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. l  Maximum deviation from nominal dimension: 0.03 mm. There are different piston sizes specifically matched to the varying bore dimensions for the cylinder block.

Piston Ø mm
For nominal bore dimension I	84.490 1)
For nominal bore dimension II	84.590 1)
l  1) Dimensions including coating (thickness 0.01 mm). The coating will wear down 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 bore dimension I	84.510 ± 0.005
Nominal bore dimension II	84.610 ± 0.005

Measuring piston ring gap –  Insert ring at right angle to cylinder wall from above and push down into lower cylinder opening approx. 15 mm from bottom of cylinder. –  To do so, use a piston without rings.

Piston ring	new mm	Wear limit mm
1st compression ring	0.20 … 0.35	0.80
2nd compression ring	0.20 … 0.40	0.80
Oil scraper ring	0.20 … 0.40	0.80

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

Piston ring	new mm	Wear limit mm
1st compression ring	0.035 … 0.085	0.200
2nd compression ring	0.005 … 0.045	0.150
Oil scraper ring	0.010 … 0.050	0.200