Checking For Wear

→ Avoid contact with caustic fluid.

→ Wear personal protective gear.

→ Ensure that there is good ventilation.

→ If you do come into contact, wash off immediately with plenty of warm water and contact a doctor if necessary.

Information 

• When cleaning pistons, be careful of the hard layer on the first ring groove. 
• Be careful of the twist lock for the second ring groove. 

1. Clean removed pistons with solvent naphtha or acetone first. To determine the dimensional group (engraved on the piston crown), carbon deposits must be removed carefully.
   1. 1.1. To do this, we recommend that you clean the piston crown in an ultrasound bath or using a brass brush.

      Information 

      • If the wear limit is exceeded, the piston must be replaced. 
2. Check the piston diameter -D-  at the prescribed measuring point on the piston shank using an outside micrometer.

   Measuring point from lower edge of shank dimension X = 15 mm  .

   Fig 1: Checking Piston Shank Diameter

   Courtesy of PORSCHE CARS NORTH AMERICA, INC.

   The maximum wear allowed at the specified measuring point is 100 μm (= 0.1 mm). If this measurement is exceeded, the piston must be replaced. The reference measurements are listed in the table below. 

   PISTON DIMENSIONAL DESCRIPTION
   
   

   Dimensional group (in mm)	Engine MA.120	Engine MA.121	Wear in mm
   I	88.964 - 88.976	96.964 - 96.976	max. 0.1
   X	88.974 - 88.986	96.974 - 96.986	max. 0.1
   II	88.984 - 88.996	96.984 - 96.996	max. 0.1

   Piston rings and piston ring groove: 

   Piston rings:

3. Check piston rings for signs of wear.
   1. 3.1. Piston-ring end clearance is measured in the cylinder.

   Designation	Ring end clearance in mm	Explanation
   1st piston ring	< 0.4 mm	Measurement in cylinder
   2nd piston ring	< 1.0 mm	Measurement in cylinder, check gap ends (twist lock)
   3rd piston ring	< 0.8 mm	Measurement in cylinder

   PISTON RINGS SPECIFICATION
   
   

   Designation	Dimension in mm
   Ring groove 1	1.2 + 0.15
   Ring groove 2	1.5 + 0.15
   Ring groove 3	2.0 + 0.15

   Piston pin: 

   • Check for signs of wear and tear.
   • Dimensional check using outside micrometer:  diameter = 22.0 - 0.02 mm.