Derek Pickard explains how he built a very unusual classic trials bike in the 1980s, then sold it, and 20 years later bought it back to convert it for road use.
Story: Derek Pickard • Photos: Derek Pickard and Jim Scaysbrook
In the magic formula for motorcycle performance, weight is the one factor which plays a major part in the three most vital aspects of go, stop and turn. And it was achieving low weight which was a fundamental factor in the way I built a BSA 350-engined Greeves for classic trials back in the mid-1980s. The B40 Mk1 engine is the lightest of all the decent classic engines and the Greeves rolling chassis is as good as they come. With decent modifications to both I was totally confident of a top line classic trials bike that would plonk through the tightest turn and tip the scales at less than 230 pounds (105 kg).
It would have been nice to have started with a genuine Greeves trials rolling chassis but they proved impossible to find whereas Greeves motocross bikes with wrecked engines were obtainable – and some boasted the excellent Ceriani forks. Just for the record, nearly all classic Greeves frames have just the alloy beam at the front with the steel tubes for the rear. The engine bolts in place as a structural member at the bottom between the two, with or without a cradle. The top tube is cast into the head stem of the alloy part. Greeves frames are light, well made and good quality materials are used.
Converting for trials was as easy as repositioning the footpegs with foot controls to a more rearward position and bringing back the fork angle. The latter was as easy as heating the top tube and gently bending it back so the previous 32 degree angle is reduced to around 26. At the same time, the previously long 56 inch wheelbase is shortened to nearly 51 inches. Simple.
The resulting steepening of the fork angle raised the front of the bike which was easily matched at the rear with short spacers above the Girlings to achieve a more level bike with a decent ground clearance. The classic trials bike was beginning to take good shape.
Greeves were known for using two popular types of leading link forks: rubber springing with external damping and conventional coil over damper. Both follow the same layout where two large diameter downtubes end at the pivot point of the of the lower wrap-around link. The first type that goes back to the 1950s uses rubber bushes which not only pivot the suspension movement but also act as the spring. Tubular hydraulic dampers are fitted inside the main upright tubes. These look good and very classical but the problem is the lack of steering rigidity given by the large diameter rubbers bushes which are of fixed spring rate. So the Greeves upgrade in the late 1960s was to adapt the same basic leading link layout to conventional coil over damper motorcycle units which were fitted in front of curved main tubes to give a choice of easily changed spring and damping. All very good but definitely a little on the ugly side. For the struggling little Essex factory, buying Ceriani competition forks was a smart solution as well as an upgrade. This Italian front end may have been expensive, but Ceriani boasted excellent performance as well as giving instantly acceptable appearance compared to the oddball leading links to lessen Greeves’ freak factor. In choosing, my decision was to realise that Light-is-Right and so the Italian forks were fitted and on this road bike they work very well.
Why a B40?
This humble BSA engine is under-rated by many yet the basis of power for size is good. But it can only be taken seriously after improving a couple of weaknesses. It is one of the very few popular Brit classic engines which is an over-square short stroke which means the overall height is relatively low for a 350 single. That means it can fit under the low Greeves top tube which was configured for the low cylinder head clearance of a 250 two stroke.
Apart from the regular weakness of the bushed big end that is easily cured with an Alpha bearing, the only other bad marks are in the timing side to the gearbox where the mainshaft has only a bush for outer support and the lower layshaft/kickstart shaft has no oil seal. Whereas modern oils certainly cure most of any bush wear, an 0-ring must be fitted via a slot in the alloy case to restrict leaks from where the kickstart shaft emerges.
But at least this is a full 350 which means even in basic specification it will develop sufficient torque for decent performance and in a very light bike that should mean 500-type throttle response. When I was considering which engine to use all those years ago, much thought went into a B44 long stroke 440 which is a superb motor and the most under-rated of all Brit singles. But the total height of that lovely long stroke engine was a tad too much to fit under the top tube with the retention of a bracket for the all-important head steady/valve lifter cable, and have the top run of the chain clear the swingarm cross piece. Special building was never meant to be easy and compromise is often forced into many decisions.
Remember the rules
At this point, the basic rules of special-building should be stated. Obviously, it is no more than silly to attempt to nail a huge old Norton ES2 500 long stroke engine in a Bantam frame and some common sense must be applied. And apart from the physical size rule, the rest is all about making it work together. The rear chain must align and clear the tyre and top of the swingarm, the head must fit under the top tube, and the carb/exhaust should be able to be accommodated without tubular modifications. There is also the inevitable dilemma of how the controls rarely work out. This usual applies to the kickstart lever which does not clear the different frame’s footpeg and the re-arranging of the rear brake where invariably the compromise is to use a cable instead of a rod. More work.
But even after all the usual checks and guesses have been as to what engine will go into a frame, there is always an endless number of modifications. And nearly all of these require brackets, welding, further tweaks and re-routing. Projects always must allow at least three times the amount of time initially thought necessary.
B40 to trials power
Like all typically British engines of the early 1960s, the B40 engine is set up to deliver its best accelerative torque between about 3000 to 6000 revs. That may be fine for the road but it was all wrong for trials so the engine was modified for low down power and increased flywheel effect – but without adding weight.
A 22mm Amal Concentric carburetter was fitted and the 27mm port narrowed to 22m by the use of third generation two-pack epoxy putty, the compression lowered from 7:1 to 6.5:1 with a spacer at the base of the barrel, the flywheels rebalanced to a lower balance factor to suit the lower revs and the world’s mildest cam profile ground into the stock B40 cam. This was all complemented with the conversion to manual ignition timing by allowing the distributor behind the barrel to rotate through 15 degrees so the 30 degrees of flywheel timing variance could be controlled by a conventional handlebar lever.
This enabled the engine to not only start effortlessly but to develop its 3000 revs of most efficient torque from 1000 to 4000 and when pulled back on full ignition retard emit the most loveably flat big single sound.
The smallest engine and gearbox sprockets were fitted as was the gearbox internals swapped for those giving a wide ratio spread. With a big back sprocket, this set-up enabled the light bike to thump up the worst of hills.
The rest of the bike was all pretty easy really. The suspension settings at both ends were left alone, along with the wheels, brakes and tank/seat. The only hard job was squeezing in a Tiger Cub oil tank above the B40/44 stock off-road exhaust.
And that was it – a 230 pound purpose built thumper that was as light to push onto the trailer as to ride around the sections. It looked great, sounded superb and attracted attention everywhere.
But there was a huge flaw in my planning. I had not realised I was the world’s worst trials rider and how frustrating such a handicap was to be in an otherwise beautiful sport. What looks so easy can be incredibly hard. Frustration set it, family pressures could not be ignored and so the bike was sold. That was the right decision at the time.
Fast forward 20 years
After the children had grown, and a long period racing cars had worn off, my return to motorcycles saw me ride various machinery until one day I stumbled on this very machine. There it was, at the back of the garage of the man who had bought it from me a couple of decades previously. He had quickly learnt his limitations as a rider and after only a few rides abandoned the bike to his nicely garaged collection.
The temptation was too much. A price was agreed and the Greeves BSA 350 was soon back home where it had been built. That was a great feeling.
I could hardly wait. Within a couple of days I had flushed out the old petrol, cleaned the carb, checked there was still oil in the tank, a spark at the plug and – hey presto – within a few kicks it was thumping again. Examination revealed that not only did the oil tank anti-drain valve in the engine hold up for 20 years but the epoxy in the narrowed inlet port also did a good job in still being 100 percent effective.
Adding 20 years of normal body ageing onto what was previously no trials riding ability, clearly meant I could never ride the bike in classic trials again so the conversion began to put the special on the road. Although it seemed easy at the planning stage, the job took months and saw the weight rise from the previously good 230 pounds to 250.
The biggest job was arranging for a compact 12 volt battery to be held along with the switches and wiring to power the lights, turn indicators, stop light and horn. Off-setting the poof-teenth of weight that discarding the previous capacity discharge ignition system allowed all added up to sod-all. Road conversion always adds weight and I had to accept it.
Fortunately, a large capacity Greeves “desert” tank was found which dropped onto the stock frame mounts with the use of a super-beaut thick brown leather belt and buckle to hold it down. A lovely touch, everyone likes it. This 2 gallon tank is big enough for road use since the B40 engine pulling such a light bike is very economical.
New but period road tyres were fitted to the classic-section alloy rims. The off-road long Ceriani forks were easily converted for the road by pulling the legs up thru the triple clamps so the couple of inches above the top triple clamp where the tubes sticking out the top could then be used to locate Rickman-style clip-ons. Functional and neat.
The seat and trials-positioned foot pegs were left alone. A new chrome exhaust was bought and fitted. Also, all the fibre glass was freshly painted the correct shade British Racing Green – what else?
The low and wide ratio gearbox internals and sprockets were all converted to road type but initially the engine was left in its mid-1980s trials spec. This was done because of the loveable way the machine can pull-away in second gear and be in top within just a few yards. It thumped around town going around even tight corners in a retained high gear as the thump goes down to the slowest imaginable speed with the manual ignition pulled back to show off.
But true competition machines such as the Greeves not only have no provision for a stand of any kind but this chassis has no bottom tubes which means fitting a stand is extremely difficult. After a ridiculous amount of work and even more swearing, a 1970s Japanese trail bike side stand was welded onto the front left of the very strong box section swingarm.
Another disadvantage with a competition Greeves is that it has no speedo drive. Fortunately, one of those compact battery powered bicycle speedos can be used. Apart from that, I chose to buy two things from Indian ebay: the replica 150 mph Smiths chronometric speedo and the thick black leather tool wrap bag. Together they cost not more than the equivalent of a packet of biscuits and a piece of cheese – and were the only bargains I got while building the bike.
The 250 pound 350 cc was put on the road as an easy-to-start and ride bike which the light weight allowed good acceleration and braking. Although it is very much a later type of big single, the total engine conversion made it thump and behave like an earlier generation of longer stroke British single. I really would pull away in second and shift to fourth nearly immediately.
The combination of low gearing and trials type engine meant the speed was mild, very mild. In top gear, a quarter throttle gave just 30 mph and half throttle up to 45 mph. There was no more speed; not downhill, not with a tail wind, not at any time.
You see, the only disadvantage of this loveably gentle low down thumping engine was the lack of top end performance. The incredibly mild trials cam meant the engine simply refused to open out past 4000. Not matter how steep the long down hill, this bike simply would not exceed 45 mph. Around town, that is no problem, but on the open road the bike was left behind by everyone but BSA 125 Bantams.
Ride comfort was good and handling was no less than very good due to the lack of speed. The same could be said of the braking. This bike retained the 6 inch British Hub Company (BHC) front brake in its 21 inch off-road wheel which with an Avon Speedmaster tyre proved surprisingly good, however it looked a little weird; but most of this bike is very different anyway.
One little by-product of the restricted revs was the way the 4000 limit serves to prevent the engine going faster and incurring inevitable harsh single vibrations. Also the combination of two cush drives from the BSA clutch and BHC rear hub means the transmission is incredibly smooth, even when making clutchless gear changes. This was a true sweetie and best used around town or at the most in pleasant rides around winding hills.
So this Greeves 350 BSA was put to work as a strictly a suburban odd-ball classic. With one thing for definite: whereever this bike was ridden it became an attention-getter like all specials. When a million-dollar restored BSA 650 Lightning is parked and this bike pulls alongside, bystanders immediately switch their gaze. All enthusiasts want to eye-ball the thing and work out what’s what and how they would’ve done it, always offering advice on improvements. It’s incredible that when it comes to specials, everyone’s an expert.
Then came the future
The more I rode the bike, the faster I wanted to go and more frustrated I became with the absence of any top end engine power. Although what felt like 12 bhp was okay for 250 pounds around town, returning the engine to stock output would give the option of out-of-town riding.
So a stock cam and followers were installed along with the larger size carb and the inlet port reopened. The ignition and exhaust were not touched. Then it all came alive. A stock B40 in a 250 pounds bike can accelerate like mild 500.
I always love using the manual ignition control. The way the exhaust note can be made to sound flat when thumping along the road is superb and the only downside is excess blueing of the exhaust pipe.
Now it revs out past its previous top end and feels really good on 50 mph winding roads. But – and this is typical for a special – another difficulty has emerged which requires work; the overall gearing is still too low. So a smaller rear wheels sprocket is the next mod as the present gearbox sprocket is the biggest available for the B40.
The only other problem so far has been sitting on an open road for longer periods during the summer results in the temperature in the small capacity oil tank getting too high so forcing long coffee stops. Maybe I should look to fitting a bigger oil tank or converting the present one for more capacity by welding in a box-like addition on the inner side. Then again, maybe I should enjoy the extra coffee.
But no special is ever perfect or finished; there’s always more to be done. A year after first putting the once trials-right bike on the road there’s still a bit of conversion work to do. Specials are special that way.