Repair of the connecting rod-piston group Cummins ISF3.8

Repair of the piston-connecting rod assembly of the Cummins ISF3.8 engine

Turn the crankshaft so that the pistons are below the carbon deposit zone located above the piston ring travel zone.

To remove carbon deposits, use a fine-grained abrasive stone with a fibrous structure and a solvent.

Mark the cylinder number on the piston crown.

Removal of the piston-connecting rod assembly

Set the piston to BDC by turning the crankshaft.

Mark the connecting rod and cap with the cylinder number.
Loosen (but do not remove) the connecting rod bolts.

Fig. 3. Loosening the connecting rod bolts.

Tap the connecting rod bolts with a rubber-headed hammer to release the caps.
Remove the connecting rod bolts.

Fig. 4. Removal of the connecting rod bolts.

Remove the connecting rod cap.
Remove the lower connecting rod bearing shell.

Removal of the cap and shell — Fig. 5. Removal of the connecting rod cap and lower shell.

Mark the cylinder number and a letter on the flat surface of the lower connecting rod bearing shell.

Marking the shell — Fig. 6. Marking the lower connecting rod bearing shell.

Using the hammer handle, push the piston with the connecting rod out of the cylinder. Be careful not to damage the connecting rod or the crankshaft journal surface.

Fig. 7. Withdrawing the piston from the cylinder.

Remove the upper connecting rod bearing shell.
Mark the flat surface of the upper connecting rod bearing shell.

Dismantling of the piston-connecting rod assembly

Fig. 8. Removal of the piston rings with a spreader.

Remove the piston rings with a spreader.

Extract the circlips.

Remove the gudgeon pin (at room temperature) and the connecting rod.

Inspection of the piston-connecting rod assembly parts

Measure the piston skirt diameter 12 mm from its lower edge.

Piston diameter:

nominal: 101.864–101.887 mm;
repair (0.5 mm): 102.364–102.387 mm;
repair (1.0 mm): 102.864–102.887 mm.

Checking the groove clearance — Fig. 12. Checking the clearance between the piston ring and the groove.

Check the clearance between the piston ring and the piston ring groove.

Clearance between the groove and the piston ring:

lower compression ring: 0.04–0.11 mm;
oil scraper ring: 0.04–0.085 mm.

Measuring the boss diameter — Fig. 13. Measuring the internal diameter of the gudgeon pin bosses.

Measure the internal diameter of the gudgeon pin bosses. Boss diameter: 42.006–42.012 mm.

Fig. 14. Measuring the gudgeon pin diameter.

Measure the gudgeon pin diameter. Gudgeon pin diameter: 39.997–40.003 mm.

Measuring the con-rod bush — Fig. 15. Measuring the internal diameter of the connecting rod small end bush.

Measure the internal diameter of the connecting rod small end bush. Bush diameter: 40.019–40.042 mm.

If the bush dimensions do not correspond to the nominal values or it is damaged, replace the connecting rod assembly.

Checking the big end — Fig. 16. Checking the connecting rod big end.

Check the connecting rod big end (with shells removed):

Lubricate the connecting rod bolts with clean engine oil.
Install the cap and bolts with washers on the connecting rod.
Tighten the bolts.
Use a bore gauge to measure the internal diameter within 20 degrees of each part of the parting line.

Measuring the con-rod bore — Fig. 17. Measuring the diameter of the bore for the crankshaft journal.

Measure the internal diameter in the direction perpendicular to the parting line.

Diameter of the bore for the crankshaft journal in the connecting rod with the bearing removed: 72.99–73.01 mm.

If the values differ from those specified, replace the connecting rod.

Checking with shells installed — Fig. 18. Checking the connecting rod big end with shells installed.

Check the connecting rod big end (with shells installed). Repeat the check described above after installing the bearing in the connecting rod.

Diameter of the bore for the crankshaft journal in the connecting rod with the bearing installed:

nominal: 68.905–69.10 mm;
repair (0.25 mm): 68.80–68.85 mm;
repair (0.50 mm): 68.55–68.60 mm.

Checking the ring end gap — Fig. 19. Installing the piston ring in the cylinder to check the end gap.

Check the piston ring end gap.

Using the piston, push the ring to a depth (A) of 89 mm from the top surface of the cylinder block so that the ring plane is perpendicular to the cylinder surface.

Measuring the end gap — Fig. 20. Measuring the piston ring end gap.

Using a feeler gauge, determine the piston ring end gap.

Gap:

1st compression ring: 0.29–0.58 mm;
2nd compression ring: 0.88–1.37 mm;
oil scraper ring: 0.28–0.77 mm.

If the ring end gap does not correspond to the nominal:

make sure the ring type corresponds to the catalogue number;
check the cylinder bore diameter;
make sure the ring end gap was measured at a depth of 50 mm from the top surface of the cylinder block;
install another set of rings.

Assembly of the piston-connecting rod assembly

Install the circlip on one side of the piston.
Lubricate the pin and its seats with engine oil.
Install the piston on the connecting rod with the marks towards the front of the engine.

Note:

The connecting rod has three notches which must be directed towards the front of the engine.

Fig. 21. Marks on the connecting rod (three notches).

There is an arrow on the piston crown which must be directed towards the front of the engine.

Install the gudgeon pin at room temperature (the pistons do not need to be heated).
Install the circlip on the opposite side.
Install the piston rings.
Using a spreader, install the compression rings with the marks upwards.

Fig. 23. Installing the piston rings with a spreader.

Install the oil scraper ring so that the expander spring gap is opposite the scraper end gap.

Fig. 24. Installing the oil scraper ring.

Note: the installation position of the rings is determined by their profile.

Fig. 25. Piston ring profiles: 1 — upper compression ring; 2 — lower compression ring; 3 — oil scraper ring.

Installation of the piston-connecting rod assembly

Clean the cylinder block before installing the piston-connecting rod assembly.
Install the connecting rod bearing shells.
Note: the removed connecting rod bearing shells must be installed in the places from which they were removed. Make sure there is no dirt or foreign particles on the connecting rods and on the back of the shells. Do not lubricate the back of the connecting rod bearings or the connecting rod big end.
Install the upper shell in the connecting rod. The shell tab must engage in the connecting rod groove. The shell edge must be flush with the surface under the cap.
If the engine is fitted with fractured big end connecting rods, the lower and upper bearing shells are not interchangeable.
Install the piston-connecting rod assembly in the cylinder block.
Apply assembly grease to the working surface of the shell.

Fig. 26. Applying grease to the shell working surface.

Lubricate the cylinder wall with clean engine oil.

Lubricate the piston rings and piston skirts with clean engine oil.
Turn the rings, positioning their end gaps as shown in the figure. The end gap of each ring must not be opposite the gudgeon pin or the end gaps of other rings.

Piston ring end gap positions — Fig. 28. Correct positions of the piston ring end gaps.

Incorrect positioning of the ring end gaps will cause loss of cylinder sealing.

Compress the piston rings with a special tool.

Fig. 29. Compressing the piston rings with the tool.

Turn the crankshaft and set the connecting rod journal of the required cylinder to BDC.

Setting the con-rod journal to BDC — Fig. 30. Setting the connecting rod journal to BDC.

Install the piston-connecting rod assembly in the cylinder with the “Front” mark/arrow towards the front of the engine. The long part of the connecting rod big end (1) and the notch (2) of the piston skirt must be on the exhaust side. If not, make sure the piston and connecting rod are assembled correctly.

Piston orientation — Fig. 31. Orientation of the piston and connecting rod in the cylinder.

Tap the tool with a hammer so that there is no gap between the cylinder block mating face and the lower part of the tool clamp. Move the piston until the upper ring has fully entered the cylinder.

Fig. 32. Installing the piston in the cylinder.

Guiding by hand from below, install the piston-connecting rod assembly until it contacts the connecting rod journal.
Install the shell in the connecting rod cap. The shell tab must engage in the cap groove.

Installing the shell in the cap — Fig. 33. Installing the shell in the connecting rod cap.

Lubricate the shell working surface with assembly grease (No. 3163087). Do not apply grease to the back of the shell!
The numbers on the connecting rod and cap must be the same, and the piston must be installed in the corresponding cylinder. The numbers on the connecting rod and connecting rod cap must be on the same side of the connecting rod to reduce the risk of engine damage during operation.
Install the cap and connecting rod bolts.
Tighten the connecting rod bolts. Tightening torques:
- first stage — 30 N·m;
- second stage — 60 N·m;
- third stage — turn a further 60° clockwise.

Fig. 34. Measuring the side clearance between the connecting rod and the crank web.

Measure the side clearance between the connecting rod and the crankshaft crank web. Side clearance: 0.125–0.275 mm.
Measure the piston protrusion above the cylinder block surface.
Note: this operation is necessary after repair or replacement of the piston, crankshaft, connecting rod or cylinder block.

Fig. 35. Installing the dial indicator to measure piston protrusion.

Install the dial indicator on the cylinder block surface and set it to “0”.
Move the dial indicator directly over the gudgeon pin, avoiding transverse deflection. Do not touch the plated surface with the indicator plunger.
Set the piston to TDC.
Turning the crankshaft in both directions, determine the maximum protrusion. Record the measurement results.

Measuring piston protrusion — Fig. 36. Measuring the piston protrusion.

Piston protrusion: 0.151–0.485 mm.

Recording the measurement results — Fig. 37. Recording the piston protrusion measurement results.

If the piston protrusion does not meet the standard, check the correct selection of the installed parts and/or the machining of the top surface of the cylinder block.
Turn the crankshaft and make sure it turns freely.