Connecting Rod and Piston Ring – Inspect and adjust


Inspect the Piston and the Piston Rings

Check the piston for wear and other damage.
Check that the piston rings are free to move in the grooves and that the rings are not broken.

Inspect the Clearance of the Piston Ring

Remove the piston rings and clean the grooves and the piston rings.

(1) Feeler gauge (2) Piston ring (3) Piston grooves

Fit new piston rings (2) in the piston grooves (3).
Check the clearance for the piston ring by placing a suitable feeler gauge (1) between piston groove (3) and the top of piston ring (2).

Inspect the Piston Ring End Gap


(1) Piston ring (2) Cylinder ring ridge (3) Feeler gauge

Clean all carbon from the top of the cylinder bores.
Place each piston ring (1) in the cylinder bore just below the cylinder ring ridge (2). Use a suitable feeler gauge (3) to measure piston ring end gap.  The coil spring must be removed from the oil control ring before the gap of the oil control ring is measured.

Connecting Rod Inspect

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
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.
• New piston pin bearings must be bored after installation in the original connecting rods
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 Table for each grade of length of connecting rod. In order to ensure that the piston height above the cylinder block is correct, three grades of connecting rods “F” to “L” are used during manufacture at the factory. Replacement connecting rods are available in three grades. These grades of connecting rod are “F” to “L”. 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 “F”. The shortest grade is marked with the letter “L”. The difference in length between each grade of connecting rods is the following value: 0.076 mm (0.0030 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. 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

If the piston pin bearing requires replacement but the original connecting rod is not replaced, the following procedures must be performed:
Determine the grade of length of the connecting rod. Use one of the following characteristics:
• The mark
• The color
• Measuring the length
Ensure that the connecting rod is aligned parallel and that the connecting rod is not distorted.
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.  Surface finish of the bored hole in the piston pin bearing ....... Ra 0.8 micrometers.


Machine the ends of the piston pin bearing to the correct length. Remove any sharp edges.
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. Do not stamp a new letter on the connecting rod. The force of stamping may damage the connecting rod.

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:

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

Use the following tools in order to measure the length of the connecting rod:
• Appropriate gauges for measuring distance
• Measuring pins (1)
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.

Distortion of The Connecting Rod

Use the following tools in order to measure the distances for the connecting rod (2) which are specified in illustration:
• Appropriate gauges for measuring distance
• Measuring pins (1)

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.

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 ± 0.03mm(8.625 ± 0.001 inch).
Inspect the piston pin bearing and the piston pin for wear.
Measure the clearance of the piston pin in the piston pin bearing.