TAKU125 Prototype 1 - Design Sheet
Date: 7/22/2026
Author: Arlo S. Young
For further information, please refer to my web page: www.mototalk.com
Cooling System Notes
The cooling system is a main point of discussion.
Using a mechanical belt link to power the pump will automatically increase pump speed with engine RPM. However, when the clutch is pulled in or the engine is left to idle, the bike will not circulate coolant.
A rubber belt driving the pump would be the ideal choice. However, the added space needed to install this system may result in packaging and weight issues.
Bill of Materials
Note: Prices displayed are above standard commercial value to account for other influences on price.
| Item | Estimated Price | Notes |
|---|---|---|
| TIG & MIG Welder — PrimeWeld MTS200 | ~$800 | Alternative: Everlast Lightning MTS 275 |
| AC/DC Everlast Lightning MTS 275 | ~$2,350 | Alternative welding machine |
| Motorcycle Frame Jig | ~$400 | Prevents chassis warping during welding |
| Drill Press | ~$520 | Any trusted brand |
| Metal Lathe — Precision Matthews PM-1030V | ~$2,899 | |
| Angle Grinder | ~$300 | Any trusted brand |
| Bench Vise | ~$60 | |
| Vortex Rok Shifter 125cc Engine | — | Primary engine |
| 55-Tooth Rear Sprocket | ~$35 | Lightweight aluminum preferred |
| #428 Non-Sealed Motorcycle Chain | ~$120 | Any trusted brand |
Total Estimated Cost
$8,100–$10,100
Estimated Specifications (Before Production)
Engine & Drivetrain
| Specification | Value |
|---|---|
| Dry Vehicle Weight | 175–195 lbs (79–88 kg) |
| Wet Vehicle Weight | 205–225 lbs (93–102 kg) |
| Target Power-to-Weight Ratio | 0.20–0.24 HP/lb |
| Engine | Vortex Rok Shifter 125cc single-cylinder two-stroke |
| Cooling System | Liquid-cooled via belt-driven external water pump |
| Maximum Power | ~43 HP @ ~13,900 RPM |
| Maximum RPM | ~14,000–14,500 RPM |
| Induction | Reed valve with Dell'Orto VHSH 30mm carburetor |
| Transmission | 6-speed sequential gearbox |
| Clutch | Manual multi-plate dry clutch |
Notes
- The dry weight target is intended to prevent excessive clutch slipping when launching from a stop.
- Wet weight includes premix fuel, transmission oil, and radiator coolant.
- RPM limit is based on engine specification sheets and is a loose estimate.
- The carburetor and gearbox are supplied standard with the Rok Shifter engine.
- Although the gearbox was designed for kart use, it is suitable for this motorcycle application.
Final Drive & Gearing
| Specification | Value |
|---|---|
| Chain Size | #428 high-tensile chain |
| Front Sprocket | 17-Tooth (stock Rok Shifter) |
| Rear Sprocket | 55-Tooth |
| Drive Ratio | 3.235 : 1 |
| Estimated Top Speed | ~82 MPH (132 km/h) @ 13,500 RPM |
| Chain Length | 126–132 links (TBD) |
Notes
- Use a non-sealed or slim O-ring chain for engine case clearance.
- Lightweight aluminum rear sprocket recommended to reduce rotating mass.
- Final chain length will depend on swingarm dimensions.
Chassis & Wheels
| Specification | Value |
|---|---|
| Frame | Full-size lightweight street-style frame |
| Front Wheel | 19-inch spoked rim |
| Rear Wheel | 17-inch spoked rim |
| Tire Size | 110/70-17 or 120/70-17 |
Notes
- Final frame design is to be determined in future drawings.
- Keep rotating mass as low as practical.
Fuel & Starting
- Standard two-stroke premix fuel
- Fuel ratio: 25:1–30:1
- Simple push-start system