Installing the Crankshaft

- The crank bearings were thoroughly cleaned and slipped into place. I made sure that each bearing was always used in the same bearing cap throughout testing. The crank oil holes from the main bearings to the rods were cleaned with a brass wire brush to make sure that no obstructions were present. The crank was installed for the last time with generous amounts of Permatex Molylube (white grease) on the bearing surfaces.

crank

Crank installed and main caps torqued to spec

The main bearing caps were installed in the correct location with the arrows pointing to the front of the engine. I purchased new aftermarket 12 point main bolts as they were cheaper than purchasing original Chev main bolts.

Looks like the newly machined crank is bent at the snout (where the harmonic balancer sits). I put in the new harmonic balancer ($100) and still have the vibration problem. Measured the crank snout and there's 0.010" out of round. It should be less than 0.001". Talked to another machine shop and they verified that there's pretty much nothing that I can do at this time. My machineshop has asked me to bring the crank in to verify and if it is out, they'll replace it free of charge.

The crank was bad, the machine shop dials in the crank using the area between the timing gear key and the harmonic balancer key. I measured it and it was deadnuts on but both the timing gear and harmonic balancer were out by 0.010". We looked at what we could do to salvage the crank and the only things that we could come up with were:

  • Welding up the snout and taking it back down on a lathe to size - the heat from welding would most likely warp the crank. Just needs 0.001"of warpage to screw up the crank.
  • Spray welding - this wouldn't work as there is key slots. The weld would peal. Spray welding is used for press fitted pieces. I had another machine shop verify this with two journeyman machinists.
  • Chrome plating - Best bet but it is expensive and the machineshop didn't have their chrome plating tank up and running.

They did have two extra 400 cranks in the back. The first one was junk so they loaded up the second and it was good. The result was that they supplied me with a new crankshaft turned to my dimensions and new rod bearings as they had to go 0.010" more on them to clean them up. So I have a new crankshaft that measures perfectly. It's in the engine and the engine finally after 4 months purrs better than I expected.

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Copyright May 2011 Eugene Blanchard