Engines: Engine Rebuilding: Engine final assembly
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Topic IntroductionHelp

Fit piston rings

Summary
Clean the cylinders and wipe a thin even film over the cylinder before installing the piston rings. The objective of this procedure is to show you how to fit piston rings.

Part 1. Preparation and safety

Objective

Fit piston rings

Personal safety

Whenever you perform a task in the workshop you must use personal protective clothing and equipment that is appropriate for the task and which conforms to your local safety regulations and policies. Among other items, this may include:

If you are not certain what is appropriate or required, ask your supervisor.

Safety check

Points to note


Part 2: Step-by-step instruction

  1. Clean the cylinders
    Rotate the block until the one of the decks is facing up and is level. Lock the stand in this position. Wipe the cylinders clean with a dry paper towel. Don't use a shop rag. Then put some clean engine oil on another paper towel and wipe a thin, even film all over the cylinders. Paper towels do leave some paper lint behind but that is much less damaging than the stray fibers that can come off a cloth shop towel.
    Rotate the crankshaft so that the forward rod journal is pointing down and is centered in the cylinder bore.
  2. Install expander ring and scraper rails
    Check that your piston rings are in order and hold the rod and piston assembly in a vice. The ring kit should have a label that says what each ring in the package is.
    First ring to go on is the oil expander ring, which slips into the bottom groove. Make sure the ends of the expander ring don't overlap.
    Now install the first of the oil scraper rails, which go above and below the oil expander ring. Start it about 45 degrees to one side of the expander gap, and slide it in between the roof of the groove and the top of the expander ring. When the edge of the ring is in, slowly work it clockwise around the piston. When you get to the other side of the piston slow down. The edge of the ring could scratch the side of the piston, so grasp it firmly and carefully pull it away from the piston, then drop the end of it in place above the expander ring.
    Start the other scraper rail about 45 degrees to the other side of the expander gap and slide it into the bottom slot. Work this ring around in the opposite direction, guiding it past the top scraper and into the bottom groove as you go. Pull it away slightly at the end, and drop into its groove.
    Double check that the expander ring gap is not overlapped. If it is, use two paper clips or picks to pull them apart until they click into alignment with the rails. It's important to rotate the rings now and make sure that nothing is stuck or crooked.
  3. Install piston rings
    The packaging or instruction sheet should tell you which compression rings are which. Find the ring for the lower groove first.
    Look closely at the ring, there's usually a label on one side of the ring, like a dot or a 'T' or some other marking. The marked side of the ring needs to face up. When you know which way the ring goes, hold the ring expander with one hand and steady the ring with the other. Only expand it just enough to get the ring to slip down past the first groove and into it's place in the second. It should rotate freely.
    A lot of top rings have a shiny look on the edges when compared to the second groove rings. Use the same technique, expand just enough with the top mark facing up and lower the ring into its place.
    Repeat the process for the rest of the pistons in the tray. If you have custom fitted rings, be careful you don't mix up the order. Each ring has to go into the bore that it was filed to fit.