tecnical data Useful Data
COMPRESSION RATIO CALCULATOR, ( From Roy Shearwood's WebSite )

85mm x 88mm, DB34 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 = 348cc 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 = 353cc 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 = 358cc 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 = 363cc 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 bench with spark plug hole vertical and uppermost with the piston at TDC on compression stroke. Pour fluid from an accurate measuring jug until the fluid level is half way up the plug hole. Make a note of the amount of fluid oil used
From the charts above, you can work out your compression ratio, providing you know what bore you are on (i.e. Std, +20", +40", etc ).

CAPACITY CHECK (CC )
STROKE =88 BORE =71   71 -: 2 =35.5 x35.5=1260 .25 x 88 =10902 x 3.142 =348454.084-: 1000 = 348.45 cc

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 65   C.A.B.D.C. 85 Lift 0.442 in
Cam 65-2446 O.B.T.D.C 63   C.A.B.D.C. 72 Lift 0.404 in
Cam 65-2448 O.B.T.D.C 43   C.A.B.D.C. 73 Lift 0.380 in
Cam 65-2420 O.B.T.D.C 25   C.A.B.D.C. 65 Lift 0.300 in
Cam 65-2444 O.B.T.D.C 60   C.A.B.D.C. 85 Lift 0.422 in
       
Exhaust Valve Timing (with 0.018 valve clearance)      
       
Cam 65-2446 O.B.B.D.C 80   C.A.T.D.C. 80 Lift 0.404 in
Cam 65-2450 O.B.B.D.C 70   C.A.T.D.C. 45 Lift 0.380 in
Cam 65-2452 O.B.B.D.C 64   C.A.T.D.C. 34 Lift 0.370 in
Cam 65-2491 O.B.B.D.C 95   C.A.T.D.C. 50 Lift 0.421 in
Cam 65-1891 O.B.B.D.C 85   C.A.T.D.C. 60 Lift 0.423 in
Cam 65-2420 O.B.B.D.C 65   C.A.T.D.C. 25 Lift 0.300 in
         
Magneto Points Gap 0.010 in - 0.012 in   Valve stem guide clearance 0.001-0.003
Ignition Timing Fully Adv'd 39 = (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 45
Flywheel run out maximum 0.002