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Do-It-Yourself Projects
Engine Assembly, Part 3: Fitting Rods and Pistons
By Wayne Scraba/
Printable version
Degree of DifficultyModerate
Estimated Time300 minutes
300 minutes
If the connecting rod is equipped with studs, cover them with protectors (most auto parts stores sell inexpensive jobs) or use a length of rubber tubing over the studs. The idea here is to prevent the rod studs from damaging the crank during installation. We also coat the connecting rod bearing with assembly lube.
At this point, you should be able to push the piston and rod assembly into the bore, simultaneously guiding the rod so that it falls in place over the crankshaft rod journal. In most cases, you can hand push the piston in. In others, a very light tap with the handle end of a clean plastic hammer handle works. The need for excessive force means the oil ring isn’t installed correctly.
Rotate the engine on the engine stand. Coat the rod bearing (cap end) with assembly lube and install. You can torque to specs at this point, using three steps to sneak up on the final assembled toque. Slide the rod from side to side. It should move easily. Repeat the process for all of the pistons and connecting rods. Double-check the final torque figures (we usually make it a practice to check them three times).
Wrap the engine in the plastic storage bag. You’ve completed this segment of the build.
Tools Used

  • Piston Ring Filing Tool
  • Piston Ring Squaring Tool
  • Tapered Piston Ring Compressor
  • Crankshaft Socket-1/2-inch Drive
  • 1/2-inch Drive Ratchet
  • 1/2-inch Drive Torque Wrench
  • Deadblow Hammer
  • Feeler Gauge Set
Photo Guide
Filing piston rings to fit isn’t new. It’s been a performance item for at least three decades. It’s not a tough job either, but you have to take your time. We use this ring filer from Sealed Power to get the job done. There are much more exotic machines out there, but this one accomplishes the job for little cost. The downside (in comparison to some of the three-digit cost jobs) is that you must grind small amounts, check, regrind and so on until the correct gap is reached.
Ring Filer for Filing Piston Rings
In the article we mentioned the use of a ring-squaring tool. Here’s the B&B Performance model in action. To recap, the piston ring is installed in a given bore. Next, the ring-squaring tool is placed over the bore (and into it – the tool has a machined step on the ID). You simply pull up on the ring, squaring it against the tool.
Piston Ring-squaring Tool
Once the ring is square in the bore, you can check the gap. Here, a common (but high quality) feeler gauge is used to check the gap.
Feeler Gauge Used to Check the Gap
Once the gap is set, it’s a good idea to very lightly de-burr the ring with a small, fine-tooth file. What you want to do is to gently remove the sharp ends the filing process creates.
De-burr the Piston with a Small, Fine-Tooth File
With the rings filed, it’s time to assemble the piston-wristpin-connecting rod package. Key components shown here are the pins, Spiral Loc retainers and, of course, the piston.
Assemble the Piston-Wristpin-Connecting Rod Package
Here’s a closer look at the Spiral Loc pin retainer along with the lock ring groove machined into the CP piston. The idea is to wind the lock into the groove.
Spiral Loc Pin Retainer
In this photo, you can see the rod, piston, pin and a special tool that’s designed to ease the pain of Spiral Loc or round wire retainer installation.
Rod, Piston, Pin and Special Tool Designed to Help with Round Wire Retainer Installation
During assembly, you have to ensure the piston and connecting rod is properly oriented. This means the rod big end side (and bearing) with the large chamfer must face the crankshaft fillet radius. The piston notch(s) must also be oriented correctly.
Ensure the Piston and Connecting Rod is Properly Oriented
As you can see, marking the piston surface with the bore number and the direction of installation (arrow faces forward) makes for easier assembly.
Mark the Piston Surface with the Bore Number and the Direction of Installation
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