Service Limit: 0.05 mm (0.002 in.)

If the cylinder head is warped more than the service limit, replace it.

If the cylinder head is warped less than the service limit, repair the head by rubbing the lower surface on emery paper secured to a surface plate (first No. 200, then No. 400).

 

Valve Clearance Inspection

• Refer to the Valve Clearance Inspection in the Periodic Maintenance chapter.

Valve Clearance Adjustment

• Refer to the Valve Clearance Adjustment in the Periodic Maintenance chapter.

Valve Removal

• Remove cylinder head (see Cylinder Head Removal).

• Remove the valve lifter and shim.

○Mark and record the valve lifter and shim locations so they

can be installed in their original positions.

• Using the valve spring compressor assembly, remove the valve.

Special Tools - Valve Spring Compressor Assembly [A]:

57001-241

Valve Spring Compressor Adapter, 21 [B]: 57001-1272

Valve Installation

• Replace the oil seal with a new one.

○Apply engine oil to the oil seal lip.

• Apply a thin coat of molybdenum disulfide grease to the valve stem before valve installation.

• Install the springs so that the closed coil end faces down-

wards (the side painted in green faces upwards).

Valve Stem [A] Oil Seal [B] Spring Seat [C]

Closed Coil End [D] Valve Spring [E]

Side Painted in Green [F] Retainer [G]

Split Keepers [H]

Valve Guide Removal

• Remove:

Valve (see Valve Removal)

Oil Seal Spring Seat

• Heat the area around the valve guide to 120 ~ 150°C (248

~ 302°F), and hammer lightly on the valve guide arbor [A]

CAUTION

Do not heat the cylinder head with a torch. This will warp the cylinder head. Soak the cylinder head in oil and heat the oil.

to remove the guide from the top of the head.

Special Tool - Valve Guide Arbor, 4.5: 57001-1331

 

Valve Guide Installation

• Apply engine oil to the valve guide outer surface before installation.

• Heat the area around the valve guide hole to about 120 ~

150°C (248 ~ 302°F).

• Drive the valve guide in from the top of the head using the valve guide arbor. The flange stops the guide from going

in too far.

Special Tool - Valve Guide Arbor, 4.5: 57001-1331

• Wait until the cylinder head cools down and then ream the valve guide with the valve guide reamer [A] even if the old

guide is reused.

○Turn the reamer in a clockwise direction until the reamer

turns freely in the guide. Never turn the reamer counter-

clockwise or it will be dulled.

○Once the guides are reamed they must be cleaned thor-

oughly.

Special Tool - Valve Guide Reamer, 4.5: 57001-1333

Valve-to-Guide Clearance Measurement (Wobble Method)

If a small bore gauge is not available, inspect the valve guide wear by measuring the valve to valve guide clearance with the wobble method as indicated below.

• Insert a new valve [A] into the guide [B] and set a dial

gauge against the stem perpendicular to it as close as

possible to the cylinder head mating surface.

• Move the stem back and forth [C] to measure valve/valve guide clearance.

• Repeat the measurement in a direction at a right angle to

the first.

If the reading exceeds the service limit, replace the guide.

 

NOTE

○The reading is not actual valve/valve guide clearance

because the measuring point is above the guide.

Valve/Valve Guide Clearance (Wobble Method) Standard:

Exhaust 0.07 ~ 0.14 mm (0.0028 ~ 0.0055 in.)

Inlet 0.02 ~ 0.08 mm (0.0008 ~ 0.0032 in.)

Service Limit:

Exhaust 0.27 mm (0.0106 in.)

Inlet 0.22 mm (0.0087 in.)

 

Valve Seat Inspection

• Remove the valve (see Valve Removal).

• Check the valve seating surface [A] between the valve [B]

and valve seat [C].

○Measure the outside diameter [D] of the seating pattern

on the valve seat.

If the outside diameter is too large or too small, repair the seat (see Valve Seat Repair).

Valve Seating Surface Outside Diameter Standard:

Exhaust 27.6 ~ 27.8 mm (1.087 ~ 1.094 in.)

Inlet 32.6 ~ 32.8 mm (1.283 ~ 1.291 in.)

○Measure the seat width [E] of the portion where there is no build-up carbon (white portion) of the valve seat with a vernier caliper.

Good [F]

If the width is too wide [G], too narrow [H] or uneven [J], repair the seat (see Valve Seat Repair).

Valve Seating Surface Width Standard:

Exhaust 0.5 ~ 1.0 mm (0.020 ~ 0.039 in.)

Inlet 0.5 ~ 1.0 mm (0.020 ~ 0.039 in.)

Valve Seat Repair

• Repair the valve seat with the valve seat cutters [A].

Special Tools - Valve Seat Cutter Holder Bar [C]: 57001-1128

Valve Seat Cutter Holder, 4.5 [B]: 57001-1330

For Exhaust Valve Seat

Valve Seat Cutter, 45° - 30: 57001-1187

Valve Seat Cutter, 32° - 30: 57001-1120

Valve Seat Cutter, 60° - 30: 57001-1123

For Inlet Valve Seat

Valve Seat Cutter, 45° - 35: 57001-1116

Valve Seat Cutter, 32° - 35: 57001-1121

Valve Seat Cutter, 55° - 35: 57001-1247

If the manufacturer’s instructions are not available, use the following procedure.

 

 

Seat Cutter Operation Care

1. This valve seat cutter is developed to grind the valve for repair. Therefore the cutter must not be used for other purposes than seat repair.

2. Do not drop or shock the valve seat cutter, or the dia- mond particles may fall off.

3. Do not fail to apply engine oil to the valve seat cutter before grinding the seat surface. Also wash off ground particles sticking to the cutter with washing oil.

NOTE

○Do not use a wire brush to remove the metal particles

from the cutter. It will take off the diamond particles.

4. Setting the valve seat cutter holder in position, operate the cutter in one hand. Do not apply too much force to the diamond portion.

NOTE

○Prior to grinding, apply engine oil to the cutter and dur-

ing the operation, wash off any ground particles sticking

to the cutter with washing oil.

5. After use, wash it with washing oil and apply thin layer of engine oil before storing.

Marks Stamped on the Cutter

The marks stamped on the back of the cutter [A] represent the following.

60°........................... Cutter angle [B]

37.5....................... Outer diameter of cutter [C]

 

Operating Procedures

• Clean the seat area carefully.

• Coat the seat with machinist’s dye.

• Fit a 45° cutter into the holder and slide it into the valve

guide.

CAUTION

Do not grind the seat too much. Overgrinding will reduce valve clearance by sinking the valve into the head. If the valve sinks too far into the head, it will be impossible to adjust the clearance, and the cylin- der head must be replaced.

• Press down lightly on the handle and turn it right or left. Grind the seating surface only until it is smooth.

 

 

• Measure the outside diameter of the seating surface with a vernier caliper.

If the outside diameter of the seating surface is too small, repeat the 45° grind until the diameter is within the spec- ified range.

Widened Width [A] of engagement by machining with 45° cutter

Ground Volume [B] by 32° cutter 32° [C]

Correct Width [D]

Ground Volume [E] by 60° or 55° cutter 60° or 55° [F]

• Measure the outside diameter of the seating surface with a vernier caliper.

If the outside diameter of the seating surface is too small, repeat the 45° grind [A] until the diameter is within the specified range.

Original Seating Surface [B]

NOTE

○Remove all pittings of flaws from 45° ground surface.

○After grinding with 45° cutter, apply thin coat of machin-

ist’s dye to seating surface. This makes seating surface

distinct and 32° and 60° (or 55°) grinding operation eas- ier.

○When the valve guide is replaced, be sure to grind with

45° cutter for centering and good contact.

If the outside diameter [A] of the seating surface is too large, make the 32° grind described below.

If the outside diameter of the seating surface is within the specified range, measure the seat width as described be- low.

• Grind the seat at a 32° angle [B] until the seat outside

diameter is within the specified range.

○To make the 32° grind, fit a 32° cutter into the holder, and

slide it into the valve guide.

○Turn the holder one turn at a time while pressing down

CAUTION

The 32° cutter removes material very quickly. Check the seat outside diameter frequently to pre- vent overgrinding.

very lightly. Check the seat after each turn.

○After making the 32° grind, return to the seat outside di- ameter measurement step above.

• To measure the seat width, use a vernier caliper to mea-

sure the width of the 45° angle portion of the seat at sev-

eral places around the seat.

If the seat width is too narrow, repeat the 45° grind until the seat is slightly too wide, and then return to the seat outside diameter measurement step above.

 

 

If the seat width is too wide, make the 60° or 55° [A] grind described below.

If the seat width is within the specified range, lap the valve to the seat as described below.

• Grind the seat at a 60° or 55° angle until the seat width is

within the specified range.

○To make the 60° or 55° grind, fit 60° or 55° cutter into the

holder, and slide it into the valve guide.

○Turn the holder, while pressing down lightly.

○After making the 60° or 55° grind, return to the seat width

measurement step above.

Correct Width [B]

• Lap the valve to the seat, once the seat width and outside diameter are within the ranges specified above.

○Put a little coarse grinding compound on the face of the

valve in a number of places around the valve head.

○Spin the valve against the seat until the grinding com-

pound produces a smooth, matched surface on both the

seat and the valve.

○Repeat the process with a fine grinding compound.

Lapper [A]

Valve Seat [B] Valve [C]

• The seating area should be marked about in the middle

of the valve face.

If the seat area is not in the right place on the valve, check to be sure the valve is the correct part. If it is, it may have been refaced too much; replace it.

• Be sure to remove all grinding compound before assem-

bly.

• When the engine is assembled, be sure to adjust the valve clearance (see Valve Clearance Adjustment in the Peri-

odic Maintenance chapter).

 

 

 

Cylinder Removal

• Remove:

Cylinder Head (see Cylinder Head Removal)

Front Engine Mounting Bolts (Both Side) [A] (see Engine Removal in the Engine Removal/Installation chapter) Front Engine Brackets (Both Side) [B] (see Engine Re- moval in the Engine Removal/Installation chapter) Cylinder [C]

 

Cylinder Installation

NOTE

○If a new cylinder is used, use new piston ring.

• Install the dowel pins [A] and new cylinder gasket [B].

 

• The piston ring openings must be positioned as shown in the figure. The openings of the oil ring steel rails must be

about 30 ~ 40° of angle from the opening of the top ring. Top Ring [A]

Second Ring [B]

Oil Ring Steel Rails [C] Oil Ring Expander [D] Hollow [E]

30 ~ 40° [F]

 

• Apply molybdenum disulfide oil solution to the cylinder bore, piston rings and piston.

• Prepare two auxiliary head bolts with their head cut.

○Install the two bolts [A] diagonally in the crankcase.

• Position the crankshaft so that all the piston heads are almost level.

• Install the cylinder block.

○Insert the piston rings with your thumbs.

 

 

Piston Removal

• Remove the cylinder (see Cylinder Removal).

• Place a clean cloth under the pistons and remove the pis-

ton pin snap ring [A] from the outside of each piston.

 

• Remove the piston pins.

Special Tools - Piston Pin Puller [A]: 57001-1568

Piston Pin Puller Adapter C [D]: 57001-1657

Center Bolt [B] Shall of Piston [C]

• Remove the pistons.

 

 

• Carefully spread the ring opening with your thumbs and then push up on the opposite side of the ring [A] to remove

it.

• Remove the 3-piece oil ring with your thumbs in the same manner.

 

 

Piston Installation

• Install the oil ring expander [A] in the bottom piston ring groove so the ends [B] butt together.

• Install the oil ring steel rails, one above the expander and

one below it.

○Spread the rail with your thumbs, but only enough to fit

the rail over the piston.

○Release the rail into the bottom piston ring groove.

NOTE

○The oil ring rails have no “top” or “bottom”.

• Do not mix up the top and second ring.

• Install the top ring [A] so that the "R" mark [B] faces up.

• Install the second ring [C] so that the "RN" mark [D] faces

up.

 

 

NOTE

○If a new piston is used, use new piston ring.

• Install the piston with its marking hollow facing forward.

• Fit a new piston pin snap ring into the side of the piston

so that the ring opening [A] does not coincide with the slit

[B] of the piston pin hole.

○Apply molybdenum disulfide oil solution to the piston pins

and piston journals.

○When installing the piston pin snap ring, compress it only

CAUTION

Do not reuse snap rings, as removal weakens and deforms them. They could fall out and score the cylinder wall.

enough to install it and no more.

• Install the cylinder (see Cylinder Installation).

Cylinder Wear

• Since there is a difference in cylinder wear in different di- rections, take a side-to-side and a front-to-back measure-

ment at each of the two locations (total of four measure- ments) shown in the figure.

If any of the cylinder inside diameter measurements ex- ceeds the service limit, replace the cylinder.

10 mm (0.39 in.) [A]

60 mm (2.36 in.) [B]

Cylinder Inside Diameter

Standard: 82.994 ~ 83.006 mm (3.2675 ~ 3.2679 in.)