| COMPRESSION RATIO CALCULATOR | ||||||||||
|
||||||||||
| 85mm x 88mm, B34 Engine - Amount of Liquid | ||||||||||
| Engine Size | 62cc | 62cc | 62cc | 62cc | 62cc | 62cc | 70cc | 72cc | 73cc | |
| Std = 499cc | 9.0:1 | 8.9:1 | 8.8:1 | 8.6:1 | 8.5:1 | 8.3:1 | 8.1:1 | 7.9:1 | 7.8:1 | C/Ratio |
| +20 = 505cc | 9.1:1 | 9.0:1 | 8.9:1 | 8.7:1 | 8.6:1 | 8.4:1 | 8.2:1 | 8.0:1 | 7.9:1 | C/Ratio |
| +40 = 511cc | 9.2:1 | 9.1:1 | 8.9:1 | 8.8:1 | 8.7:1 | 8.5:1 | 8.3:1 | 8.1:1 | 8.0:1 | C/Ratio |
| +60 = 517cc | 9.3:1 | 9.2:1 | 9.0:1 | 8.9:1 | 8.8:1 | 8.6:1 | 8.4:1 | 8.2:1 | 8.1:1 | C/Ratio |
| 71mm x 88mm, B32 Engine - Amount of Liquid | ||||||||||
| Engine Size | 43cc | 44cc | 45cc | 46cc | 47cc | 48cc | 49cc | 50cc | 51cc | |
| Std = 499cc | 9.1:1 | 8.9:1 | 8.7:1 | 8.5:1 | 8.4:1 | 8.2:1 | 8.1:1 | 7.9:1 | 7.8:1 | C/Ratio |
| +20 = 505cc | 9.2:1 | 9.0:1 | 8.8:1 | 8.6:1 | 8.5:1 | 8.3:1 | 8.2:1 | 8.0:1 | 7.9:1 | C/Ratio |
| +40 = 511cc | 9.3:1 | 9.1:1 | 8.9:1 | 8.8:1 | 8.6:1 | 8.4:1 | 8.3:1 | 8.1:1 | 8.0:1 | C/Ratio |
| +60 = 517cc | 9.4:1 | 9.2:1 | 9.0:1 | 8.9:1 | 8.7:1 | 8.5:1 | 8.4:1 | 8.2:1 | 8.1:1 | C/Ratio |
Position engine on
floor or bench with spark plug hole vertical and uppermost and piston
at TDC on compression stroke. Pour oil from a measuring jug until the
oil level is half up the plug hole. You need to take note of the start
and finish levels of oil in the measuring jug so that you can work out
how much oil has been poured into the engine.
From the charts above, you can immediately see your compression ratio,
providing you know what bore you are on (i.e. Std, +20", +40",
or +60").
This chart is based on calculation and experimentation and is approximately
one decimal place of compression ratio.
ENGINE
SPECIFICATIONS
| Engine Capacity | 348cc & 499cc | Con-rod Centres | 6 15/32 in | |
| Cylinder Bore (nominal) | 71mm & 85mm | Con-rod small end | Dia. 0.7505 in | |
| Cylinder Bore (actual) | 2.794-2.793 3.345-3.34 | Rocker Spindle | Dia. 0.561 in | |
| Stroke | 88mm = 3.462 in | Cam Spindle | Dia 0.6235 in | |
| Rocker Spindle | Dia 0.561 in | Cam Bush size | 0.625 in | |
| Valve stem Dia | (inlet 0.309 in) | Gudgeon Pin | Dia 0.750 in | |
| Valve stem Dia | (exhaust 0.348 in) | |||
| Valve Spring | (outer free length) | 1.670 in | ||
| Valve Spring | (outer fitted length) | 1.312 in | ||
| Valve Spring | (inner free length) | 1.500 in | ||
| Valve Spring | (inner fitted length) | 1.218 in | ||
| Inlet Valve Timing | (with 0.018 valve clearance) | |||
| Cam 65-2442 | O.B.T.D.C 65º | C.A.B.D.C. 85º | Lift 0.442 in | |
| Cam 65-2446 | O.B.T.D.C 63º | C.A.B.D.C. 72º | Lift 0.404 in | |
| Cam 65-2448 | O.B.T.D.C 43º | C.A.B.D.C. 73º | Lift 0.380 in | |
| Cam 65-2420 | O.B.T.D.C 25º | C.A.B.D.C. 65 º | Lift 0.300 in | |
| Cam 65-2444 | O.B.T.D.C 60º | C.A.B.D.C. 85º | Lift 0.422 in | |
| Exhaust Valve Timing | (with 0.018 valve clearance) | |||
| Cam 65-2446 | O.B.T.D.C 80º | C.A.B.D.C. 80º | Lift 0.404 in | |
| Cam 65-2450 | O.B.T.D.C 70º | C.A.B.D.C. 45º | Lift 0.380 in | |
| Cam 65-2452 | O.B.T.D.C 64º | C.A.B.D.C. 34º | Lift 0.370 in | |
| Cam 65-2491 | O.B.T.D.C 95º | C.A.B.D.C. 50º | Lift 0.421 in | |
| Cam 65-1891 | O.B.T.D.C 85º | C.A.B.D.C. 60º | Lift 0.423 in | |
| Cam 65-2420 | O.B.T.D.C 65º | C.A.B.D.C. 25º | Lift 0.300 in | |
| Magneto Points Gap | 0.010 in - 0.012 in | Valve stem guide clearance | 0.001-0.003 | |
| Ignition Timing Fully Advanced | 39º = (15/32) | Valve clearances | 0.006 | |
| Spark Plug Gap | 0.018-0.020 | Flywheel balance factor | 58% | |
| Push Rod Standard Length | 9.0625 excluding spigot | Valve Seat Angle | 45º | |
| Flywheel run out maximum | 0.002 |