Pistons And Cylinder Bore, Checking

WARNING: This page is about a different car, the 2015 Audi S7, 2015 Audi RS 7, 2014 Audi S7, 2014 Audi RS 7, and 2013 Audi S7. However, it is still accessible from the selected car via links, so may be relevant.

Fig 1: Checking Pistons With External Micrometer

Courtesy of AUDI OF AMERICA, LLC

-- Measure approximately 15 mm from the lower edge at a 90° angle to the piston pin axis using a 75 to 100 mm external micrometer.

Maximum deviation from nominal dimension: 0.03 mm.

Matching pistons are allocated to the different manufacturing stages of the cylinder block.

Piston diameter mm

Engine codes

CEUC/CEUD

CRDB

Nominal dimension

84.470 ¹⁾⁽¹⁾

84.490 ¹⁾⁽¹⁾

Repair stage

84.580 ¹⁾⁽¹⁾

84.590 ¹⁾⁽¹⁾

⁽¹⁾ ¹⁾ Measurement with coating (thickness = 0.018 mm). The coating wears off.

Fig 2: Checking Cylinder Bores

Courtesy of AUDI OF AMERICA, LLC

-- Using the Cylinder Dial Bore Gauge VAS 6078 measure in a diagonal sequence at three positions transversely -A- and longitudinally -B-.

Maximum deviation from nominal dimension: 0.08 mm.

Cylinder bore diameter in mm

Nominal dimension

84.510 ± 0.005 ¹⁾⁽¹⁾

Repair stage

84.610 ± 0.005 ¹⁾⁽¹⁾

⁽¹⁾ ¹⁾ measure 50 mm inside the cylinder bore.

Fig 3: Checking Piston Ring Gap

Courtesy of AUDI OF AMERICA, LLC

-- Push the piston ring squarely from above down to approximately 15 mm from the bottom end of the cylinder.

-- Use a piston without a piston ring for sliding in.

Piston Ring	New mm	Wear limit mm
1. Compression ring	0.20 to 0.35	0.80
2. Compression ring	0.20 to 0.40	0.80
Oil scraping ring	0.20 to 0.40	0.80

Fig 4: Checking Piston Ring Groove Clearance

Courtesy of AUDI OF AMERICA, LLC

-- Clean the piston ring groove before checking.

Piston Ring	New mm	Wear limit mm
1. Compression ring	0.035 to 0.085	0.200
2. Compression ring	0.005 to 0.045	0.150
Oil scraping ring	0.020 to 0.055	0.200