Jim Smart
June 30, 2007

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The Mock-Up
A mock-up can save a lot of grief when it's time for assembly and fire up. Mocking-up an engine early on establishes dimensions, enabling you to correct irregularities before final assembly.

A mock-up involves temporarily assembling the engine-crankshaft, bearings, pistons, and connecting rods-to measure tolerances. It should also include installing the cam and heads to check piston-to-valve clearances. To be absolutely certain of every aspect of an engine build, you need to check everything, including:

  • Short-block preassembly one cylinder bore at a time to check deck and compression height. Do this without installing piston rings.
  • Rod and crank-to-block clearances.Minimum clearance allowed is 0.060-inch. Parts grow when they get hot.
  • Piston-to-crank counterweight clearances; a 0.060-inch minimum.
  • Crankshaft endplay-0.004 to 0.008-inch. Maximum limit is 0.012-inch.
  • Connecting-rod side clearances should be 0.010 to 0.020-inch. Maximum allowable is 0.023-inch. Check again during final assembly.
  • Piston-to-cylinder wall clearances.
  • Piston ring and groove dimensions, including ring-side clearances.
  • CC valve reliefs to check valve-relief volume.
  • Ring end-gap clearances.
  • Main- and rod-bearing clearances.
  • Thrust-bearing and width clearances.
  • Install the oil pump to determine pump-to-crankshaft counterweight clearances; no less than 0.060-inch.
  • Oil pump rotor-to-housing clearances. Check for smooth operation by hand once the pump cavity has been oiled.
  • Piston-to-valve clearances on all cylinderbores.
  • Valve stem-to-guide clearances and movement. Valves should glide smoothly through guides. Check stem and guide widths.
  • Spring compression and pressure.
  • When installing heads for mock-up, use a head gasket but don't torque.
  • Measure (cc) chambers to determine volume. Record the numbers.
  • Intake manifold for proper fit without a gasket.