Workshop Manuals Factory service & repair Alfa Romeo
Alfa Romeo 145/146 Engines, 146 Bodywork and Engine Overhaul Manual (1994-2001)07 · Engine overhaul: 1.7 16V Boxer (AR33401)
07 · Engine

Checking the piston

Make
Alfa Romeo
Model
145/146 Engines, 146 Bodywork and Engine Overhaul Manual
Year
1994–2001
Section
Overhauling › Checking the piston
Engine overhaul: 1.7 16V Boxer (AR33401)Checking the piston

Maximum ovalization

X - Y = 0,02 mm

Cross-section diagram of a cylinder with piston, showing dimensions A, B, d, X, Y, and tolerances like 95÷100 and 15÷20. An asterisk (*) indicates the area for dimensional inspection.

(*) Area for dimensional inspection

Checking the piston

  1. Measure the outside diameter of the pistons and check that it is within the specified limits.
Outside diameter of pistons (mm) (1)
Class A
(Blue)		86.950 ÷ 86.960
Class B
(Pink)		86.960 ÷ 86.970
Class C
(Green)		86.970 ÷ 86.980
Class D
(Yellow)		86.980 ÷ 86.990
Class E
(White)		86.990 ÷ 87.000

(1) The outer diameter of the piston must be measured perpendicular to the gudgeon pin hole at a distance of 13.9 mm from the axis of the gudgeon pin.

Illustration showing a hand using a caliper to measure the outside diameter of a piston, with part number 1 pointing to the piston.
  • Calculate the clearance between the cylinder and piston and check that it is within the specified limits.
Clearance between cylinders - pistons
0.04 ÷ 0.06 mm
  • If the dimensions are not within tolerance, the liners should be refaced, bearing in mind that pistons in three oversizes are available as spares; therefore the diameter is to be made within the tolerances given in the "Technical Characteristics and Specifications" GROUP 00.
  • Fit the main bearings caps on the crankcase and tighten the fastening screws to the specified torque.
  • Then bore the cylinders to within the tolerances given in the "Technical Characteristics and Specifications" GROUP 00.

Grinding should be carried out so that the signs of machining are crossed with an angle of 90° ÷ 120°.

  1. Check that the difference in weight between the pistons complete with gudgeon pins and seal rings is within the specified limits.
Difference in weight between pistons
≤ 2 g
Illustration of a balance scale with two piston-like objects on the pans, labeled 1.

Checking the seal ring gap

  1. Insert the rings in the cylinder liner, check that they adhere to the whole circumference and that the gap is within the specified limits.
Ring gap
First ring0.30 ÷ 0.50 mm
Second ring0.30 ÷ 0.50 mm
Oil scraper ring0.25 ÷ 0.50 mm
Illustration showing a piston with rings being inserted into a cylinder liner, with part number 1 pointing to the piston.

Parts & tools for this job For 1994 Alfa Romeo 145/146

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