C4.4 Engines for Caterpillar Built Machines Connecting Rod - Inspect Caterpillar


Connecting Rod - Inspect
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1.1. Length of The Connecting Rod
2.2. Piston Pin Bearings
3.2. Measure The Length Of The Connecting Rod
4.1. Distortion of The Connecting Rod

These procedures determine the following characteristics of the connecting rod:

  • The length of the connecting rod

  • The distortion of the connecting rod

  • The parallel alignment of the bores of the connecting rod

Note: If the crankshaft or the cylinder block are replaced, the piston height for all cylinders must be measured. The grade of length of the connecting rods may need to be changed in order to obtain the correct piston height.

If the grade of length must be changed, one of the following actions must be taken:

  • New connecting rod assemblies that are the correct grade of length must be installed. Refer to "Length of The Connecting Rod".

  • New piston pin bearings must be bored after installation in the original connecting rods. Refer to "Piston Pin Bearings".

Note: When the piston pin is installed, always install new retaining rings on each end of the piston pin. If the piston pin cannot be removed by hand, heat the piston to a temperature of 45° ± 5 °C (113° ± 9 °F) in order to aid the removal of the piston pin. Heating the piston to this temperature may also aid the installation of the piston pin.

Length of The Connecting Rod

The connecting rod length (CRL) is the length of the connecting rod. Refer to Specifications, "Connecting Rod" for more information about the different grades of connecting rods.

In order to ensure that the piston height above the cylinder block is correct, six grades of connecting rods are used during manufacture at the factory. Replacement connecting rods are available in six grades. The grade of length is identified by a letter or a color which is marked on the side of the connecting rod. The longest grade is marked with the letter "R". The shortest grade is marked with the letter "B". The difference in length between each grade of connecting rods is the following value: 0.046 mm (0.0018 inch)

The grade of length of a connecting rod is determined in the factory by machining an eccentric hole in a semi-finished piston pin bushing. Therefore, the grade of length is determined by the position of the center of the hole in the piston pin bearing.

If the connecting rod must be replaced, a new connecting rod assembly must be purchased and installed. Refer to Specifications, "Connecting Rod" for more information about the different grades of connecting rods.

A new piston pin bearing is installed in the new connecting rod at the factory. The bore of the piston pin bearing is reamed to the correct eccentricity.

Piston Pin Bearings

Note: This procedure requires personnel with the correct training and the use of specialized equipment for machining.

If the piston pin bearing requires replacement but the original connecting rod is not replaced, the following procedures must be performed:

  1. Determine the grade of length of the connecting rod. Use one of the following characteristics:

    • The mark

    • The color

    • Measuring the length

  2. Ensure that the connecting rod is aligned parallel and that the connecting rod is not distorted. Refer to "Distortion of The Connecting Rod" in this service module.

  3. Remove the piston pin bearing from the connecting rod. Install a new bearing in the connecting rod. The new bearing is partially finished. The new bearing must be bored off-center to the correct diameter. This off-center position is determined by the grade of length of the connecting rod. The correct diameter of the bore in the piston pin bearing is given in the Specifications, "Connecting Rod".

    Surface finish of the bored hole in the piston pin bearing ... Ra 0.8 micrometers

  4. Machine the ends of the piston pin bearing to the correct length. Remove any sharp edges. Refer to Specifications, "Connecting Rod".

  5. If the grade of length of the connecting rod is changed, the letter that is stamped on the connecting rod must be removed. Etch a letter that is for the new grade of length on the side of the connecting rod.

    Note: Do not stamp a new letter on the connecting rod. The force of stamping may damage the connecting rod.

Refer to Specifications, "Connecting Rod" for more information about the different grades of connecting rods.

Measure The Length Of The Connecting Rod

If the mark or the color of the grade of length cannot be observed on the connecting rod, perform the following procedure:



Illustration 1g00326546
Measure the length of the connecting rod.
(1) Measuring pins
(2) Connecting rod
(CRL) Connecting Rod Length

  1. Refer to Illustration 1. Use the following tools in order to measure the length of the connecting rod:

    • Appropriate gauges for measuring distance

    • Measuring pins (1)

  2. Ensure that the measuring pins (1) are parallel. "CRL" is measured when the bearing for the crankshaft journal is removed and the original piston pin bearing is installed.

    Measure "CRL". Compare the "CRL" that is provided. Refer to Specifications, "Connecting Rod". The grade of length of the connecting rod is determined by the "CRL". Refer to Specifications, "Connecting Rod" for the correct grade of length.

Distortion of The Connecting Rod

  1. Use the following tools in order to measure the distances for the connecting rod (2) which are specified in Illustration 1:

    • Appropriate gauges for measuring distance

    • Measuring pins (1)


    Illustration 2g00326423
    Measure the connecting rod for distortion.
    (1) Measuring pins
    (2) Connecting rod
    (L) The length between the centers of the piston pin bearing and the crankshaft journal bearing is shown in Illustration 2.

  2. Refer to illustration 2. Measure the connecting rod for distortion and parallel alignment between the bores.

    The bores for the crankshaft bearing and the bearing for the piston pin must be square and parallel with each other within the required limits. If the piston pin bearing is removed, the limit "L" is the following value: ± 0.25 mm (± 0.010 inch)

    The limits are measured at a distance of 127 mm (5.0 inch) from each side of the connecting rod.

    If the piston pin bearing is not removed, the limit "L" is the following value: ± 0.06 mm (± 0.0024 inch)

    L is equal to 219.08 ± 0.03 mm (8.625 ± 0.001 inch).

  3. Inspect the piston pin bearing and the piston pin for wear.

  4. Measure the clearance of the piston pin in the piston pin bearing. Refer to the Specifications Module, "Connecting Rod" for dimensions.

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