Audi Workshop Service and Repair Manuals

Checking pistons and cylinder bores

Checking piston –  Using a micrometer (75 ... 100 mm), measure approx. 10 mm from the lower edge, perpendicular to the piston pin axis. l  Maximum deviation from nominal dimension: 0.05 mm. There are different piston sizes specifically matched to the different dimensions of the cylinder block.

Piston Ø mm
Nominal dimension	82.924 … 82.936 1)
Repair oversize	82.964 … 82.976 1)
l  1) Dimensions not including coating (thickness 0.02 mm). The coating will wear down partly in service.

Measuring cylinder bore –  Use a cylinder gauge -VAS 6078- to take measurements at 3 points in transverse direction -A- and in longitudinal direction -B-. l  Maximum deviation from nominal dimension: 0.08 mm.

Cylinder bore Ø mm
Nominal dimension	83.006 … 83.014 1)
Repair oversize	83.046 … 83.054 1)
l  1) Measure at 50 mm into cylinder bore.

Measuring piston ring gap –  Insert ring at right angle to cylinder wall from above and push down into lower cylinder opening approx. 50 mm from bottom of cylinder. –  To do so, use a piston without rings.

Piston ring	new mm	Wear limit mm
1st compression ring	0.25 … 0.40	0.60
2nd compression ring	0.70 … 0.90	1.20
Oil scraper ring	0.25 … 0.50	0.70

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

Piston ring	new mm	Wear limit mm
1st compression ring	0.009 … 0.130	0.160
2nd compression ring	0.05 … 0.09	0.11
Oil scraper ring	0.03… 0.07	0.10