On the XV1000-RR Mjølnir

Many times the start of a project is defined by the availability of a donor bike or parts of a bike. Sometimes a project starts with an idea. In this case, the emotional connection between Mike and the TR1 engine was the spark that lit things up. One day Mike suggested to use a TR1 engine for the next project and he memorized the loving relation he had with these engines. The rest of us, unaware of the special properties of this particular combustion engine, didn't quite understand Mike's enthusiasm but nonetheless didn't try to stop him either. One other day, Mike called me if I was around to open the door of the workshop. Ok, you guessed it: he walked in with a 981 cc air cooled v twin, once the power plant of someone's Yamaha XV1000 TR1. In fact, this engine had once belonged to Mike. He had sold it to a guy who wanted to build a special around it. Pity for this guy, lucky for us, that guy didn't finish and Mike had a chance to buy the engine back. Even the exhaust headers made by Mike years ago were still on it. They show the invested elbow grease in their blunt stainless-steel shine.

There it sat on the workbench. For a while. Well, for quite some time. It stared at me, tempted me, seduced me, and finally, lured me into taking on this endeavour. This is one beefy engine. In fact, it is somewhat like a Vincent in the sense that this one too works as a stressed member and contributes in holding the bike together as well as delivering the mechanical oompf. Now, what to do with it? The first thing that popped into my mind was to make it a really well handling sports bike. That's a challenge because the tr1 is not known for these properties. I sourced some parts from a 97 GSXR and mocked it up for further thought. Would be an easy build, with the frame reaching from the steering head to both cylinder heads only. Then Yuri came and said: it has to have STL suspension. At that point we just managed to get the Suzuki STL bike (see story below) to handle the way it should handle and that really boosted my confidence in STL. So, yes: the STL system deserves a purpose built bike to proof its value and that bike will be this one. Since then a fine GSXR telescopic fork is sitting in my office without purpose and the project took off with STL on top of the list of objectives. All puppies have a name, and we named this puppy XV000-RR Mjølnir, xv1000 for the engine, RR for being a racer and Mjølnir, the mighty hammer of Thor, god of thunder as just a cool moniker that Mike came up with.

I had to take the lessons learned from the Suzuki project seriously and improve the design of STL and make it fit to this engine. Hours of drafting, calculating, trial and error finally added up to a geometry that satisfied my wishes. Now the real challenge appears: the engine is the way it is and is not designed to be part of an STL system. It is heavy, asymmetrical, big and does not have a rear swing arm support. Let's start from there and make the GSXR swing arm fit. Good thing is that the original swing arm was mounted in the frame and the frame attached to the engine on some strong points. By cutting his XV1000 frames in half and taking the standing section out all together, the German XV1000 specialist Sepp Koch proved that those points are enough to take up the forces . He races those bikes, and they don't break. If it works for him, it should work for me too, so let's get to work and build a jig:

What do we have now? 1 engine, 2 wheels and a swing arm. How to put them together? Well, we don't know yet. There is a theoretical model of the front suspension, with some optimal dimensions and the experience of proto1. We need to position the engine first and then build the bike around it. Yuri suggested tot tilt the engine forward a bit and that was indeed a good idea. It provides just a little extra space and it lowers the COG. Oh, and it looks cool too. We've figured out the lateral mass centreline and it proved to be right on the split of the engine casing. The builder's laser level turned out to be really helpful in setting up the jig although it remained a tedious job with many fall backs and desperate moments.

Just before we threw the whole bike out the window of frustration, a new tool enriched our hacker-sphere: a 3d printer. Wow, that is a nifty piece of kit. Now we can accurately print the parts we designed before we build them for real. Wonderful. First parts to be developed like this are the brackets for the rear swing arm pivot. They are difficult. The engine is not symmetrical, so the two brackets turn out to be completely different. Measure, draw, print, fit, repeat. It took around 5 iterations per piece to find the right shape. Then I use FEA to calculate strength and stiffness and altered the design accordingly. One last print to fit and that's how it will be. Plastic is good enough for now, so that we can build on.

The project leaped forward with this new aide and soon we added footrests and the rear end was sorted. In the front there was a brief romance with a BMW front swinger. This was too good to be true, it embraced the front cylinder as if it were made for it and up-side-down it would really be able to do the job here. One thing was disturbing, the front cylinder is not in the mass centre of the engine and the swing arm had very little clearance from it. It lead to a eureka moment: If we want the front cylinder to be on the centre line of the bike, then the whole engine is shifted 14mm to the left. Miraculously that would solve the offset problem in the final drive chain. Obviously the original TR1 was not designed for a 180mm wide rear tyre, yet, the GSXR swinger was. So this is an easy choice: the engine will be offset and the front sprocket sits in its original position. Two problems solved, one new problem introduced: the whole bike is off balance now. To compensate for the offset mass of the engine (80 kg, 14mm) I placed the Ohlins shock for the front suspension on the right hand side next to the rear cylinder. (8 kg, 140mm) In the end, I couldn't get a short enough wheelbase with the BMW swinger so a custom front swinger was designed and constructed.  The newly built front swinger was made so that  the desired geometry could be achieved taking the possible position of the pivot in the frame into account. This pivot is down in the valley between the two cylinders, where a strong mount point can be found on the crankcase. Now its time to construct the frame. The frame connects the headstock to the front cylinder head, the front swinger pivot and leans on the rear head as well. Because of thermal expansion I made a sliding connection on the rear head, leaving one degree of freedom unconstrained.

Water jetting came into our world and made it better. I designed most parts with this production technique in mind. The way it works is simple, a highly pressurized jet of water with abrasive powder cuts through your material and a CNC router makes it cut the pattern you have drawn out for it. Advantage of this over laser cutting is that it brings almost no heat to the material. So I ended up ordering a strip of 20x200mm 6082T6 aluminium and sent it out to a cutter accompanied with a cutting pattern. The parts I got in return needed only a little machining and were exactly as expected. This combination of 3d printing, and water jetting of high strength alloy fits the needs of a one off project like this nicely.

Having all the structural parts in the house means that we can build up the bike and let it roll some wheels for the first time. This is a bit of a moment as you can imagine. It's like watching your baby´s first steps. Before this moment are many, many moments of total despair, falling down and getting up again. The trick of course is to keep getting up. So did we and that's how we got to celebrate this first milestone of the project, a rolling cycle that steers, brakes and is fully suspended.

What a joy! The sensation of achievement is overwhelming. Worth a drink to celebrate. Now, back to reality. The bike is rolling but isn´t finished at all. Let´s wire it up and start the engine! No. We already did that and it wouldn´t bring us anything worthwhile. Rather pick up the sheet of Aluminium that is waiting and transform it into a monocoque tank-seat unit! Now that was easier said than done. The shape I chose is easy, welding Aluminium is not. More than a long time and a lot of cursing later, the thing is finished. With some compressed air in it we search for the leaks and repair them. Welding Aluminium is getting better and better but still the leaks are everywhere. Eventually we decided to start over from zero. This time the sheets of aluminium came laser cut into shape and we could start clean and perfect. This time, Mike did the welding and that payed off. Nice, strong welds and no more leaks.  The monocoque bears the weight of the driver and holds the gasoline, the battery, ignition unit and the data logger. The rear end is covered by the attractive shape of the Carbon Fibre seat unit we made for yuri´s bike. Suddenly the mjølnir looks like a motorbike!  The team gets excited and we work on the electric system next. I made a new wiring diagram and we wired everything up accordingly. Not mentioning one faulty contact breaker, everything worked straight away. The list of essential things still to be done aproaches emptyness, and we get more and more excited! Of course it is freezing cold December weather when we fire her up for the first test ride. Not the best of riding conditions, nevertheless a very heart warming experience: