'CC Quickies
Did you know that you can advance the timing on a Chevy by grabbing the vacuum advance and pulling? This rotates the distributor counterclockwise.>>>
As to the question of bolts versus studs, let's stick with the cylinder-head application. When bolts are torqued, a twisting motion is created between the bolt head and the threads. With a stud and nut, the twisting motion is eliminated, assuming that the stud was properly installed into a blind hole. All studs should only be installed hand-tight; never torque a stud into a blind hole. By eliminating the twisting motion, the full torque applied to a stud is used to create motion in one direction-stretch. This increases the clamp load. There isn't a great deal of difference in actual torque values between studs and bolts, but the difference is definitely there. Also, using a stud exerts less wear on the block threads, which improves block life. This is especially important in aluminum- or older iron-blocks where the head-bolt threads may be exposed to corrosion from engine coolant. This is also why professional engine builders use ARP-style thread-chasing taps to clean head-bolt holes in the block. These special taps merely clean the threads without removing metal, and more material is left for thread engagement between the bolt/stud and the block. Insufficient thread engagement is a common cause of pulled threads.
Now let's deal with the question of rod bolts and their effect on rod big-end concentricity. First, we can't emphasize enough the idea of using a rod-bolt stretch gauge as opposed to a torque wrench for tightening connecting rod bolts. We lost an engine several years ago when a rod bolt loosened up after being properly installed with a certified torque wrench with the proper lube. The rod cap came off (and destroyed the engine) because the bolt was not preloaded with sufficient stretch. A rod bolt is designed to stretch a certain amount in order to maintain sufficient tension (load) to keep the rod cap on the rod. We just performed this test again using brand-new ARP rod bolts for an engine we are building. The published ARP spec using ARP's moly paste for a small-block Chevy rod bolt is 50 lb-ft of torque. We'll admit that we have not had this particular clicker-style torque wrench calibrated, although it is only one year old. The proper rod-bolt stretch figure for this ARP 190,000-psi bolt is 0.0063 inch. When we torqued four different ARP rod bolts to 50 lb-ft using ARP's thread paste, we averaged 0.005-inch stretch for all four fasteners. We had to raise the torque to 59 lb-ft in order to achieve an average of 0.0061 inch for these same bolts. We did not measure the effect of torque load on connecting-rod concentricity because it's really not an issue. It's possible that overtightening the fastener might squeeze the big end of the rod, but that also means you're in danger of failing the bolt because it's overtightened. This is why measuring connecting-rod bolt stretch is so important-these bolts are the most highly stressed fasteners in the engine.
If we haven't bored you to death with all this technical stuff about bolts, it really is important information you need in order to properly assemble engines and suspension components. That connection is only as good as the fastener you use to bolt it together.
Fuel-Pressure Dilemma
Chris Gower, via CarCraft.com: I have a very strange fuel-pressure problem. The motor is a 350 Chevy with a 284/296-duration, 0.507/0.510-inch-lift cam. It's topped off with a single-plane intake and Dart Iron Eagle heads. I am running a 650 AVS Edelbrock carb. I installed a fuel-pressure gauge this spring and discovered 2 to 3 pounds of pressure. I then replaced the fuel pump.