How to Install Pistons on Connecting Rods

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An engine's connecting rods are the components that connect the crankshaft to the piston. As the crankshaft rotates (which corresponds to the engine's RPM), the connecting rod and piston is pushed up and down, creating compression, as the piston slides up and down in the block. During an engine rebuild, the connecting rods must be fastened to the piston before the rod is bolted to the crank.

Things You'll Need

  • Pistons and wrist pins
  • Connecting rods
  • C-clips for the wrist pins
  • C-clip pliers
  • Engine assembly lube
  • Clean the pistons and connecting rods thoroughly. If you're not using brand new pistons, have a machine shop clean the pistons to remove all carbonization. (This can also be done with steel wool, a wire brush and WD-40.)

  • Remove the wrist pin from the piston. The wrist pin is the part of the piston that the small end of the rod rotates on. Use specially designed wrist pin pliers to remove the C-clips that hold the wrist pin to the piston. There is a small groove in the wrist pin and a corresponding groove in the piston that the clip goes into. To remove the clip, squeeze it together with the pliers and pull the clip out of the hole where the wrist pin goes.

  • Slide the wrist pin out of the piston. Repeat this process for all the pistons. (If you are using new pistons, they are probably not assembled.) NOTE: Do not mix up the wrist pins and pistons. Keep each wrist pin with its respective piston.

  • Clean the wrist pin, the connecting rod and the piston. Place a generous amount of engine assembly lube on the wrist pin inside the small end of the rod and the holes in the piston that the wrist pin goes through.

  • Slide the wrist pin through one side of the piston. When the wrist pin is part of the way inserted, place the end of the rod in the piston so that it lines up with the hole that the wrist pin goes through.

  • Continue sliding the wrist pin through the rod then through the other side of the piston. Heat up connecting rods using a torch (if necessary) to allow the metal to expand before the wrist pin will fit through it.

  • Insert the C-clips that hold the wrist pin in place. Use the special pliers to squeeze the clips into the grooves in the wrist pin and piston. Be careful not to bind or bend the clips as you install them. Repeat for each piston. After the wrist pin is installed, check the freeplay of the rod to make sure that it is not stuck or binding.

Tips & Warnings

  • C-clip pliers are available at auto parts and tool stores.
  • The connecting rods must be installed facing the right direction in order for them to be properly bolted to the crankshaft.

References

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