The supercharged two-stroke double-row radial ten cylinder engine
The whole project have started 2,5 years ago.
The main goal was to create my own engine design, something that had never been used before in any vehicle.
And most importantly I wanted engine design, for such, there are no engineering templates. (for example for inline 4 you can find numerous "stencils of formulas" and you just put your numbers in formulas on page 1 then you put the result from page 1 into the formula on page 2 etc and 40 pages of calculation later you have your engine designed and you don't have to know anything about physics or material science.
So I chose a supercharged two-stroke radial engine design, which had never been used in mass production before. So I had to make my own formulas.
Then I set a goal to make this project on edge of mechanical complexity. (but without self-purpose nonsense gadgets)
"One step further in complexity and I would need magic not science to make this engine work."
So one of the goals was as many cylinders as possible
-> Radial design is the most space-effective
-> Two rows of cylinders reduce engine diameter
-> One crankshaft with master rods -> engine diameter and height reduced (but the blower is needed to maintain scavenging cycle)
-> Rows overlap slightly + onesided slave rod connection -> height replacement created space for blower assembly between crankcase and frame.
-> Using 5 tiny roots blowers is more space effective and allowed me to use high blower rpm (up to 40 000 rpm) so blowers can be small enough to fit in the engine and still are capable to charge the engine. (1,6 charge to cylinders displacement ratio)
-> Then I compared the dimensions of 8,10,12 cylinder designs and I choose a maximum number of cylinders that still fit in the frame without cutting Jawas' frame. So I went for 10 cylinders. Now clearance of the engine/frame is about 1mm, so it is really close fit.
Base motorcycle: Jawa 18 (*1953)
Displacement: 10 x 50cc = 500ccm
Power: now limited to 60hp/6500 rpm---Calculated capability 120hp/10000 rpm--- Road legal setup is 12hp (safety reasons)
Gearbox: 4speed semi-automatic
Max speed: 220 kmh (only calculated, I don't recommend to try) in Road legal setup 100kmh
Layout: Radial double-row two-stroke
Aspiration: Supercharged (5x roots blower)
Weight: 155 kg
Suspension/ brakes: Friction silencers and drum brakes all stock (CZ government requirement can´t mess with those if I want to stay road legal)
Some more info about construction:
- Engine case, crankshaft, roots blowers assembly, master conrods were made on CNC mill
- Cylinders, pistons, slave rods, transmission case, and clutch are used stock from vintage Jawa motorcycles
- Exhaust headers and the intake manifold is hand-made and consists of 17 hand-crafted parts. That goddamed "pipe octopus" took almost a month of the cut/weld/cut/weld process. During manufacturing those tubes I got permanent inflammation in the carpal tunnel area caused by angle grinder vibration.
- Paint job I did myself except the last layer of clear. Thick gold lines and signs are plated by pure gold.
- Pistons and combustion chambers are ceramic coated to prevent overheating
I blew the engine 5 times
- Not enough clearance on the blowers gear cover. Blower shafts touched cover and loosen shafts screw causing tear cover of engine and busting blowers bearings (oil sprayed all over workshop)
- The second blow was because aluminum blower rotors got loose on steel driveshafts hexes caused them to rattle and then rotors touch each other resulted in inevitable jam causing gears to friction weld to shafts (pry bar and hammer used during disassembly)
- The third blow was because I was too slow during assembly and silicone hardened before I set up and assembled blowers, causing clearance reduced almost to zero and resulting in friction-weld rotors to blowers casing after less than 1min. run
- Ignition stator broke and start rotating with ignition rotor, and busted all sensors and wiring
- I completely broke the bevel gear used to connect the engine to the clutch. One bearing on the horizontal shaft got loose it caused the bevel to move a little bit that busted teeth clearance, which caused extreme teeth eroding and then slip.
Few other "happy day" events
- In beginning I used 5 separate carbs for each blower, this assembly was impossible to tune, and I always had problems with fuel flow or fuel leak so I made an intake manifold for one carb. now it works perfectly.
- Firstly I used 10pcs of CDI ignition, but it caused extreme e-mag noise. So it caused a misfire, and digital devices could work in a 2meter radius around started bike so I put it out and now I´m using TCI (inductive) ignition. And it works much better (ignition electronics is the only modern technology used in this bike, I shy out of old-school hammer/distributor solution)
- Engine carburetors (old design) caught on fire twice, then I threw them away. (Being living torch is not my cup of tea)
- My workshop is not heated so last winter when I was working overnight two of my toes froze black (took 8moths to heal)
- While working on headers I busted my hands by grinder vibration to the degree that I developed chronic inflammation of carpal tunnel
I never gave up.
Failure is certain but not finite. Unless I don't give up.
I emerged my self to pursuit my dream with dedication.
I worked on projects even when I didn't feel right. Last few weeks I literally hated to be in the workshop and push this project forward.
Now the project is finished motorbike is running smoothly,
Now I would like to share my experience with other people.
I hope that my story will make some other guys' and gals' day better and entertain them for a few minutes by reading or watching videos about my adventure.
It would make all this work and suffering worthwhile if I could manage to inspire even one person to adopt responsibility for fulfilling one's dream and push against odds, never give up, don't change direction when things get tough. For me it's not about building the bike, it's about conquering our inside dragons of self-doubt, fear, and false excuse.... We are stronger than we think, and we have to push hard to find our strength.