Audi Workshop Service and Repair Manuals

Checking pistons and cylinder bores

Checking piston –  Using a micrometer (75 ... 100 mm), measure approx. 15 mm from the lower edge, perpendicular to the piston pin axis. t  Difference between actual and nominal diameter: not more than 0.04 mm.

		Piston Ø
Basic dimension	mm	82.465 1)
l  1)Dimensions not including graphite coating (thickness 0.02 mm). The graphite coating will wear down in service.

Checking piston ring gap –  Insert piston ring at right angle to cylinder wall from above and push down into lower cylinder opening approx. 15 mm from bottom of cylinder. Use a piston without rings to push ring into bore.

Piston ring Dimensions in mm	New	Wear limit
Compression ring	0.20...0.40	0.80
Oil scraper ring	0.25...0.50	0.80

Checking ring-to-groove clearance –  Clean groove in piston before checking clearance.

Piston ring Dimensions in mm	New	Wear limit
1st compression ring	0.06 … 0.09	0.20
2nd compression ring	0.03 … 0.06	0.15
Oil scraper rings	Cannot be measured

Checking cylinder bore Special tools and workshop equipment required t  Cylinder gauge -VAS 6078-   Caution Machining (reboring, honing, grinding) cylinder bore with workshop equipment is not permitted. The surface of the cylinder bore is damaged by machining. –  Use a cylinder gauge -VAS 6078- to take measurements at 3 points in transverse direction -A- and in longitudinal direction -B-. t  Difference between actual and nominal diameter: not more than 0.08 mm.

		Cylinder bore Ø
Basic dimension	mm	82.51

Note Measuring the cylinder bores must not be done when the cylinder block is mounted to the engine and gearbox stand -VAS 6095-, as incorrect measurements may result.