Assembly of the connecting rod and piston group of the K4M engine

Assembling the K4M Engine Piston-Connecting Rod Assembly — Fitting the Piston Pins and Rings

The piston pins are fitted with interference in the upper connecting rod eyes and rotate freely in the piston bosses, so heat the upper connecting rod eye to a temperature of 250 °C.

During assembly it is convenient to use the Mot574-22 kit and the Mot574-24 tool.

Dismantling and checking of the K4M engine piston-connecting rod assembly was covered in the article — “Dismantling and inspection of the piston-connecting rod assembly”.

Visually check the condition of the connecting rods (twisting and bending) and the cleanliness of the mating surfaces of the cap and the connecting rod eye.

To heat the upper connecting rod eye, use a 1500 W electric hot plate. Place the upper connecting rod eyes on the hot plate. Make sure that the upper connecting rod eyes contact the hot plate over their entire surface.

Place a piece of tin solder on each connecting rod eye as a temperature indicator. The melting point of tin solder is approximately 250 °C. Heat the upper connecting rod eyes until the solder melts.

Preparing the piston pins

Check whether the piston pins rotate freely in the bosses of the corresponding new pistons.

For fitting, use the C13 and A13 drifts from the Mot574-22 kit for piston pins without a collar, or the C13 and A13 drifts from the Mot574-24 kit for piston pins with a collar.

Preparing the piston pins
Fig. 1. Preparing the piston pins: 1 — piston pin; 2 — fitting drift; 3 — centring drift
  1. Fit the piston pin (1) onto the fitting drift (2) (see Fig. 1).
  2. Screw in the drift (3) until the assembly is tightened.
  3. Unscrew the drift (2) by a quarter of a turn.

Position of the pistons relative to the connecting rods

The pistons are marked with a “V” mark on the crown, which must be located on the flywheel side.

Position of the pistons relative to the connecting rods
Fig. 2. Position of the pistons relative to the connecting rods
  • Position the piston crown with the “V” mark upwards (see 1, Fig. 2).
  • Direct the groove for the connecting rod shell retaining tab downwards (see 2, Fig. 2).

Assembling the piston with the connecting rod

Assembling the piston with the connecting rod
Fig. 3. Assembling the piston with the connecting rod: 1 — ring B10; 2 — clamp
  1. Fit ring B10 onto the prism (see 1, Fig. 3), the piston resting on the ring, and secure all parts with the clamp (2).
  2. Make sure that the piston pin hole coincides with the hole of ring B10.
  3. Lubricate the drift and the piston pin with engine oil.
  4. Leave the piston pin in the assembly and check whether it rotates freely. If necessary, centre the piston.

The following operations must be carried out quickly to prevent cooling of the connecting rod eye.

  1. When the piece of solder has melted, remove the solder.
  2. Insert the centring drift into the piston.
  3. Insert the correctly oriented connecting rod into the piston.
  4. Quickly press in the piston pin until the centring drift stops against the bottom of the tool.
  5. Make sure that the piston pin does not protrude from the piston in any position of the connecting rod.

Fitting the piston rings

The piston rings are matched to the piston and must move freely in the piston grooves. Observe the fitting direction of the rings (the “TOP” mark must face upwards).

Arrangement of the piston rings
Fig. 4. Arrangement of the piston rings: 1 — upper compression ring; 2 — lower compression ring; 3 — oil scraper ring expander; 4 — oil scraper ring discs

Observe the position of the gap of each ring (see Fig. 4). The gaps of the compression rings must be staggered by 180°, the gaps of the parts of the oil scraper ring — by 120°.