Pistons And Cylinder Bore, Checking

WARNING: This page is about a different car, the 2015 Audi A7 Quattro, 2014 Audi A7 Quattro, 2013 Audi A7, and 2012 Audi A7. However, it is still accessible from the selected car via links, so may be relevant.

Fig 1: Checking Pistons

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.

Piston diameter mm
Nominal dimension	84.49 ¹⁾
¹⁾ Measurements with coating (thickness = 0.02 mm). The coating wears off.

Fig 2: Checking Cylinder Bores

Courtesy of AUDI OF AMERICA, LLC

-- Using the Cylinder Dial Bore Gauge VAS6078 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	84.51 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 0.30	0.80
2. Compression ring	0.50 to 0.70	0.80
Oil scraping ring	0.25 to 0.50	- ¹⁾
¹⁾ Not determined yet.

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	0.04 to 0.08	0.20
2. Compression ring	0.03 to 0.07	0.20
Oil scraping ring	0.02 to 0.06	0.15