Centralizing Le Crankshaft

[4thcoast]

Hi all. This is Stephanie here with some "bits" on crankshaft centralizing. I have been told that people who build 4-cylinders tend to become obsessed with setting spiral bevel gear backlash, (the backlash that exists between the two pinion gears in the overhead shot below) but before any of this or that can be done, the crankshaft must first be centralized. Consequences of a non-centralized crankshaft include: (1) Too much side load on the connecting rod and piston, causing excessive wear. This is illustrated in the exploded view of the connecting rod, wrist pin, and piston. In the first exploded photo, the 3 components are apparently aligned. This doesn't happen amongst all four connecting rods, as a lot of the time the staggered spacing of an individual connecting rod's throw won't be forged in an ideal placement. Individual rod "throw" may be .050" either way, and we must pick a happy medium as to how thick to machine the thrust flange on the #4 bearing. (2) Misalignment of crankshaft timing gear to camshaft timing gear. The original thrust flange on a Henderson (stock) # 4 main bearing was .375” (3/8”) , whereas the new bearings by 4th Coast are .420”, (.025” wider). This is done to compensate for the crankshaft thrust flange surface being ground, (which is done to alleviate the potential for grooving). Below are three photographs of the thrust flange. In two of them, you can see the raised surface; very subtle. The third picture of the thrust flange illustrates the flush surface that the new, wider bearing flange compensates for.

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[quote='4thcoast' pid='2375' dateline='1337196269']

[4thcoast]

[quote='4thcoast' pid='2375' dateline='1337196269']