Villiers Technical Information:
4 Stroke Engines
Mark 10
| Bore | 50mm |
| Stroke | 50mm |
| Capacity | 98cc |
| BHP Mk 10 | 1.0 hp @ 2000rpm |
| BHP Mk 10 HS | 1.6 hp @ 3400rpm |
| Tappet Clearance - Inlet and Exhaust | Minimun .006in |
| Maximum .012in | |
| Points Clearance | .012in / .016in |
Mark 12
| Bore | 55mm |
| Stroke | 50mm |
| Capacity | 120cc |
| BHP Mk 12 | 1.2 hp @ 2000rpm |
| BHP Mk 12 HS | 1.95 hp @ 3400rpm |
| Tappet Clearance - Inlet and Exhaust | Minimun .006in |
| Maximum .012in | |
| Points Clearance | .012in / .016in |
Mark 15
| Bore | 63mm |
| Stroke | 47mm |
| Capacity | 147cc |
| BHP Mk 15 | 2.3 hp @ 3000rpm |
| Tappet Clearance - Inlet | .003in |
- Exhaust |
.006in |
| Points Clearance | .012in / .015in |
Mark 20
| Bore | 63mm |
| Stroke | 66.7mm |
| Capacity | 206.5cc |
| BHP Mk 20 | 2.5 hp @ 2500rpm |
| BHP Mk 20 HS | 2.7 hp @ 3000rpm |
| Tappet Clearance - Inlet and Exhaust | Minimun .006in |
| Maximum .010in | |
| Points Clearance | .012in / .016in |
Mark 25
| Bore | 70mm |
| Stroke | 66.7mm |
| Capacity | 256.5cc |
| BHP Mk 25 | 3.0 hp @ 2500rpm |
| BHP Mk 25 HS | 3.4 hp @ 3000rpm |
| Tappet Clearance - Inlet and Exhaust | Minimun .006in |
| Maximum .010in | |
| Points Clearance | .012in / .016in |
Timing a Villiers Engine
The magneto is timed so that the contact breaker points commence to open when the piston is 3/16" before top dead centre. A rough check on the position may be made without removing the cylinder head, by observing the position of the keyway on the driving shaft when the points are just opening. The keyway should then be 27deg before top. Accurate timing can only be done with the piston visible