Cylinder head cover

Place head cover on a surface plate. There should be no warpage. Correct by re-surfacing as follows:

Place #400 or #600 grit wet sandpaper on surface plate and re-surface head cover using a figure-eight sanding pattern. Rotate head cover several times to avoid removing too much material from one side.

Cylinder head

1.    Using a rounded scraper, remove carbon deposits from combustion chamber. Take care to avoid damaging spark plug threads and valve seats. Do not use a sharp instrument. Avoid scratching the aluminum.

2.    Check the cylinder head warpage with a straight edge as shown.

The warpage should not exceed the specified limit, if necessary resurface. If the warpage exceeds allowable limit, the cylinder head should be replaced with a new one.

Cylinder head warpage: less than 0.05 mm (0.002 in)

Allowable limit: 0.25 mm (0.010 in)

1. Camshaft

a.   The cam lobe metal surface may have a blue discoloration due to excessive friction. The metal surface could also start to flake off or become pitted.

b.   If any of the above wear conditions are readily visible, the camshaft should be replaced.

c.   Even though the cam lobe surface appears to be in satisfactory condition, the lobes should be measured with a micrometer. Cam lobe wear can occur without scarring the surface. If this wear exceeds a pre-determined amount, valve timing and lift are affected. Replace the camshaft if wear exceeds the limits.

d. Install the camshaft on the cylinder head. Place a strip of Plastigage between camshaft and camshaft cap as illustrated (lengthwise along camshaft). Tighten the nuts with specified torque. Remove the camshaft cap and determine the clearance by measuring the width of the flattened Plastigage.

1. Plastigage

NOTE:
Do not turn camshaft when measuring clearance with Plastigage.

Camshaft-to-cap clearance:

Standard: 0.020 ~ 0.054 mm (0.0008-0.0021 in)

Maximum: 0.160 mm (0.006 in)

If the camshaft-to-cap clearance exceeds specification, measure camshaft bearing surface diameter.

Bearing surface diameter:

Standard: 24.967 ~ 24.980 mm (0.9830- 0.9835 in)

1)   If camshaft diameter is less than specification, causing excessive clearance, replace camshaft.

2)   If camshaft is within specification and camshaft-to-cap clearance is excessive, replace cylinder head.

2.    Cam chain

Except in cases of oil starvation, the cam chain wears very little. If the cam chain has stretched excessively and it is difficult to keep the proper cam chain tension, the chain should be replaced.

3.    Cam sprockets

Check cam sprockets for obvious wear.

4. Cam chain dampers and tensioner

Inspect the top cam chain damper (stopper guide) and two (2) vertical (slipper-type) dampers for excessive wear. Any that shows excessive wear should be replaced. Worn dampers may indicate an improperly adjusted or worn-out cam chain.

F. Cylinder

1.    Inspect the cylinder walls for scratches. If vertical scratches are evident, the cylinder wall should be rebored or the cylinder should be replaced.

2.    Measure cylinder wall wear as shown. If wear is excessive, compression pressure will decrease. Rebore the cylinder wall and replace the piston and piston rings. Cylinder wear should be measured at three depths with a cylinder bore gauge. (See illustration.)

Cap nut tightening torque: 1.0nvkg(7.2ft-ib)

	Standard	Wear Limit
Cylinder bore	57.00 mm (2.244 in)	57.10 mm (2.248 in)
Cylinder taper	-	0.05 mm (0.002 in)
Cylinder out-of-round		0.01 mm (0.0004 in)

If the cylinder wall is worn more than the wear limit, it should be rebored.

Valve, valve guide, and valve seat

1. Check the valve face and the stem end for wear. If the valve face and/or the stem end are pitted or worn, regrind the valve with a valve refacer. Replace the valve if any dimension exceeds the specifications in the illustration.

Intake/Exhaust valve

Minimum thickness (Service limit) 0.7 mm (0.028

Minimum length (Service limit) 4.0 mm (0.157 in)

2. Valve stem wear must be measured and then combined with valve guide measurements to guide clearance. This clearance must be within tolerances. If it exceeds the maximum limit, then replace either or both valve and guide, as necessary.

	Valve Stem Clearance	Maximum
Intake	0.010 ~ 0.037 mm (0.004 -0.0015 in)	0.10 mm (0.004 in}
Exhaust	0.025 ~ 0.052 mm (0.0010-0.0020 in)	0.12 mm (0.005 in)

3.    Valve stem end

Inspect the end of the valve stem. If the end appears to be "mushroomed" or has a larger diameter than the rest of the stem, the valve, valve guide, and oil seal should be replaced.

4.    Turn valve on "V" blocks and measure the amount of stem runout with a dial guage. If it exceeds the maximum limit, replace the valve.

Maximum valve stem runout: 0.03 mm (0.0012 in)

5. Valve guide and valve oil seal replacement If oil leaks into the cylinder through a valve due to a worn valve guide, or if a valve is replaced, the valve guide should also be replaced.

NOTE:
The valve oil seal should be replaced whenever a valve is removed or replaced.

a. Measure valve guide inside diameter with a small bore gauge. If it exceeds the limit, replace with an oversize valve guide.

Guide diameter (I.D.):  Limit: 6.10 mm (0.240 in!

b.  To ease guide removal and reinstallation, and to maintain the correct interference fit, heat the head to 100°C (212°F). Use an oven to avoid any possibility of head warpage due to uneven heating.

c.   Use the appropriate shouldered punch (special tool) to drive the old guide out and drive the new guide in,

NOTE:
When a valve guide is replaced, the O-ring should also be replaced.

1. Valve guide installer

d. After installing the valve guide, use the 6 mm reamer (special tool) to obtain the proper valve guide to valve stem clearance.

e. After installing the valve guide in the cylinder head, the valve seat must be recut. The valve should be lapped to the new seat.

6. Grinding the Valve Seat

a. The valve seat is subject to severe wear. Whenever the valve is replaced or the

valve face is re-surfaced (see caution) The valve seat should be re-surfaced at a 45° angle. If a new vlave guide has been installed the valve seat must be recut to guarantee complete sealing between the valve face and seat.

CAUTION:
If the valve seat is obviously pitted or worn, it should be cleaned with a valve seat cutter. Use the 45° cutter, and when twisting the cutter, keep an even downward pressure to prevent chatter marks.

If cutting section "A" of the valve seat, use 30° cutter. If cutting section "B", use the 45° cutter. If cutting section "C" use 60° cutter. b. Measure valve seat width. Apply mechanic's bluing dye (such as Dykem) to the valve face and valve seat, apply a very small amount of fine grinding compound around the surface of the valve face insert the valve into position, and spin the valve quickly back and forth. Lift the valve, clean off all grinding compound, and check valve seat width. The valve seat and valve face will have removed bluing wherever they contacted each other. Measure the seat width with vernier calipers. It should measure approximately 1.1 mm (0.0433 in). Also, the seat should be uniform in contact area. If valve seat width varies, or if pits still exist, further cutting will be necessary. Remove just enough material to achieve a satisfactory seat.

 

	Standard Width	Wear Limit
Seat width	1.0* 0.1 mm (0.0394 ±0.0039 in)	2.0 mm (0.080 in)

1. Valve guide remover

a. Seat width

c. If the valve seat is uniform around the perimeter of the valve face, but is too wide or not centered on the valve face, it must be altered. Use either the 30°, 45° or 60° cutters to correct the improper seat location in the manner described

1) If the valve face shows that the valve seat is centered on the valve face, but too wide, then lightly use both the 30° and the 60° cutters to reduce the seat width to 1.1 mm (0.0433 in).

1. Valve seat cutter

2)   If the seat shows to be in the middle of the valve face, but too narrow, use the 45° cutter until the width equals 1.1 mm (0.0433 in).

3)   If the seat istoo narrow and right up near the valve margin, then first use the 30° cutter and then the 45° cutter to get the correct seat width.

4)   If the seat is too narrow and down near the bottom edge of the valve face, then first use the 60° cutter and then the 45° cutter.

7. Lapping the valve/valve seat assembly

a.   The valve/valve seat assembly should be lapped if neither the seat nor the valve face are severely worn.

b.  Apply a small amount of coarse lapping compound to valve face. Insert the valve into the head. Rotate the valve until the valve and valve seat are evenly polished. Clean off the coarse compound, then follow the same procedure with fine compound.

Continue lapping until the valve face shows a complete and smooth surface all the way around. Clean off the compound material. Apply bluing dye to the valve face and seat and rotate the valve face for full seat contact which is indicated by a grey surface all around the valve face where the bluing has been rubbed awav.

Valve leakage check

After all work has been performed on the valve and valve seat, and all head parts have been assembled, check for proper valve/valve seat sealing by pouring solvent into each of the intake ports, then the exhaust ports. There should be no leakage past the seat. If fluid leaks, disassemble and continue to lap with fine lapping compound. Clean all parts thoroughly, reassemble and check again with solvent. Repeat this procedure as often as necessary to obtain a satisfactory seal.

1. Checking the valve springs

a.   This engine uses two springs of different sizes to prevent valve float or surging. The valve spring specifications show the basic value characteristics.

b.   Even though the spring is constructed of durable spring steel, it gradually loses some of it's tension. This is evidenced by a gradual shortening of free length. Use a vernier caliper to measure spring free length. If the free length of any spring has decreased more than 2 mm (0.080 in) from its specification replace it.

c. Another symptom of a fatigued spring is insufficient spring pressure when compressed. This can be checked using a valve spring compression rate gauge. Test each spring individually. Place it in the gauge and compress the spring first to the specified compressed length with the valve closed (all spring specifications can be found in the previous section, Valve Spring), then to the length with the valve open. Note the poundage indicated on the scale at each setting. Use this procedure with the outer springs, then the inner springs.

NOTE:
All valve springs must be installed with larger pitch upward as shown.

Valve Spring Specifications
	OUTER	INNER
Free length	37.2 mm 0.465 in)	35.5 mm (1.398 in)
Installed length (valve closed)	32.0 mm (1.260 in)	30.5 mm (1.201 in)
Installed pressure	18.5 kg (40.8 lb)	9.3 kg (20.5 lb)
Allowable tilt from vertical	2.6°	4-

2. Valve lifter

a. Check each valve lifter for scratches or other damage. If the lifter is damaged in any way, the cylinder head surface in which it rides is probably also damaged. If the damage is severe, it may be necessary to replace both the lifter and the cylinder head.

NOTE:
For proper valve lifter-to-head clearance, always install lifters on their original valves.

Piston

a. Measure the outside diameter of the piston at the piston skirt. Measurement should be made at a point 7.5 mm (0.3 in) above the bottom edge of the piston. Place the micrometer at right angles to the piston pin.

Standard		57.00 mm (2.244 in)
Oversize 1		57.25 mm (2.254 in)
Oversize 2		57.50 mm (2.264 in)
Oversize 3		57.75 mm (2.274 in)
Oversize 4		58.00 mm (2.284 in)

a. 7.0 mm (0.28 in)

b. Determine piston clearance as follows:

Minimum bore measurement - Maximum piston measurement = Piston clearance

EXAMPLE:

57.00 mm (2.2440 in) - 56.96 mm (2.2424 in) = 0.04 mm (0.0016 in)

Piston clearance

Piston clearance:
Standard:	0.025-0.045 mm
	(0.0010 - 0.0018 in)
Service limit:	0.1 mm (0.0039 in)

c. Piston ring/ring groove fit must have correct clearance. If the piston and ring have already been used, the ring must be removed and the ring groove cleaned of carbon. The ring should then be reinstalled. Use a feeler gauge to measure the gap between the ring and the land.

Side clearance	Top	0.03-0.07 mm (0.0012-0.0028 in)
	2nd	0.02 -0.06 mm (0.0008 -0.0024 in)

1.  Feeler gauge

Piston ring

a. The oversize top and middle ring sizes are stamped on top of the ring.

Oversize 1	0.25 mm (0.0098 in)
Oversize 2	0.50 mm (0.0197 in)
Oversize 3	0.75 mm (0.0295 in)
Oversize 4	1.00 mm (0.0394 in)

b. The expander spacer of the bottom ring (oil control ring) is color-coded to identify sizes.

The color mark is painted on the expander spacer.

Size	Color
Oversize 1	Brown
Oversize 2	Blue
Oversize 3	Black
Oversize 4	Yellow

c. Push the ring into the bore and check end gap clearance with a feeler gauge.

NOTE:
The end gap on the expander spacer of the oil control ring is unmeasurable. If the oil control ring rails show excessive gap, all three components should be replaced.

	Standard	Limit
Top/2nd ring	0.15~0.35 mm (0.006-0.014 in)	1.0 mm (0.039 in}
Oil control (Rails)	0.3 -0.9 mm (0.012^0.035 in)	1.5 mm (0.059 in)

Piston pin

1.    Apply a light film of oil to pin. Install in connecting rod small end. Check for play. There should be no noticeable vertical play. If play exists, check connecting rod small end for wear. Replace pin and connecting rod as required.

2.    The piston pin should have no noticeable free play in piston. If the piston pin is loose, replace the pin and/or the piston.

1. Crankshaft run-out

Support the crankshaft at both ends on V-blocks. Measure the amount of crankshaft run-out on the main bearing journals with a dial gauge while rotating crankshaft.

Run-out limit: 0.03 mm (0.0012 in)

If run-out exceeds limit, replace crankshaft.

2.    Inspection of bearings

Check the bearings. If the inner or outer surface is burned,flaked, rough, scratched or worn, the bearings should be replaced.

3.    Measuring main bearing oil clearance

a.   Clean all crankshaft and crankcase journal surfaces.

b.  Place upper crankcase half upside-down on a bench. Install bearing inserts into top crankcase.

c.   Install crankshaft into upper crankcase.

d.  Place Plastigage on crankshaft journal surface to be inspected.

NOTE:
Do not move crankshaft until clearance check has been completed.

e.   Install bearings into bottom crankcase. Carefully, place lower crankcase onto upper crankcase.

f.    Install crankcase holding bolts 1 through 10. Tighten to full torque in torque sequence cast on crankcase.

Crankcase torque (8 mm bolt): 2.4 m-kg (17.5 ft-lb)

g. Remove bolts in reverse assembly order (10, 9, 8...etc.)

h. Carefully remove lower crankcase. Measure width of Plastigage on crankshaft journals to determine clearance.

Main bearing oil clearance: 0.040- 0.064 mm (0.0016- 0.0025 in)

1. Plasligage

4. Crankshaft main bearing and connecting rod bearing selection

a. Numbers used to indicate crankshaft journal sizes are stamped on the L.H. crankweb. The first five (5) are main bearing journal numbers, starting with the left journal. The four (4) rod bearing journal numbers follow in the same sequence.

The upper crankcase half is numbered 4, 5, or 6 as shown.

b. The connecting rods are numbered 4 or 5. The numbers for rods are stamped with ink on the rod itself.

1. Connecting rod size number

c. The proper bearing selection is made by subtracting the crankshaft journal number from the crankcase or rod size number. Use the color code to choose the proper bearing.

EXAMPLE:

Rod No. (Minus) Journal No. = Bearing No.

5-2 = 3 No. 3 bearing is Brown. Use Brown bearing inserts.

BEARING COLOR CODE
No. 1	Blue
No. 2	Black
No. 3	Brown
No. 4	Green
"No. 5	Yellow

For crankshaft main bearing only.

d. When assembling, apply a liberal coat of motor oil to all bearing surfaces.

NOTE:
When applying final torque to the rod caps, observe the following procedures:

e. Apply molybdenum disulfide grease to connecting rod bolt threads. Apply torque evenly to both ends of the cap. While tightening, if a torque of 2.0 m-kg (14.5 ft-lb) or more is reached, DO NOT STOP tightening until final torque is reached. If tightening is interrupted between 2.0 m-kg and 2.5 m-kg, loosen the nut to less than 2.0 m-kg and start again. Tighten to full torque specification without pausing.

Oil pump

1. Check the clearance between housing and outer rotor.

Standard clearance:

0.09 ~ 0.15 mm (0.0035 ~ 0.0059 in)

2. Check the clearance between outer rotor and inner rotor.

Standard clearance: 0.03 ~ 0.09 mm (0.0012 ~ 0.0035 in)

3. Check the plunger for scrathces and wear.

Clutch

1. Clutch housing

a. Check the dogs on the clutch housing.

Look for cracks and signs of galling on

edges. If damage is moderate, deburr.

If severe, replace the clutch housing.

NOTE:
Galling on the friction plate dogs of the clutch housing will cause erratic clutch operation.

b. Check the clutch housing bearing for

damage. If damaged replace bearing. 2. Clutch boss

a.   The clutch boss contains a built-in damper beneath the first clutch plate (clutch plate 2). It is not normally necessary to remove the circlip and disassemble the built-in damper unless there is serious clutch chattering.

b.  Check splines on clutch boss for galling. If damage is slight to moderate, deburr; if it is severe, replace clutch boss.

NOTE:
Galling on clutch plate splines will cause erratic operation.

3. Friction and clutch plates

Check clutch steel plates and friction plates for heat damage. Measure friction plate thickness at 3 or 4 points. Measure clutch plates for warpage with a dial gauge and stand. Replace clutch plate or friction plates as a set if any is faulty or beyond wear limits.

	Standard Wear limit
Friction plate thickness	3.0 mm (0.12 in)	2.8 mm (0.11 in)
Clutch plate warp limit	-	0.15 mm (0.006 in)

1. Feeler gauge

4. Clutch actuating mechanism

1. Plate washer 2. Thrust bearing 3. Pull rod

a.   Check the pull rod rack gear teeth for wear and damage, replace if damaged.

b.  Check the pull rod thrust bearing for damage, replace if damaged.

c.   Check the clutch lever shaft pinion gear teeth for damage, replace if damaged.

5. Clutch springs

Measure the clutch spring free length. Replace the springs as a set if any is less than minimum free length.

Clutch spring minimum length: 40.2 mm (1.583 in)

Inspect each shift fork signs of galling on gear contact surfaces. Check for bending. Make sure each fork slides freely on its guide bar.

2.    Roll the guide bar across a surface place. If the bar is bent, replace.

3.    Check the shift cam grooves for signs of wear or damage. If any profile has excessive wear and/or damage, replace cam.

4.    Check the cam followers on each shift fork for wear. Check the ends that ride in the grooves in the shift cam. If they are worn or damaged, replace the shift forks.

5.    Check shift cam dowel pins and side plate for looseness, damage or wear. Replace as required.

6.    Check the shift cam stopper plate and circlip and stopper for wear. Replace as required.

7.    Check the transmission shafts using a centering device and dial gauge. If any shaft is bent beyond specified limit, replace shaft.

Maximum run-out: 0.08 mm (0.0031 in!

8.    Carefully inspect each gear. Look for signs of obvious heat damage (blue discoloration). Check the gear teeth for signs of pitting, galling or other extreme wear. Replace as required.

9.    Check to see that each gear moves freely on its shaft.

10.    Check to see that all washers and clips are properly installed and undamaged, Replace bent or loose clips and bent washers.

11.    Check to see that each gear properly engages its counterpart on the shaft. Check the mating dogs for rounded edges, cracks, or missing portions. Replace as required.

M. Starter drivers

Electric starter clutch and gears

a. Check the surface of the idle gear for pitting or other damage. If severe, replace the gear.

b. Check the spring caps and the springs for deformation or damage. If severe, replace as necessary.

c. Check the starter clutch bolts (alien screw) for looseness. If loose, remove the bolts and replace with new bolts.

Apply a thread locking compound such as "LOCTITE" to threads and tighten to specified torque. Stake over the end of the bolts.

Starter clutch bolt torque: 2.5m-kg (18.0 ft-lb)

d.  Check the "HY-VO" chain for damage and wear, replace if damaged.

e.   Check the "HY-VO" chain guide for damage, replace if damaged.

Crankcase and strainer cover

1.    Check crankcase for cracks or other damage.

2.    Clean all oil passages and blow out with compressed air.

3.    Strainer cover: Apply a thread locking compound such as "LOCTITE" to strainer cover bolts during reassembly.

Bearing and oil seals

1. After cleaning and lubricating bearings, rorate inner race with a finger. If rough spots are felt, replace the bearing.

NOTE:
Bearings are most easily removed or installed if the housings are first heated to approximately 95° - 125°C (200°- 250°F). Bring the case up to proper temperature slowly. Use an oven to avoid distortion.

2. Check oil seal lips for damage and wear. Replace as required.