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Here is an interesting article about the Iuz-fe engine on this very topic. [ http://www.lextreme.com/Cam-Timing.html ] The guy has some pretty astounding revelations. like: As a part of every high performance rebuild any good engine builder is going to “true up” or resurface the heads and block of the engine, in order to ensure “his” build has the very best flat sealing surfaces possible. Let’s take another hypothetical example to see what happens when he does this. Let’s say the builder takes off 0.005” from each head, and from each side of the block. That’s 0.010” from each bank, or 0.020” total, right? Now does that mean the timing belt has become 0.020” too long? No, it has become TWICE that, or 0.040” too long. Why? Refer to the diagram below, and notice what happens if a cam timing pulley is moved inward toward the crank by 1mm. Is the length of the belt affected by only 1mm? No, the effect is double, because the belt passes on both sides of the pulley, and has 180 degrees of wrap, or more. Now that we’ve seen how taking off 0.020” worth of material has translated into a timing belt that is 0.040” too long, let’s translate this into timing error. We know that the upper pulleys have 48 teeth and the pitch of these teeth is 8mm. Therefore the “pitch” circumference of the pulley is 48 x 8 = 384mm. Now if we have an error of 0.040”, this is 1.02mm, or 1.02 x 360/384 = 0.96 degrees at the camshafts, or twice that at the crankshaft. Makes it s little easier to understand how just shaving the heads and block can change the timing.
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