3.20. Replacement of the piston


We take the piston with a rod from the block of cylinders (see Replacement of inserts of a bent shaft).

In the lower heads...

... and covers of rods steel-aluminum inserts are established.

From a provorachivaniye they are kept by the locks entering cuts of beds.

We clamp a rod in a vice and, unclenching, we remove top...

... and lower compression rings. At their subsequent installation the tag "TOP" or "TORAHS" has to be directed to the piston bottom.

Inscriptions on a ring can not be, but the lower compression ring is always established by a facet down.

We remove an oil scraper ring...

... with a dilator.

Having installed the piston on a wooden mandrel with an opening or holding on weight, we beat out a finger.

We collect conrod and piston group in the return sequence.

We select the new piston. The class of the piston is designated by a letter, and category of a finger – figure (see the table of the interfaced details).

The gap between the piston and the cylinder at new details makes 0,05–0,07 mm. At wear the most admissible gap – 0,15 mm.
The finger which is correctly picked up, oiled engine has to enter piston openings under effort of a thumb of a hand and not drop out of the piston in vertical position.

Having installed a ring in the cylinder, a set of probes we check a gap in its lock. It has to be 0,25–0,40 mm for all rings. If the gap raised needs to be replaced rings.

We check a gap between a ring and a flute of the piston also a set of probes. For the top compression ring it has to be 0,045–0,077, lower – 0,025–0,057, oil scraper – 0,020–0,052 mm. A maximum permissible gap at wear – 0,15 mm.

We establish in piston flutes of a ring, then we focus them as follows:

  • we focus the lock of the top compression ring at an angle 45 ° to an axis of a piston finger;
  • we deploy the lock of the lower compression ring concerning the lock of the top ring to the opposite side;
  • we put the lock of an oil scraper ring on 90 ° concerning locks of other rings. At the same time the joint of its dilator has to be from the opposite side of the lock of the ring.

We warm the top head of a rod to 240 °C, having clamped it in a vice.

The finger can be cooled previously in the freezer.

We put on the piston a rod and by means of a mandrel quickly we press a finger.

The figures on a rod and its cover specifying number of the cylinder have to be on the one hand and coincide.

The tag "П" on the piston has to be directed to a forward part of the block of cylinders.