Volkswagen Golf Service & Repair Manual: Checking pistons and cylinder bores

Checking piston

Using a micrometre, measure approx. 10 mm from the lower edge, perpendicular to the piston pin axis.

Maximum deviation from nominal dimension: 0.04 mm

Piston diameter mm

Specification

74.42 ¹⁾

1) Dimensions without coating

Piston manufacturer Federal Mogul (thickness of 0.018 mm per side)

Piston manufacturer Mahle (thickness of 0.015 mm per side)

Measuring piston ring gap

Push piston ring at right angles to cylinder wall from above down into cylinder bore to approx. 15 mm from bottom end of cylinder.
Push in using a piston without piston rings.

Piston ring	New mm	Wear limit mm
Compression ring	0.20 ^{+ 0.15}	1.0
Oil scraper ring (2 parts)	0.20 ^{+ 0.20}	3.0
Oil scraper ring (3 parts)	0.50 ^{+/- 0.25}	3.0

Measuring ring-to-groove clearance

Clean annular groove of piston before check.

Piston ring	New mm	Wear limit mm
1st compression ring (piston ring manufacturer Federal Mogul)	0.050 … 0.090	0.15
1st compression ring (piston ring manufacturer Mahle)	0.035 … 0.085	0.15
2nd compression ring	0.030 … 0.070	0.15
Oil scraper rings (3 parts)	Not measurable
Oil scraper rings (2 parts)	0.04 … 0.08

Measuring cylinder bore

Risk of damage to the surface of the cylinder bore caused by incorrect machining.Do not machine cylinder bore (reboring, honing, grinding) with workshop equipment.

Using cylinder gauge -VAS 6078- take measurements at 3 positions diagonally in lateral direction -A- and longitudinal direction -B-.

Maximum deviation from nominal dimension: 0.08 mm

Cylinder bore diameter mm
Specification	74.5 + 0.015 ¹⁾ +0.005

Note Cylinder bores must not be measured when cylinder block is mounted on engine and gearbox support -VAS 6095-, as measurements may be incorrect.

Checking pistons and cylinder bores