Piston And Cylinder Bore, Checking

WARNING: This page is about a different car, the 2024 Audi A8 Quattro, 2023 Audi A8 Quattro, and 2022 Audi A8 Quattro. However, it is still accessible from the selected car via links, so may be relevant.

Pistons, Checking

Fig 1: Checking Piston Bore

Courtesy of AUDI OF AMERICA, LLC

-- Measure approximately 10 mm from the lower edge at a 90° angle to the piston pin axis using a 75 to 100 mm outside micrometer.

Maximum variance from the specified size: 0.017 mm.

Piston diameter in mm
Specified size	85.98 ¹⁾
¹⁾ Measurement with coating (thickness = 0.04 mm). The coating wears off.

If the wear on the coating -arrow- on the piston shaft is so well advanced, as shown in the image, the pistons must be replaced.

Courtesy of AUDI OF AMERICA, LLC

Cylinder Bore, Measuring

Fig 2: Checking Cylinder Bore (Dimensions)

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 the specified dimension: 0.005 mm.

Cylinder bore diameter in mm
Specified size	86.01 ¹⁾
¹⁾ measure 50 mm inside the cylinder bore.

Piston Ring Gap, Measuring

Fig 3: Checking Piston Ring Gap

Courtesy of AUDI OF AMERICA, LLC

-- At a right angle to the cylinder wall, push the piston ring from above down into the lower cylinder opening until it is approximately 15 mm from the edge of the cylinder.

-- Use a piston without a piston ring for pushing it in.

Piston Ring	new mm	Wear limit mm
1. Compression ring	0.15 to 0.25	0.35
2. Compression ring	0.30 to 0.45	0.55
3-part oil scraping ring	cannot be measured

Piston Ring Height Clearance, Measuring

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	0.03 to 0.08	0.15
2. Compression ring	0.02 to 0.07	0.15
3-part oil scraping ring	cannot be measured