Home » FUSO 4M4 » FUSO 4M4 – Engine – CYLINDER HEAD AND VALVE MECHANISM – Cylinder Head

FUSO 4M4 – Engine – CYLINDER HEAD AND VALVE MECHANISM – Cylinder Head

Removal: Valve cotter
<Method 1>
• Using and, remove and install the valve cotters according to the following procedure.

• Install on the cylinder head using any bolts (M8 × 1.25 mm).

• Install on using any washers and nuts (M6 × 1.0 mm).

• Set the stay to a level position.
• Adjust the retainer and the mobile nut so that the retainer holder presses down on the valve spring retainer from directly above, and fix them in place with the wing bolt.
Adjust the vertical position of the retainer holder by raising or lowering the stay using the nuts.

• Turn the handle clockwise to press down on the valve spring retainer, thus removing the valve cotter.

<Method 2>
• Place a wood piece between the valve and to protect the valve from damage.
• Using, press down on the upper retainer to remove the valve cotter.

Inspection: Valve
• If the valve is replaced after performing the following inspection, make sure to lap the valve and valve seat. (1) Stem outside diameter
• Replace the valve if the measured value is below the limit or is severely worn.

(2) Valve seat angle
• Reface the valve if the measured value is not within the standard value range.
(3) Valve margin
• Reface or replace the valve if the measured value is below the limit.

Refacing of valve
• Limit grinding to a necessary minimum.
• If the valve margin is below the limit after grinding, replace the valve.
• After grinding, make sure to lap the valve and valve seat.

• Inspection: Valve stem-to-valve guide clearance
If the clearance exceeds the specified limit, replace the defective part(s).

Replacement of valve guide
[Removal]

[Installation]
• Measure the diameter of the valve guide mounting hole in the cylinder head.
• If the measurement exceeds the specified value, select an oversized valve guide from the table below.
• Recondition the valve guide mounting hole to the diameter corresponding to the diameter of the selected oversized valve guide.

• Temporarily place the lower retainer on the cylinder head. Then, install the valve guide until contacts the lower retainer closely.

Inspection: Contact between valve and valve seat
• Before starting inspection, check that the valve and valve guide are intact.
• Apply an even coat of red lead to the valve contact surface of the valve seat.
• Strike the valve once against the valve seat. Do not rotate the valve during this operation.

•If the red lead deposited on the valve indicates a poor contact pattern, take either of the following corrective actions.

Lapping
• Perform lapping according to the following procedure.
• Apply a thin coat of lapping compound to the valve seat contact surface of the valve.
• Adding a small amount of engine oil to the lapping compound can facilitate even application.
• Start with an intermediate-grit compound (120 to 150 grit) and finish with a fine-grit compound (200 grit or more).

• Strike the valve several times against the valve seat while rotating the valve a little at a time.
• Wash away the compound with diesel fuel.
• Apply engine oil to the valve contact surface of the valve seat and rub in the valve and valve seat well.
• Inspect the contact pattern of the valve and valve seat again.
• If the contact pattern is still defective, replace the valve seat.

Inspection: Valve seats
• If a valve is corrected or replaced with a new one as a result of the following inspection, make sure to lap the valve and valve seat.
(1) Valve seat width
• If the measurement exceeds the limit, reface or replace the valve seat.

(2) Valve sinkage from cylinder head bottom surface
• Measure the sinkage with the valve seat in intimate contact.
• If the measurement exceeds the limit, adjust or replace the defective part(s).

Refacing the valve seat
• Grind the valve seat using a valve seat cutter or valve seat grinder.
• After grinding, place a piece of sandpaper approximately #400 between the cutter and valve seat and grind the valve seat lightly.
• Use a 15° or 75° cutter to cut the valve seat to a width within the standard range. If the valve seat cannot be refaced, replace the valve seat.

Replacement of valve seat
[Removal]
• The valve seats are installed by expansion fitting. To remove a valve seat, grind inside the metal stock to reduce the wall thickness, then remove the valve seat at room temperature.

[Installation]
• Measure the inside diameters of the intake and exhaust valve seat holes A and B in the cylinder head.
• If the measurement exceeds the specified value, select an oversized valve seat from the table below.
• Reface valve seats A and B to the inside diameters of the selected oversizes.

• Replace the cylinder head if defects are evident.
• Chill the valve seats thoroughly by immersing them in liquid nitrogen.
• Install the valve seat until it contacts the cylinder head closely using and (for intake valve seat) or (for exhaust valve seat).
• After installing the valve seat, lap the valve seat and valve.

Inspection: Distortion of cylinder head bottom surface
• If the distortion exceeds the specified limit, replace the cylinder head.

 

 

 

 

 

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