Kinsler_Handbook_#32 December 2017

Kinsler Fuel Injection, Inc, 1834 THUNDERBIRD TROY, MICHIGAN 48084 U.S.A. Phone (248) 362-1145 Fax (248) 362-1032 62 HOW TO SET UP LINKAGE FOUR BAR LINKAGE Four Bar Linkage is called “Four Bar”, because it consists of four bars. Looking at Fig 1 : One bar is “ArmA”, the second is “Arm B”, the third is the “Hex Link”. The fourth is whatever holds the two shafts in place; a manifold casting, a bracket, etc. All the bars may be different lengths. THROTTLE SHAFT TRAVEL Since most throttle plates have a 14 o seat angle, they only have to rotate 76 o to be 90 o to the throttle bore, which is wide open throttle. THE SAFEST LINKAGE The safest linkage is one in which the driven armmakes a 90 o angle to the hex link at half travel, so the total travel is split evenly to both sides of the 90 o point... 38 o to each side. This keeps well away from having the driven arm go to an over-center position... see “CAUTION” on “Uneven Four Bar Linkage”, Page #59. PARALLEL FOUR BAR LINKAGE Parallel four bar linkage is when the hex link is made the same center-to-center (c-c) distance as the two shafts, and the c-c of “Arm A” is equal to “Arm B”. As the arms rotate they will remain parallel to each other, and the Hex Link will remain parallel to the Base Line. The significance is that “Shaft A” will move the same number of degrees as “Shaft B” at every point, which is needed when linking the shafts on the left and right side of the manifold, see Fig 1. PART THROTTLE AIR FLOW When using Parallel Linkage, the throttle shafts both rotate in the same direction, so the lower edges of all the throttle plates slope to the right or to the left. At part throttle this will direct the air differently to the ports on the right side of the engine versus the left. Some racers claim this gives rough part throttle operation. At wide open throttle the throttle plates are all straight open, so it won’t affect full power. OVER-UNDER LINKAGE Very difficult to set up properly . Over-Under linkage counter-rotates the throttle shafts allowing the throttle plates to be installed with the lower edge of each throttle plate out toward the valve cover. This will direct the air the same to every port as the throttles are opened. While the geometry can be set satisfactory, it is never exact (see table in Fig 2), and if the arms are loosened, it is difficult to get them back as they were... their initial angles are critical. Every shaft c-c distance and arm length combination requires different initial arm angles. DRAWING LINKAGE Measure the c-c of the two shafts to be connected. Though one shaft may be higher than the other, for convenience draw the shafts as horizontal. Draw a dashed Base Line and put the shaft centers on it. Draw an arc with the c-c of Arm-A. Draw another with the c-c of Arm-B. Draw lines from the center of the shafts to represent the initial trial position of the arms. The distance between these two points on the arcs is the length of the Hex-Link. Set the compass at this distance. Mark off 10 o increments along arc-A. Set the point of the compass on each of these and make a mark on arc-B for each. Example: see the 40 o and 40.5 o marks in Fig 2. Measuring the angles of the marks on arc-B allows a table to be made of the relative movements. If the numbers are not satisfactory, try other arm settings and/or Hex Link length. See “Shaft Rotation Ratio” on Page #59. Throttle plates that rotate the same direction, use parallel linkage Throttle plates that are opposite rotation, often use over-under linkage © 2017 JACKSHAFT LINKAGE... BECOMING MUCH MORE POPU- LAR This is much more desireable than the over-under linkage, as it is much easier to set up and gives each shaft the exact same rotation. CENTER BELLCRANK LINKAGE This also gives even shaft rotation, but there is not often enough room to fit it in. See Page #64. DRIVEN 0 10.3 20.5 30.3 40.5 50.8 61.0 70.8 76.0 DRIVER 0 10 20 30 40 50 60 70 76 o o