Ajustement de valve

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VALVE CLEARANCE
Inspection/Adjustment
Valve clearance is adjusted by a shim (Figure 62) in the recess at the top of each valve assembly (Figure 63). The shim and valve assembly are covered by a valve litter (Figure 64), often called a bucket. Each valve lifter is aligned below one of the camshaft lobes (Figure 65), which opens and closes the valve.
If the valve clearance is incorrcct. the camshafts and valve lifters must be removed so the shim size can be changed to bring each valve within specification. When removing valve lifters and shims. always record the clearance and shim size for each valve location. Keep each shim and valve lifter set identified by their cylinder head locations.
Shims are available in increments of 0.05 mm
(0.002 in.). Shim thickness ranges from 2.3 mm (a number 230 shim) to 3.5 mm (a number 350 shim). The number on the shim surface is the original thickness of the shim. For example, if the removed shim is marked 285, the shim is 2.85 mm thick.
When removing and installing shims. measure the shims with a caliper (Figure 66) to verify their actual thicknesses.
Commonly, when valve clearance is near the smallest acceptable clearance, the clearance is increased. even though the valve is technically within specification. Valves more often lose clearance than gain clearance between inspections, and therefore are adjusted toward the larger clearance specification. A small, marginally-acceptable clearance may be out of specification by the next inspection interval. However. do not increase clearance beyond the largest specification.
• 65 LUBRICATION, MAINTENANCE AND TUNE-UP
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IN
Check the valve clearance at the specified interval (Table I or Table 2) and when the engine is at ambient temperature.
I. Support the motorcycle so it is stable and secure.
2. Remove the cylinder head cover and set the engine at TDC as described in Chapter Four.
3. For each valve:
a. Use a flat feeler gauge to detennine the clearance between the valve lifter and cam lobe (Figure 67). Clearance is correct if slight resistance is felt when the gauge is inserted and withdrawn.
b. Record the measurement and valve location. This information is necessary to determine the correct size shim to install if out of specification.
4. If adjustment is required, refer to Chapter Four for camshaft and cam chain tensioner removal. Remove the camshaft from only the valve(s) that requires adjustment.
5. For each valve that requires adjustment, remove each valve lifter and shim set as follows:

1. Use a magnetic tool and raise the lifter straight up (Figure 64).
2. Lift out the valve shim resting on top of the valve stem.
3. Inspect each set of parts as they are removed. Both parts should be smooth on all surfaces. Light polishing on the shim, where it contacts the valve stem. is normal.
4. Clean and inspect the shim seat at the top of the valve assembly (Figure 63).
5. Mark the parts with their location in the cylinder head (Figure 6.

6. Detennine the shim size to install as follows:

1. Find the difference between the specified clearance and the existing clearance. This difference is the amount that must be added (loose val ve) or subtracted (tight valve) from the value of the shim removed in Step 5.
2. For example: If the existing clearance for an exhaust valve is 0.18 mm, and the specified clearance is 0.20-0.30 mm, the difference is 0.02-0.12 mm. In this example. the replacement shim should be this much smaller than the removed shim. If the removed shim is

2.85 mm thick (a number 285 shim), the replacement shim should be 2.75 mm thick (a number 275 shim). This would increase valve clearance to 0.28 111m (0.10 mm + 0.18 mm), which is within the specification.
7. Lubricate the replacement shim with engine oil, and then install the shim into the seat (Figure 63). Place the shim number facing up so it does not get worn away by the valve stem.
8. Lubricate the valve lifter with engine oil and install it over the shim and valve assembly (Figure 64).
9. Repeat the procedure for the remaining valves that are out of specification.
10. Install the eamshaft(s) and cam chain tensioner as described in Chapter Four.
II. Check valve clearance as follows:

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Valve clearance
Intake
0.10-0.20 (0.004-0.00
Exhaust
0.20-0.30 (0.008-0.012)

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