Cummins ISF3.8 cylinder head inspection and repair

In the previous article we covered the removal and installation of the engine cylinder head.

In this article we describe how to inspect and repair the cylinder head of the ISF3.8 engine.

Remove the remains of the cylinder head gasket and clean the mating surfaces.

Using a precision straight edge and a feeler gauge, check the cylinder head for warpage.

Maximum warpage:

• longitudinal: 0.305 mm;
• transverse: 0.076 mm.

If necessary, the cylinder head, cylinder block or both may be ground by 0.5 mm. After grinding, install a repair cylinder head gasket.

The cylinder head may be ground if the valve installation depth and injector protrusion remain within tolerance. If not, replace the cylinder head.

Using a dial indicator, determine the injector protrusion at its highest point above the cylinder head mating surface.

Note: before measuring injector protrusion, install the rocker cover and injectors on the cylinder head.

Injector protrusion:

• minimum: 1.94 mm;
• maximum: 2.47 mm.

If injector protrusion differs from the nominal value, check the sealing washer thickness. Nominal thickness: 2.5 mm.

If the sealing washer thickness is correct, check for dirt and foreign particles in the injector bore. Make sure no sealing washer is stuck inside the bore. Do not adjust injector protrusion by stacking several washers. If injector protrusion is correct, remove the injector.

Using a dial indicator, check the valve installation depth in the cylinder head.

Note: when measuring valve installation depth, take two measurements at opposite points. Do not measure the depth at the centre of the valve.

Valve installation depth:

Inlet:

• minimum: 0.584 mm;
• maximum: 1.092 mm.

Exhaust:

• minimum: 0.965 mm;
• maximum: 1.473 mm.

Note: the valve installation depth may be slightly increased after lapping.

Dismantling the cylinder head

1. Mark the valves in accordance with their installation positions.

2. Compress the valve springs with the special tool (No. 4918866).

3. Install the puller screw (4) above the injector bore and insert the bolt (5) into the holes of the clamp screw removed from the cylinder head. Tighten the bolts (5). Tightening torque: 5 N·m.
4. Apply anti-seize compound to the thread of the puller screw (4). Be sure to read and follow the precautions on the label.
5. The valves are at different distances from the injector bore. The slots in the plate of the valve spring compression tool must be aligned with these springs.
6. Install the valve spring compression tool plate (1) on the puller screw (4) and align the slots in this plate with the valve springs.

7. Install the washer (3) and nut (2) on the puller screw (4). Turn the nut (2) clockwise to compress the valve springs.

Caution! The valve springs are compressed and may fly out during removal. Wear safety goggles.

8. Continue turning the nut (2) clockwise until the valve collets can be removed, for example with a magnetised screwdriver.

9. Remove the collets and the valve spring compression tool.

10. Remove the retainers and valve springs.
11. Remove the valves. Keep the removed parts in the order corresponding to the places from which they were removed so that they can be installed in their original positions.

12. Remove the valve stem seals.
13. If necessary, remove the valve seats.
    • a) The valve seat has a groove for the valve seat puller, which is made in the form of a sliding hammer. If there is no groove, machine it with a special tool (No. 3376405).

• Using an inertia puller and an adapter (No. 3165170), remove the valve seat. The assembled valve seat puller must be installed strictly perpendicular to the cylinder head.
• Insert the puller into the valve seat and turn the T-handle clockwise so that the puller slightly compresses the seat.
• Install the puller into the groove of the valve seat.
• Turn the T-handle so that the puller is under the valve insert.
• Striking the sliding hammer against the upper nut, remove the valve seat.
• Turn the T-handle anticlockwise to release the seat from the puller.

Cleaning the cylinder head

1. Clean the injector bore.
2. Clean the valve stem guide with a soft brush.

3. If necessary, remove deposits from the cooling passages.

Note: deposits can be removed in an acid tank after first removing the expansion plugs.

4. Clean the mating surface with solvent and an abrasive stone.
5. Make sure there are no nail-detectable wear marks within 3.2 mm of the combustion chamber edge. Wear outside this area does not affect combustion chamber sealing, and the cylinder head can be reused.

6. Remove carbon deposits from the valve well with a high-quality wire brush held in a drill chuck or grinder attachment.
7. Use a wire brush and solvent to remove deposits from the holes in the valve seats. Dry with compressed air.
8. Finally clean the cylinder head:
   • a) wash the cylinder head with hot soapy water;
   • b) rinse the cylinder head with clean water;
   • c) dry the cylinder head with compressed air.

Checking the cylinder head

Check the cylinder head for cracks. Carefully inspect the following areas:

• injector bore;
• combustion chamber surface;
• valve seats;
• valve guides.

Replace the cylinder head if deep cracks are present. Small and shallow cracks are acceptable.

1. Measure the diameter of the valve seat bore in the cylinder head if the seat was removed. Valve seat bore diameter: 34.837–34.863 mm.

If the diameter is greater than specified, bore the valve seat bore to the repair size (0.254 mm or 0.508 mm).

2. Measure the internal diameter of the valve guides. Valve guide internal diameter: 7.027–7.077 mm.

Replace the cylinder head if valve guide bore wear exceeds the standard or valve guide damage is found.

Checking the valves

1. Clean the valve heads with a circular soft wire brush.

2. Polish the valve stems with an abrasive sponge (3823258) using solvent.

3. Check the valves for excessive wear of the head, stem and stem tip, as well as for bending and deformation.

4. Check the valves for damage to the collet grooves.

5. Measure the valve stem diameter at three points at the following distances: A — 40 mm, B — 90 mm, C — 140 mm. Valve stem diameter: 6.96–7.01 mm.

Checking the valve springs

1. Using a metal square (90°), check the out-of-squareness of the valve spring as shown in the figure. Maximum permissible out-of-squareness: 1.5 mm.

2. Using a vernier calliper, measure the spring length in the free state. Nominal free length of the spring: 47.75 mm. If the spring length differs from the nominal value, replace the valve spring.
3. Measure the valve spring length under load. Nominal spring length (at 320.8–358.8 N): 35.33 mm.

4. Check the cylinder head mounting bolts. Check the free length of the bolt shank. Maximum bolt length: 152.1 mm. If the bolt length exceeds the maximum, replace the bolt. A gauge (No. 3164057) can be used for checking.

Assembling the cylinder head

Install new valve seats. Note: valve seats must not be reused.

Installing the valve seats

When installing, note that the inlet and exhaust valve seats are different. Valve seat angle:

• inlet: 30°;
• exhaust: 45°.

Use a new valve for each inlet and exhaust valve seat, pressing it in; if this cannot be done, use a special hammer to install the new valve seat inserts.

Lap the valves to their seats.

• a) Before installation, lubricate the valve stems with SAE 15W-40 engine oil.
• b) Apply a thin even layer of fine lapping abrasive (23375805 or similar) to the valve head.
• c) Using an electric or manual lapping tool, apply force to the centre of the valve.
• d) Turn the valve clockwise and anticlockwise. Continue lapping until reliable contact between the seat and the valve is achieved.
• e) Remove the lapping abrasive.

• f) Check the valve head thickness. Minimum valve head thickness: 0.79 mm. If the thickness is less than the minimum, replace the valve.

1. Install the valves, lubricating their stems with engine oil. When installing previously removed valves, install them in the places from which they were removed.
2. Install new valve stem seals. Install seals of the same type and colour as those previously installed. Colours used:
   • green — exhaust valves;
   • yellow — inlet valves;
   • brown — inlet and exhaust valves.
3. Lubricate the valve stem seals with engine oil. Using a drift, install the new valve stem seals. Hold the valve by hand during installation.
4. Install the retainers and valve springs.

5. Install the collets. Compress the valve springs with the special tool (No. 4918866).
6. Install the puller screw (4) above the injector bore and insert the bolt (5) into the hole of the clamp screw removed from the cylinder head. Tighten the bolts (5). Tightening torque: 5 N·m.

7. Apply anti-seize compound to the thread of the puller screw (4).
8. Note: the valves are at different distances from the injector bore. It is important to align the slots in the plate of the valve spring compression tool with these springs.
9. Install the valve spring compression tool plate (1) on the puller screw (4) and align the slots in this plate with the valve springs.
10. Install the washer (3) and nut (2) on the puller screw (4).

11. Compress the valve springs and install the collets.

Note: apply assembly grease (No. 3163087 or similar) to the collets to make it easier to hold them in place until the valve spring compression tool is removed.

12. Remove the valve spring compression tool.

13. Tap the valve ends with a plastic-headed hammer to ensure reliable retention by the collets.

Dismantling the rocker arms

Note: install the rocker arm parts in the places from which they were removed.

1. Remove the rocker arms from the support.

2. Remove the shafts from the rocker arms.

3. Do not remove the bush from the end of the rocker arm. If it is damaged, replace the rocker arm.

4. Unscrew the locknut and adjusting screw.

Checking the rocker arms

1. Measure the internal diameter of the rocker arm bore. Maximum diameter: 22.027 mm.

2. Measure the external diameter of the rocker arm shaft. Minimum diameter: 21.965 mm.

Assembling the rocker arms

Note: all rocker arm parts must be installed in the places from which they were removed.

1. Screw the adjusting screws in fully, then screw in the locknut.
2. Lubricate the rocker arm shafts with engine oil.

3. Install the shafts in the rocker arms.
4. Install the rocker arms on the support.

Note: do not confuse the inlet and exhaust valve rocker arms.

5. Install the valve bridges in the places from which they were removed.
6. Install the rocker arms with supports assembled in the places from which they were removed.
7. Screw in the support mounting bolts. Tightening torque: 36 N·m.