Jumbo training
The Spanish industry was out and the trials world had gone Italian by the 1980s.
Bigger was supposedly better. Enter the Jumbo, or TL350, or Schreiber’s works machine, which shows a few development ideas to make the big bike more rideable.
As reigning world champion Bernie Schreiber should have been focused on retaining his world championship in 1980. Had the Bultaco factory been able to capitalise on his success, that is precisely the way things would have worked out. Unfortunately, the industrial climate in Spain at the time meant instead of getting as many Schreiber Replica Bultacos as possible out into the trials world, the factory could barely produce a machine of any sort, let alone fund a comprehensive world team.
Bultaco’s team riders were obliged to look elsewhere and some hard decisions had to be made while the factory tried to sort things out. Ultimately they did manage a small scale return to production but it was pretty much the end of the line for them.
However, this didn’t help Bernie at the time, his
options being limited to carrying on with his Bultaco – which he did for a while.
But without factory backing, attacking a world championship isn’t easy. The American champ was in the top 10 effectively as a privateer, and even won a couple of trials. The dilemma was to carry on with no expenses or salary on a bike he knew and liked – there wasn’t another one available to give him – or take up some offers.
Italian maker SWM made an offer for him to carry on with the Bultaco for 1980 then go yellow for 1981. In retrospect this is an offer the Californian feels he should have taken as it might have meant a second and even third championship. In the end he went to another Italian factory called Italjet, who were rumoured to be buying Bultaco out. In this contract he would be carrying on with a machine he was familiar with, indeed Italjet had a Bultaco finished in their green colour and a promise of better to come.
Sadly this didn’t come to fruition as Bernie found himself as development rider, a role he has never claimed to be able to do. Discussing this in our feature in issue 47 he told us: “I know when the bike is right and how it feels... but to radically alter it and develop it? Well that’s not me. I thought Manuel Soler would be along in the Italjet team too, but in the end he went to Montesa.” Despite the uncertainty Schreiber still finished second in the world and had he not missed a couple of rounds could well have won the title again. Things were promising but the factory produced a new model which was wrong for Bernie’s style... and 1981 is best glossed over. The offer to go SWM came up again and this time Bernie took it.
As part of a team and not expected to be the sole development rider Bernie could concentrate on riding, and while he didn’t win the championship he did win the Scottish Six Days Trial which attracted the world’s top riders in those days.
On signing with SWM Bernie was issued a TL320 model – actually he would have several machines a season but they would be 320s – and this is a model he felt was his favourite SWM. The call for bigger engines came from Martin Lampkin, a rider with a particularly forceful style who had made the same call at Bultaco. The challenge for SWM was to make a motorcycle which suited not only Martin’s style but the other team riders and the buying public too. This is the role of the development riders…
In 1978 Charles Coutard had been engaged by SWM to develop a trials machine based on the Rotax
Bombardier engine. Effectively heralding in a new era to the sport, this new manufacturer had brought some fresh thinking to old problems and in Coutard had got a rider able to bring results and ensure the production bike would benefit.
Weighing in at 187lb the prototype was light enough and followed modern thinking by having the swinging arm spindle pivoting close to the gearbox mainshaft, giving the rear chain an easier life and less snatching, which helped grip. Further smoothing transmission was a transmission shock absorber, similar to the one used on the SWM enduro models.
The model being tested for the feature was Coutard’s own hard-used test bed and at the time of the test two new models were on their way to the French champion.
He allowed several areas were being attended to for the newer machines – power, for instance, was reckoned to be too sharp for trials, a redesigned disc was made and the new part would be in the engines. Clutch action was deemed light – the engine could be started in gear too – however, gear changing was reckoned to be difficult so a new selector was designed.
Coming in for praise were the spread of gear ratios – all six of the blighters – which gave more choice for sections. The test rider tackled a typical section in first gear and failed miserably (his words), but doing the same in second was more successful… while third gear was even better. Coutard tackled the section in fourth on tickover… truly the world was changing.
Along with these new engine characteristics came a new riding style to match them and 1979’s world trials champion had demonstrated his skill in this new way. Now, it bears saying here the old guard laid the blame for changing trials firmly at Bernie Schreiber’s feet – firmly on the rests they may be – but as the lad said to us in issue 47 “… I never set out to change trials but did set out to change the way I rode within the rules as they existed at the time…”
As 1983 dawned Bernie was riding one of the new 350TL models, which by then had been named ‘Jumbo’, and he was destined to give the new machine its first serious win by topping the entry in the Spanish world round. These engines were different to the disc valvers which had gone before as the induction system was direct into the crank case through a reed valve block and had required a new frame and cycle parts to house it. It did outwardly resemble the 320 machines though and was the same ellow and blue colour scheme.
It was an excellent debut and showed the world that Schreiber was still a force to be reckoned with, despite
WHITE ELEPHANT
On the eve of Bernie’s 1982 SSDT win – when he was still in the ‘might be his year’ category – The Motorcycle carried a news report of the prototype, referred to as the ‘progressive power’ model and the headlined screamed ‘…SWM no one wants… ’to be fair to the team riders and the factory, riding a machine in a six-day trial when it had only been finished a few days before was probably not the best idea, but it caused a stir in the paddock. The few details available were a tantalising taste of the future, a capacity of 348.5cc from a bore and stroke of 82mm x 62mm, actual power was on the secret list though. Export manager Massimo Levi, who brought the bike to Scotland, told Motorcycle’s man a prototype with a plastic engine had been built earlier in the year and Martin Lampkin had popped over to the factory to try it out. Feedback was positive and five alloy engine prototypes were put in production, the one in Scotland was the first finished. Bernie got the final comment in the piece when he claimed the power would be more like a Bultaco. being probably the oldest rider at the sharp end of the competition. He remained in the top three for three more years, but SWM too succumbed to financial pressure and closed its doors.
This Jumbo…
Now, given the way the works teams did things in those days an ex-schreiber machine isn’t ultra-rare. There aren’t hundreds of them, but they are around and pretty well known.
My first question to Stu Clements about his genuine Schreiber Jumbo was how did he get a hold of it? “It was advertised on an internet auction site and wasn’t a lot of money, in fact it cost more to get it over here from the USA that it did to buy it,” the oil rig commissioning engineer told me as he shifted the bike a few millimetres this way and that to get the light and angles right for our pics.
What Stu bought was a well used 1983 machine which Bernie would have ridden in the USA. Once he was finished with the bike it was moved on to a friend of his, then sold to a car dealer who rode it a little, then it languished for a while before being sold… to Stu. It seems almost incomprehensible such a bike should have fallen into disuse but at that time nearly 20 years ago Bernie was not as active in the scene as he is these days – not exactly the forgotten champ, more the champ in the background. Still he’s back on the scene and trials is better for it.
The world of old motorcycles is a funny old place and sometimes what is shown isn’t always what it seems, and typically with anything likely to be famous it is all about the provenance. With this machine came an incredible amount of documentation and we can joke by saying even the family of the lad who brought the washers to the bench where the bike was built at the factory is named, so detailed is this provenance. Suffice to say there is no doubt about the heritage of the machine.
This does cause a problem though, how far do you restore such a machine? Sometimes there is little option but do everything, other times the patina of age is best left alone. My own feeling is if the bike is useable and clean then its battle scars are badges of honour. There!
Taking on a bike which used to be a cossetted works machine then has been out in the privateer world can be a daunting task… for instance, has it been looked after or abused? Is it as it should be or has it been altered again? The uncertainty is nerve-wracking.
In the end, Stu got one of those nice surprises which always seem to happen to other people. Yes, the bike had been used, but internally it was quite sound and the compression was so good it managed to break a kickstart shaft in a trial. This meant the engine had to come apart, as there’s no way to change the shaft without splitting the cases. Before that, and during the initial rides, Stu found the power to be quite different
to other Jumbos he’s ridden. “To be honest, the Jumbo is virtually un-trialable in standard form, it is a wheelie machine…” Such a power delivery may have suited Martin Lampkin but not other riders, and something was done at the factory to calm things down a bit.
What Stu found when splitting the cases was the reed valve had been taken out and the hole filled up with two-part epoxy metal. The carburettor – a 30mm instrument – now feeds fuel into the back of the engine in a more conventional way. Clearly the factory had become aware of power issues. Stu says there is an official document out there which details this mod but it did make life interesting when splitting the cases.
“I had to cut the epoxy metal with a wood chisel!” he says. Once the kickstart shaft was changed the engine went back together and since then all has been okay.
Difference is in the detail
Delving in to the engine revealed not only the reed valve modifications but convinced Stu this must have been a development model as later Jumbos have the hole blocked off with a plate.
Allied to the inlet mods is a much bigger carburettor, 30mm choke instead of 28mm, which rather obviously sucks more air in than a smaller one. To provide this extra air the airbox has been increased in size and has a modified lid to allow more air in and keep muck out. This did have an effect on the low down end of the carburetion, so a special needle jet was made to allow a rider to trickle along on minimal throttle without the engine gassing up. SWM did the same exhaust mod to their front pipe as Bultaco had on their works models and there is extra length welded in.
Doing this smooths the power right through the rev range and gives much more toque to the engine while still allowing it to supply instant power when the throttle is snapped open for those big steps starting to come in to world trials. There were other modifications to the exhaust too, with the middle and back boxes showing evidence of work. The middle box had a heat shield on it when Stu got the bike too. At the time he thought maybe the bike had been used for trail riding.
The science of two-stroke engines had, by the Eighties, become more understood with the exhaust lengths, back pressure in silencers, engine breathing and swirl in the cylinder heads all combining to produce the required power for a particular application. So, for a team bike trying a different
combustion chamber shape is worth doing and on this Jumbo there is a cursive ‘S’ etched into the head, and it has been suggested to Stu it could be Pietro Sironi’s ‘signature’. Sironi was one of SWM’S founders. Maybe Bernie knows if the man would ‘sign’ factory bikes?
As the season went on modifications would appear as needed or preferred by the rider – this is not exclusive to works teams as we all do similar things, it’s just a works team is better at it. There are additions such as steel guards around the engine cases – imagine the embarrassment caused if your team man fails to finish because a case was cracked on a rock? Braking was beginning to be more important to a trials rider, okay it’s always been good to stop but as the rules allowed such stopping and balancing in sections a rider wanted to be able to stop exactly where they wanted, disc brakes these days ensure that will happen but drums need attention to work that well. On the rear brake the actuating arm was extended for more feel as locking up under ssure from a trials boot was just as embarrassing as not stopping. Up at the front to make the cable action better the arm was cut and re-welded into a different shape.
Probably more personal is the mod to the steering head. Bernie, being quite tall, has his bars forward and the top yoke has been cut and welded to move the clamping position more central. The subject of handlebars is interesting and alloy Renthal bars were available during this time, but Bernie is on record as preferring steel bars because they don’t flex as much. Don’t forget, originally Renthals didn’t have the cross brace, which wasn’t a problem for low bars but higher ones could flex. Additionally the forks are further through the yokes. Inside the forks, which are Betor for the Jumbo, Stu found a pre-loader spacer made from copper.
Initially the SWM wore long travel Girling shocks on the rear but these were past saving and instead Stu has Falcon shocks. It is likely the longer travel is to match up with the extended fork length because the stanchions are through the yokes a bit more. This keeps the ride and steering angles the same.
Trimming the front mudguard might seem a simple thing with no real value, but it helps the rider see the tyre and what it’s doing, plus the exhaust mods could mean it would catch the front guard and trimming it just prevents that.
As we looked over the SWM, Stu thought about what was different to the standard model and reckoned he’s pretty much covered everything except the beefed-up front engine mounts welded to the frame and the rubber buffers fitted between the fins to deaden ‘fin-ring’, which can make engines sound odd, esp iall lar e cap two-strokes.
There’s nothing too technical on these sound deadeners, they aren’t a special rubber with acoustic qualities, they just look like sections of fuel hose.
So that’s it, the works Jumbo fettled for a rider at the top of his game... but having had a wobble on it at Alvie during the Schreiber Trials School it seems a much better bet than the folklore surrounding the standard machine.
I've not ridden the reed-valved standard one so can’t comment, though I can surmise or assume it would be too sharp a power delivery for me too.