In the mid 80s, biking hadn’t quite decided what worked best and the end result was a host of gimmicks, acronyms, initialisms and other such foibles. This Dresda Yamaha plays host to one of the worst ideas to date, the turbo.
The wrapping of the diminutive Yam engine in a hand built Brit chassis is decision verging on genius. The basic concept of the XJ550 was a good one, create a lightweight, mid capacity four, and give it a similar performance to the benchmark RD350LC, while using considerable less fuel in the process. The end result was a cracking little, environmentally friendly, bike, which quickly attracted a strong following, but in the cold light of day was left sadly lacking in the handling stakes. As this example was badly damaged in a road accident it made perfect sense to throw away the bits that didn’t quite work well, and replace them with new parts that do.
The Dresda Yamaha sits up pert and paying attention, head held aloft like a race horse ready to run the national; the head angle is steeper than the standard 27 degrees of the XJ chassis, and this in turn gives the turbo a real sense of quick handling especially dropping into tight bends. The Marzocchi remote-reservoir rear shocks out perform the Yam units by a huge margin, the originals always feeling under sprung and under damped too, while the Latin dampers handle all that is thrown at them and more, particularly as they now get to team up with a sturdy box section swing arm. The rest of the cycle parts are left wanting, the original XJ sported little more that a RD350LC front end, albeit with a 19-inch wheel, which barely worked on the former machine so by adding an extra 40 kilos, the bouncy bits and stoppers up front are struggling to keep it all in check. Add into the equation the extra 30mph that the turbo can achieve at the top end and the brakes really do start to look pitiful. Thankfully, they do work, and at low speed very well, but their power diminishes exponentially as the speedo winds its way around to the dusty end, and great forward thinking is needed to haul this machine up in good time.
The 550 Dresda chassis is a complete one off, built especially for this project and, as such, no others exist. It is based largely upon the Dresda Solitaire range of frames, originally designed for the CB900 and GS1000 fours, and really should be sporting an angular, twin headlight fairing. Thankfully the extra weight that this would bring hasn’t been rested upon the already heavy-laden Yamaha middleweight and currently the bike runs without such encumbrance. The tube work has been arranged in such a way as to allow the engine to sit lower within the chassis, this is achieved by removing the conventional lower frame rails and allowing them to run around the periphery of the engine casings. The top rails splay out from the headstock and everywhere, and from every angle you care to look from, the tubes meet in the classic triangle formation for massive strength. The end result is a sturdy look that, as an added bonus, has built in crash bars, but the riding position does become a little tiring after a short while. The seat is a good deal lower than the 790mm of the XJ, and the rear set footrest place all the riders weight on the wrist areas, added to this, the extreme heat that is felt from the exhaust mounted high up on the left hand side and it soon becomes a hostile environment, especially for the inner thigh on that side.
Despite there being a pair of pillion rests fitted to the huge alloy plates that hold the riders controls, the seat is definitely made for one and a half, ideally the spare bit of seat is to used to sprawl out of the way of the wind blast that will be all too evident at the 140mph plus that the turbo makes this Yam capable of. In use the superb XJ is effectively ruined by the addition of the turbo, the smooth midrange and excellent fuelling, something that Yamaha had made their own throughout the 70s is consigned to the rubbish bin leaving a vast hole where there used to be usable mid power. Then all of a sudden the turbo awakes, the exhaust gases having spun the turbines up to near on a quarter of a million revs per minute, and the pressure within the intake manifold becomes such that the engine has to give in and allow itself to become swept along in the rush. It’s a bit like an over tuned two stroke, all or nothing, and certainly not what is required for safe or fun road use. The power delivery would be great in private, say with a couple of miles of empty runway ahead of you, but not in the company of other road users and road side furniture, and definitely not for the faint of heart in either case. There is also a noticeable lag between the time any throttle is added, and the moment when the engine reacts, this can be disconcerting especially mid corner as the, usually rock steady, Dresda tubes take a dislike to this sort of behaviour. One minute you have 50 or so gee gees to play with, and the next a good deal more on tap, and with little or no welcoming introduction. The turbo liberates around 30bhp more on tap at full chat, with a similar increase in torque to match it, but it comes to the party with a great bang when it finally arrives, so not a good idea to be adding full throttle at full lean, or mid corner.
Take the turbo off and you will have a sweet machine that looks almost as special, handles well, and you wont burn your legs in the process. Of course leave it on and just enjoy the rush, but do be careful where you unleash it.
Turbos… blowing in the wind
They came and went in a flash, the darling of the early 80s turbo motorcycles were an instant hit with the technophobes, but in real life few could really enjoy the huge rush and peaky power. Honda became the first to put such a machine into production, with the strange choice of turbo equipped CX500, a “commuter” machine reputedly designed from the outset to be a turbo, making it the only liquid cooled turbo of the period, while other Japanese manufacturers adapted existing air-cooled designs to demonstrate how well the new technology didn’t work.
In a normally aspirated engine, the down draught of the piston sucks the next charge of air and fuel into the combustion chamber. A turbo works by compressing the air that is fed to the inlet tracts and, as this means more fuel can now be added to the mix, forcing a larger amount of this combination into the cylinders with every induction stroke.
The turbo is basically a pump split in two halves. The “hot” end spins, utilizing the exhaust gas pressure, at speeds up to 200,000rpm, and beyond is some cases; the combination of the exhaust like heat, and extreme speeds leads to some very high temperatures within the turbo unit and is the main cause of failures. Of course it’s a bit of a chicken and egg situation, as the turbo needs the engine to be revving highly to provide the pressure to get it revving higher still, hence the designs unsuitability in a road or race situation, and the feel of considerable lag between opening the taps and anything significant actually happening.
Thankfully it was a passing phase in motorcycling history, fondly remembered by those who never sampled one, and viewed as machinery best kept in a straight line by those who did.
The XJ550 first seen in 1981 was Yamahas hi tech answer to the fast emerging middleweight sector of the late 70s and early 80s. The engine was a scaled up version of the Japanese market only XJ400, and also based heavily upon the thinking behind the XJ650, launched in 1980. It was also the first European model to feature the YICS (Yamaha Induction Control System). The YICS, basically a system of passages that link each of the four inlet tracts, was developed at Queens university Belfast, and was implemented to smooth out the mid range. How well it worked is arguable, as other engines without the system appeared to work equally as well, making it one of many 80s acronym gimmicks, and as the miles rolled over on the speedo, the YICS equipped engines became more difficult to keep in tune, especially at tick over when many would hunt and eventually stop if left for any time.
Deeper inside the XJ mill, and the top end is fed by a pair of camshafts operating a quartet of valves for each cylinder. Lower down, the drive is taken from the center of the plain bearing, one-piece crank via a Hy-Vo chain to a jack shaft, that also provides a home to the generator assembly situated high up behind the cylinders. The power is then transferred to the 19-plate wet clutch through a pair of straight cut primary drives and then on to the six-speed box. It’s a design that is common in more modern times but back in 1981 this was cutting edge technology.
Yamaha kept much of the chassis department simple, despite the main competition coming from the Kawasaki GPz550, equipped as it was with air forks and more sophisticated rear damping. The running gear of the XJ mimics that of the LC series and, as such, was working hard to keep up with the extra weight. The basic engine concept did live on in the Yamaha range for a good while, the FJ, FZ and XJ600 models all owe a lot to the first of the Yam middleweights.
Dave Degens and Dresda
Dave Degens learned his trade working in his fathers engineering firm in the 1950s. He soon gained a passion for motorcycles, and started producing modified scooters for the London based Dresda Autos. When this business came up for sale in 1963, Dave took the step and bought into the retail side of the game, he kept the scooter side of the business going, but undertook the building of motorcycles too. Having already built three Tritons, the marriage of a Triumph engine and Norton featherbed frame, he quickly became known as a builder of fine café racers, his not inconsiderable racing successes, and riding talent too, backed this up.
Degens’ knowledge soon saw him modifying Japanese machinery, making wider swing arms and beefier frames for those who could see the deficiencies in the designs from the far east. During the 70s and 80s, Dresda offered a range of frame kits enabling the end user to create a bespoke machine, using as much or as little as the firm offered, a price list of the day shows the vast array of options.
This brings us to the story behind the XJ turbo “It all began as a standard Yamaha that had been crashed” Dave recalls “The owners name escapes me now, but I do remember the end result as the DVLA wanted to class it as a brand new machine and charge the full amount of tax and VAT on the project. In the end we battled with them and eventually they agreed to transfer the registration details from the damaged machine to the new Dresda modded version. The chassis is a complete one off, albeit based upon my Superbike chassis of the time but greatly scaled down to match the compact engine.
“I wasn’t in agreement with the idea of fitting a turbo, a normally aspirated engine is a far better bet, as I have shown over the years with my own race winning machinery. The completed project was damaged yet again a few years later in the great storms of 1987, the owner’s garage roof succumbed and the bike was left in the elements for some time. It was returned to Dresda to be restored to its former glory and I’ve heard nothing of it since, until now.”
Dresda Yamaha XJ550 Turbo Specifications
- Engine – Air cooled, four stroke, transverse four cylinder, DOHC, 4 valves per cylinder
- Capacity – 528.7cc
- Bore & stroke – 57 x 51.8 mm
- Compression Ratio – 9.5:1
- Carburetion – Turbo
- Max Power – 84bhp @ 10500rpm (50bhp @ 9000 rpm std XJ550)
- Torque – 46ft-lbs @ 9000rpm (34ft-lbs @ 7500rpm)
- Ignition – CDI
- Transmission – 6-Speed wet clutch chain final drive
- Frame – Dresda steel cradle
- Suspension – 35mm telescopic forks, twin Marzocchi dampers adjustable for preload
- Wheels – 300 x 19 110/90 x 18
- Brakes – 2 x 265mm discs single-piston floating-calipers, 180mm Single leading shoe drum
- Wheelbase – 1416mm
- Weight – 204kgs
- Fuel capacity – 16ltrs
- Top speed – 145mph (112mph std)
Yamaha Dresda XJ550 Turbo
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