I think the 66cc had a 40mm stroke with an 89mm conrod, as where the 48cc has a 38mm stroke with a 85mm conrod. The piston diameters seem correct, but you might want to add these: http://www.spookytoothcycles.com/images/engines/engine-ID.jpg
They should all have a 38mm stroke/85mm conrod other than the 66cc.
That's an easy question to answer: cut a half inch wide strip from the top of a cereal box, approximately 3 inches long. With the magnet is in the horizontal position, slide the cardboard strip around the magnet and along the upper and lower arms of the magneto coil.
Now with the magneto coil screws loosened, turn the crankshaft so that the magnet is in the vertical postion. Tighten the screws and remove the cardboard strip.
Here are the measured distances from the top of the stock cylinder: engineexhausttransfersintake* piston skirt**
48cc 28mm 32mm 55.5mm 44.8mm
60cc 28.7mm 33.1mm 56.3mm 45mm
66cc 29.3mm 33.1mm 57mm 44.7mm
* measured to bottom of intake port
** measured from top edge of piston
(66cc is the cylinder the factory calls 80cc. It is 66cc when measured the most common way.)
Assuming a .7mm deck height (distance from top edge of piston to top of cylinder at TDC) here are the port durations in degrees: engineexhausttransfersintakeblowdown*
48cc 140.7 110.3 113 15.2
60cc 135.7 100.6 116.8 17.6
66cc 141.6 114.7 117.6 13.5
* blowdown is the number of degrees that the exhaust gas has to exit the exhaust port before the transfers open. For this engine 20 degrees is perfect if ported per my recommendations.
To have perfect 157/117/120 degree port durations and 20 degree blowdown change the distances to these: exhausttransfersintake or piston
25.6mm 31.2mm 56.8mm 44.5mm (48cc, 60cc)
26.9mm 32.8mm 57.1mm 44.6mm (66cc)[/FONT]
whaaa? like valve overlap, lift, open degrees, and all that jazz?
noone seems keen on doing that sort of mods to the huasheng, and as the predators are a "race" motor from briggs and stratton, with plenty of upgraded cams etc available, the info for them will be elsewhere.
such as here. there appears to be roughly 100 camshafts to choose from.