had adjustable throttle stops. This gave us a rather fast tickover, but would prevent me losing the engine in traffic.
A tubular framework carried a fairing which Sprint Equipment supplied. Vincent-style bars were bent from polished stainless tubing and mounted in trunnions on the tops of the fork legs, and an instrument panel mounted on the tops of the trunnion caps. The control levers were fitted to the bars and we turned our attention to the front brake, using the same arrangement that had worked well on the Vincents. A Bowden cable went from the brake lever to a box under the steering head. It operated a pull-type AP Racing master cylinder via a bell crank that gave a 2:1 mechanical advantage. Braided hoses connected to the calipers and a pressure switch for the brake light. A reservoir was mounted in the instrument panel for the brake fluid.
The oil pipes were plumbed in. Fuel pipes arranged and the controls connected. Enough electrics were installed to provide for the minimum needs of the engine and then it was time to fire it up…
Using an electric paddock starter, it fired up straight away. The carb settings, done by Jim Smith all those years ago, seemed to be about
right. We had an acceptable if a trifle fast idle setting. The next stage was to load it on the trailer and take it to an airfield, to see if everything worked.
This time it was reluctant to start either by kickstart or the Grosset starter, but eventually it did. We had the place to ourselves. We took it in turns to ride the Norvin around the perimeter track and were very pleased with the result. The only fault we found was that the Sprint fairing was bobbing up and down on its mounting, which obviously required stabilising.
Back in the workshop we beefed up the fairing mount. We carefully checked that there was no more welding needed before stripping it down and sending the bits away for painting and powder-coating.
The bits came back commendably quickly and we proceeded to join them back together.
This all went smoothly, largely because we never had to stop and think which bits went where, and the ease of access became apparent when installing the engine. It merely required jacking into position under the frame, fitting the two dowel pins at the top and the four bolts at the rear and the job was done. It took about twenty minutes.
Over Christmas I attacked the electrics. A Smiths magnetic speedo went into the place provided in the fairing. A small nylon boss, carrying a small magnet, was clipped and superglued to the alloy rim with a sensor fitted into a housing at the back of the fork slider. This sensor could be withdrawn to clear the tyre if the wheel was removed. With the speedo in the fairing I had an instrument panel with room for a car-type key switch for ignition and starter, an ammeter, a meter to show battery state, individual switches for the lights, and indicator lights for high beam, ignition and indicators. The wires to the headlight passed through a lug and socket whilst a similar plug and socket went in the lines to the speedo. For ease of maintenance a mating plug and socket went on the ends of an extension cable. This enabled the fairing to be removed to get access to the wiring which would normally be contained within the fairing, but still remain connected to the bike.
Come the New Year, the bike was ready for the road. When Jim Smith originally built this motor he had bored and honed the new cylinders to a thou’ oversize, presumably in deference to youthful exuberance and hard-alloy Specialoid pistons. Now, with modern low expansion pistons we had none of the usual stiffness of a rebuilt engine. I insured it and took it off SORN and we were ready to go.
Len took it around the lanes first and returned wearing a big grin. ‘What’s it like?’ I asked.
‘Just try it,’ he replied, so I did. It was better than I could have hoped for. It was a joy to be aboard. On a B-road with a series of S-bends and a surface that’s in need of attention the bike performed so well and it was so comfortable. It was so rewarding of our efforts. Tweak the throttle and hold on tight because it went like stink. But – there’s always a but – on any sort of trailing throttle it was like a Chinese new year. Because we had set it up to idle without an idle circuit, on the over-run unburned fuel was collecting in the Gold Star silencer where it ignited. It sounded like a terrorist attack.
What to do? We swapped the camshafts for Mark 3 touring cams to see if less overlap and less valve opening would improve matters. It did, but only a little. We had to face the fact that ultimate performance was academic. The GP carbs came off and a pair of Mk2 Concentrics went on in their place. As the Concentrics have integral float bowls it also provided more room for the reduced amount of plumbing.
At last it was done. I was able to ride my dream bike on my 90th birthday, and very satisfying it was too.
But time waits for no man, tempus continues to fugit and here we are six years later. Young Len died last June and I haven’t ridden for three years. But I’ve no complaints. I rode for nearly seven decades. I’ve borne a charmed life and it’s mostly been fun. Nothing lasts for ever. If I’d known I was going to last so long, then I would have taken better care of myself!