Piston And Cylinder Bore, Checking

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Pistons, Checking

Fig 1: Checking Piston Bore

Courtesy of AUDI

-- 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

Cylinder Bore, Measuring

Fig 2: Checking Cylinder Bore (Dimensions)

Courtesy of AUDI

-- 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

-- 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

-- 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