in brief overview , referring to fig1 , an exemplary embodiment of a variable valve timing system 1 is shown . the variable valve timing system 1 involves a cam shaft 4 which is tubular in cross - section . the cam shaft 4 includes typical cam shaft bearings 3 that provide longitudinal support and cams 9 to actuate poppet valves . inside the cam shaft 4 are three shafts ( 5 , 10 , and 18 ), two of which are tubular in cross - section ( 5 and 18 ). a pulley 2 ( or other suitable means , e . g ., sprocket ), is fastened to the front end of first shaft 18 , and is connected to the engine crankshaft &# 39 ; s pulley ( or other suitable means , e . g ., sprocket ) via a gilmer - type belt or chain , depending upon the particular application or design of the engine . therefore , first shaft 18 rotates as the engine &# 39 ; s crankshaft rotates ( typically , at ½ the crankshaft &# 39 ; s speed ). first shaft 18 contains a shoulder which becomes a bearing to prevent it from moving laterally inside the exterior surface 17 of the engine &# 39 ; s head . this shoulder is captured externally by a circular fitting 16 , which prevents the first shaft 18 from moving laterally out from the cam shaft 4 . inside this tubular first shaft 18 is located a tubular second shaft 5 . second shaft 5 contains longitudinal grooves 6 which accept short pins 7 pressed into first shaft 18 . this arrangement fixes second shaft 5 rotationally to first shaft 18 , and allows second shaft 5 to move longitudinally with respect to first shaft 18 . the external diameter of second shaft 5 increases at a point to fit against ( with certain clearance ) the internal surface of the cam shaft 4 . also , the internal diameter of first shaft 18 , and the external diameter of second shaft 5 are both sized to provide sufficient clearance for longitudinal movement with respect to one another . milled into second shaft 5 are two slots 8 , one opposite the other on opposite sides of second shaft 5 . these slots 8 are configured at an angle relative to the centerline of second shaft 5 , and each slot 8 accepts one of two short pins 22 pressed through the cam shaft 4 . these pins 22 and their corresponding slots 8 fix the cam shaft 4 rotationally to the first 18 and second 5 shafts . as second shaft 5 is moved longitudinally , in either direction , its angled slots 8 cause the camshaft 4 , via the short pins 22 , to rotate relative to first 18 and second 5 shafts , therefore relative to the crankshaft &# 39 ; s angular position . in this manner , the timing of the opening and closing of the valves is changed relative to the crankshaft &# 39 ; s rotational position . the longitudinal movement of second shaft 5 is accomplished by the longitudinal movement of the third shaft 10 . the right - ward end of second shaft 5 includes a shoulder through which is bored a hole to accept third shaft 10 . this third shaft 10 contains two each bearings — one on each side of the shoulder of second shaft 5 — to provide for moving second shaft 5 in either lateral direction . third shaft 10 does not rotate with second shaft 5 and in fact , does not rotate at all . rather , third shaft 10 moves longitudinally in either direction while second shaft 5 rotates about third shaft 10 . at the opposite end of third shaft 10 from the bearings is a segment 13 of the third shaft 10 which is threaded . along this segment 13 , flats are milled on opposite surfaces . these flats are captured by bearing surfaces milled through the external wall 11 of the engine &# 39 ; s head , thus preventing third shaft 10 from rotating . this passage through the head &# 39 ; s outer wall 11 involves two parallel sides , closed at top and bottom by two semicircles . the parallel sides capture the flats milled onto third shaft 10 , while the semicircular surfaces allow passage of the threaded and rounded surfaces of third shaft 10 . cylinder 12 is a round cylinder that is threaded internally and that contains an external groove . this groove is captured by a flange 20 with seal 24 , both of which are fastened to the external wall 11 of the head . fastened to cylinder 12 is a first sprocket 19 ( or pulley ), which is driven in either direction by an electric motor 15 and a second sprocket 14 ( or pulley ). turning cylinder 12 in either direction moves third shaft 10 laterally in one direction or the other , thus moving second shaft 5 longitudinally , and causing the cam shaft 4 to rotate with respect to the crankshaft &# 39 ; s rotational position . note that first sprocket 19 ( or pulley ) can be actuated / rotated using other means . for example , a rack and pinion arrangement , with the rack being actuated by either an electric motor or hydraulic mechanism could be substituted in this design . the results would be the same — i . e ., third shaft 10 would be moved longitudinally in both directions . the actuation of the electric motor 15 , its direction of rotation to vary the valve timing , and the time duration of the motor &# 39 ; s excitement can be determined experimentally to most effectively provide for increased engine efficiency . these parameters can be easily programmed into a modern engine &# 39 ; s computer , which controls several other engine functions . from the foregoing , it can be appreciated that the variable valve timing system of the invention provides for a virtually infinite number , between minimum and maximum limits , of valve timing variations , including increased or decreased timing durations , depending upon engine speed variations and other parameter changes as programmed into the engine &# 39 ; s control computer . these timing variations are accomplished by turning the drive motor / mechanism in one direction or the other , by its duration of excitement , and can be performed within engine cycles , assuming the selected drive motor / mechanism is sufficiently responsive . these characteristics provide for a continuously optimum engine efficiency and output profile , as compared to current systems ( e . g ., step function systems ), and / or systems which cannot dynamically alter valve opening durations . thus , in comparison to conventional variable valve timing systems , those of the invention provide improved engine efficiency , output and reliability while simultaneously reducing manufacturing production costs . while the above specification contains many specifics , these should not be construed as limitations on the scope of the invention , but rather as examples of preferred embodiments thereof . many other variations are possible . for example , the actuation of the threaded shaft can be performed via several different means , including using a rack and pinion type arrangement . in this arrangement , a rack replaces the chain / gilmer belt , with the electric motor driving the rack toward / away from the threaded shaft . or , the same could be accomplished using a hydraulic system similar to a small power steering system arrangement . high - pressure engine oil from the engine &# 39 ; s oil pump , for example , can provide sufficient power to energize a hydraulic actuation system . further , a vacuum system , whose source can be the engine &# 39 ; s air intake manifold , can provide adequate power ( e . g ., via vacuum solenoids ) for the system &# 39 ; s actuation . accordingly , the scope of the invention should be determined not by the embodiments illustrated , but by the appended claims and their legal equivalents .