Pistols and Cylinders

GENERAL 131-1

Special tools 131-1

PISTONS AND CYLINDERS 131-1

Piston weight, checking 131-2

Cylinder height, checking 131-2

Cylinder roundness, checking 131-3

Piston and cylinder wear, checking 130-3

Piston rings 130-4

TABLES

a. Piston and Cylinder Identification 131-1

b. Weight Classes for Mahle® Pistons 131-2

c. Weight Classes for KS® Pistons 131-2

d. Cylinder Height 131-2

e. Mahle® Piston and Cylinder Sizes 131-3

f. KS® Piston and Cylinder Sizes 131-4

g. Piston Ring End Gap Clearance 131-4

h. Piston Ring Side Clearance 131-4

Special Tools

Ring Expander

Special tool

A VW 121 b Piston ring expander

B 65 Piston ring groove cleaner

(source: Baum Tools Unlimited)

C 17 Inside bore gauge

(source: Baum Tools Unlimited)

(source: Baum Tools Unlimited)

Special tool

A VW 121 b Piston ring expander

B 65 Piston ring groove cleaner

(source: Baum Tools Unlimited)

C 17 Inside bore gauge

(source: Baum Tools Unlimited)

(source: Baum Tools Unlimited)

GENERAL

This repair group provides reconditioning information for the pistons and cylinders. Engine disassembly is described in 102 Engine Disassembly and Assembly.

The information contained here is intended to be used as a reconditioning guide for the professional or experienced automotive technician.

Special tools

^ Some of the procedures require special tools.

PISTONS AND CYLINDERS

Pistons must be matched by weight. When replacing pistons and cylinders, always check with an authorized dealer for the latest in replacement parts information.

Mark all parts during engine disassembly. All used parts must be reinstalled in their exact installation position. Parts must not be interchanged between cylinders.

If engine is equipped with Nikasil® pistons and cylinders which meet all critical dimensions, hone cylinders lightly. Replace piston rings with Gôetz® rings. If equipped with Alusil® pistons and cylinders, replace with Nikasil® pistons and cylinders.

Table a. Piston and Cylinder Identification

Manufacturer

Alloy

Cylinder

Piston

Oil control ring (groove 3)

Mahle®

Nikasil®

Coated aluminum, yellowish

Forged, leaded, dark grey

Bevelled edge, rubber lined spring, not chrome plated

KS®

Alusil®

Uncoated aluminum, light grey

Ferrocoat (cast iron coat), light grey

Double-bevelled, rubber lined spring, chrome plated

Piston weight, checking

Piston Weight Specifications

• Weight tolerance New piston: match to within 4 grams (0.14 oz.) Replacement piston: match to within 8 grams (0.28 oz.)

— Piston is weighed with wrist pin, wrist pin clips and rings installed.

Table b. Weight Classes for Mahle® Pistons

Weight class

Engine type 930/21

Code

Standard

613 - 617 g (21.46 - 21.60 oz.) 617-621 g (21.60-21.74 oz.)

permissible tolerance

621- 625 g (21.74 - 21.88 oz.) 625 - 629 g (21.88 - 22.02 oz.)

permissible tolerance

613-621 g (21.46- 21.74 oz.) 621- 629 g (21.74 - 22.02 oz.)

--or-+ or++

Table c. Weight Classes for KS® Pistons

Weight class

Engine type 930/21 USA

Code

Standard

650 - 654 g (22.75 - 22.89 oz.) 654 - 658 g (22.89 - 23.03 oz.)

permissible tolerance

658 - 662 g (23.03 - 23.17 oz.) 662 - 666 g (23.17 - 23.31 oz.)

permissible tolerance

650 - 658 g (22.75 - 23.03 oz.) 658 - 666 g (22.75 - 23.31 oz.)

— or-+ or ++

Porsche 911 Dimensions

Cylinder height, checking

^ Cylinder manufacturer identification and dimensions are indicated by marks on cylinder base.

Table d. Cylinder Height

Tolerance Group

Cylinder height

5

85.400 - 85.425 mm (3.3621 -3.3631 in.)

6

85.425 - 85.450 mm (3.3631 - 3.3641 in.)

Cylinder roundness, checking

Check cylinder roundness by measuring bore in two directions perpendicular to stud holes (A and B).

• Measure cylinder at a point 30 mm (1.181 in.) below upper edge.

Cylinder Roundness Wear Limit

• Difference between A and B 0.04 mm (0.0016 in.)

Piston and cylinder wear, checking

^ Check piston for wear by measuring across piston skirt (A).

• Measure Mahle® pistons 18 mm (0.71 in.) from bottom (B).

• Measure KS® pistons 10 mm (0.39 in.) from bottom (B).

Aluminum Nikasil Plated Cylinders

Check cylinder for wear by measuring bore 30 mm (1.18 in.) below upper edge.

— Replace cylinders if measured diameter exceeds 0.08 mm (0.0031 in.) from installed size.

— Replace pistons and cylinders if running clearance exceeds 0.12 mm (0.005 in.).

Table e. Mahle® Piston and Cylinder Sizes

Code (B)

Cylinder diameter

Piston diameter

0

95.000 - 95.007 mm (3.7401 - 3.7404 in.)

94.965 - 94.975 mm (3.7387 - 3.7391 in.)

1

95.007-95.014 mm (3.7404 - 3.7407 in.)

94.972 - 94.982 mm (3.7390 - 3.7394 in.)

2

95.014-95.021 mm (3.7407 - 3.7409 in.)

94.979 - 94.989 mm (3.7393 - 3.7397 in.)

3

95.021 - 95.028 mm (3.7409-3.7413 in.)

94.986 - 94.996 mm (3.7395-3.7399 in.)

Table f. KS® Piston and Cylinder Sizes

Code (B)

Cylinder diameter

Piston diameter

0

95.000 - 95.005 mm (3.7401 - 3.7403 in.)

94.975 - 94.980 mm (3.7391 - 3.7393 in.)

1

95.005-95.010 mm (3.7403 - 3.7405 in.)

94.980 - 94.985 mm (3.7393 - 3.7395 in.)

2

95.010-95.015 mm (3.7405 - 3.7407 in.)

94.985 - 94.990 mm (3.7395-3.7397 in.)

3

95.015-95.020 mm (3.7407 - 3.7409 in.)

94.990 - 94.995 mm (3.7397 - 3.7399 in.)

Volkswagen Piston Dimensions

Piston rings

— Check and adjust piston ring end gaps if reusing old pistons and cylinders.

Measure ring end clearance by pushing ring into bottom of cylinder to approximate height of cylinder base gasket surface (arrow).

Piston ring side and end clearance tolerances are given in Table g and Table h.

Table g. Piston Ring End Gap Clearance

Ring (groove)

Gap at installation

Wear limit

Compression (1)

0.2 - 0.4 mm (0.008 - 0.016 in.)

0.8 mm (0.031 in.)

Compression (2)

0.2 - 0.4 mm (0.008-0.016 in.)

1.0 mm (0.039 in.)

Oil control (3)

0.3-0.6 mm (0.012-0.024 in.)

2.0 mm 0.078 in.)

Table h. Piston Ring Side Clearance

Ring (groove)

Clearance

Wear limit

Compression (1)

0.070 - 0.102 mm (0.0027 - 0.0040 in.)

0.2 mm (0.0078 in.)

Compression (2)

0.040 - 0.072 mm (0.0016 - 0.0028 in.)

0.2 mm (0.0078 in.)

Oil control (3)

0.020 - 0.052 mm (0.0008 - 0.0020 in.)

0.1 mm (0.0039 in.)

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