Several bike and quad guys I have talked to have said any numbers posted for bikes or quads is at the rear wheel. I looked up the specs and the Jawa is a 4 valve engine. Cam timing is also listed.
www.codyracing.com
Description of JAWA Engine Type 884 and 888
Single cylinder, single OHC with a swept volume of 500 ccm. Air-cooled, four valve with a bore of 85 mm and a stroke of 87 mm, or a bore of 88 mm and stroke of 81.2 mm. Engine oil sumps, head and cylinders are made from aluminum alloy. The big-end and main bearings are of caged needle-roller type. The camshaft is seated inside the head on needle bearings and is chain driven. Valves are at a 35 angle with one tapered helical spring per valve. Valve seats are hot pressed into the head. The forged piston is made of light alloy with two piston rings. The engine has a circulation lubrication system. The oil tank is situated in the valve gear cover and right hand crank case. The engine holds .6 litre of oil. The oil can be checked at the oil level gauge. A 34 mm carburetor is used with electronic ignition.
Technical Data
Model 884 bore / stroke 85 mm / 87 mm
Model 888 bore / stroke 88 mm / 81.2mm
Swept volume 493 ccm
Maximum power / RPM 63-70 bhp / 8500-10500 RPM
Compression ratio 13-15:1
Carburetor Dellorto 34 mm
Ignition advance 30 -33
Ignition PVL Electronic
Spark plug Champion G55R / G57R
Valve / cam timing 10A 13A 17A 01 02 03
Ex. valve open / close 69 /31 69 /31 67 /30 62 /30 66 /33 62/30
In, valve open / close 37 /67 34 /67 39 /62 31 /68 39 /62 37/68
(measured at a valve lift of 1 mm)
Valve clearance Int / ex .004" / .006"
Fuel Methanol
Oil (.6 litre) Silkolene Castorene R-50