Checking Piston 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 

• Original pistons from the Porsche Spare Parts Catalogue are only available in the dimensional group X. 
• Observe the different weight groups. 

1. Clean removed pistons with solvent naphtha. To determine the dimensional group (engraved on the piston crown), carbon deposits must be removed carefully, e.g. with a brass brush or in an ultrasound bath.

   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.

   Select the measuring point specified in the table.

   Fig 1: Checking Piston Shank Diameter

   Courtesy of PORSCHE CARS NORTH AMERICA, INC.

   Engine type	Measuring point from lower edge of shank
   M96.25 + M97.20	X = 18 mm
   M96.26	X = 16 mm
   M97.21 + 22	X = 15 mm

   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. 

   Dimensional groups: 

   Dimensional group (in mm)	2.7 l engine M96.25 + M97.20	3.2 l engine M96.26	3.4 l engine M97.21 + 22	Wear in mm
   I	85.468 - 85.486	92.968 - 92.986	95.980 - 95.990	max. 0.1
   X	85.478 - 85.486	92.978 - 92.986	95.990 - 96.000	max. 0.1
   II	85.478 - 85.496	92.978 - 92.996	96.000 - 96.010	max. 0.1

   Weight groups: 

   Weight group	Piston, complete, 987 2.7 l - Ø 85.5 mm M96.25	Piston, complete, 987 2.7 l - Ø 85.5 mm M97.20	Piston, complete, 987 3.2 l - Ø 93 mm M96.26	Piston, complete, 987 3.4 l - Ø 96 mm M97.21 + 22
   -	460 - 466 g	462 - 468 g	535 - 541 g	524 - 530 g
   +	466 - 472 g	468 - 474 g	541 - 547 g	530 - 536 g