How much should I pay for a valve clearance?
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11-25-2008, 09:04 PM
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11-25-2008, 09:34 PM
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RE: How much should I pay for a valve clearance?
allow me to wikipedia...
Valve clearance refers to the small gap between a valve lifter and a valve stem (or between a rocker arm and a valve stem) that ensures that the valve completely closes. On engines that require manual valve adjustment, excessive clearance will cause excessive noise from the valve train (“hammering”) during operation. Improper valve clearance reduces engine performance and increases wear and noise.
Most engines have the valve clearance set by grinding the end of the valve stem during engine assembly, overhead cams not needing subsequent adjustment. All engines with poppet-type valves make some sort of allowance for maintaining this "expansion joint", while less sophisticated engines use solid, "non-adjustable” components which are simply ground off at the contact points to provide the correct clearance (though the low efficiency of this design may not be practical when the cost of labor is very high). Another method is to provide some method of manually changing the clearance with adjustable screws or shims, the implementation of which depends on and varies widely with the design of the engine. Manual valve lash adjustment is used in almost all very high performance engines because the hydraulic adjusters used in "automatic" systems are often affected by the extreme valve train accelerations of ultra high-speed engines.
Most modern production engines use some form of automatic valve adjustment (usually hydraulic) to maintain a state known as "zero lash". In pushrod and some OHC engines this adjuster is incorporated into the tappet, lash adjuster or tip of the rocker. Many DOHC engines now employ tiny hydraulic lash adjusters in the top of the cam followers to maintain "zero lash". "Zero lash" is a desirable condition, since this allows for very quiet engine operation. Hydraulic lifters or lash adjusters also reduce required maintenance, reduce noise, help engines to perform at peak efficiency and minimize exhaust emissions by compensating for wear and expansion of various engine components. Earlier engines, mostly those with push rods and rocker arms, used adjustable tappets or hydraulic lifters to automatically compensate for valve train component and camshaft wear. Lack of valve clearance will prevent valve closure causing leakage and valve damage.
Valve clearance adjustment must be performed to manufacturer's specifications. It is normal that the exhaust valve will have a larger clearance. Adjustment is performed by either adjusting the rocker arm or placing shims between cam follower and valve stem. Most modern engines have hydraulic lifters and require only infrequent adjustment.[citation needed]
Valve clearance is measured with the valve closed, typically at top dead center between the compression and power strokes. The tappet will be resting on the heel of the cam lobe. A feeler gauge must pass through the clearance space. The feeler gauge should fit in and out with a slight drag. If the feeler gauge will not fit in, then the clearance is too small. If the blade of the feeler gauge fits in too loosely, the clearance is too large.
A too-wide valve clearance causes excessive wear of the camshaft and valve lifter contact areas, and noise. Should the clearance become wide enough, valve timing is significantly affected, resulting in poor performance.
A too-narrow valve clearance does not allow for heat expansion and results in the failure of the valve to fully close. The combustion chamber does not seal properly, resulting in poor compression, which reduces performance. The valve can also overheat and even melt. However heat expansion can have the opposite effect in overhead cam engines that use aluminum alloy cylinder heads. The coefficients of thermal expansion of aluminum alloys are approximately twice that of the steel used for the valve train and this expansion can increase the clearance.
cost? Between 200 and 500... depending on if they need adjusted. the valves are pretty easy to check... but not so easy to fix if they do need adjusted...
Valve clearance refers to the small gap between a valve lifter and a valve stem (or between a rocker arm and a valve stem) that ensures that the valve completely closes. On engines that require manual valve adjustment, excessive clearance will cause excessive noise from the valve train (“hammering”) during operation. Improper valve clearance reduces engine performance and increases wear and noise.
Most engines have the valve clearance set by grinding the end of the valve stem during engine assembly, overhead cams not needing subsequent adjustment. All engines with poppet-type valves make some sort of allowance for maintaining this "expansion joint", while less sophisticated engines use solid, "non-adjustable” components which are simply ground off at the contact points to provide the correct clearance (though the low efficiency of this design may not be practical when the cost of labor is very high). Another method is to provide some method of manually changing the clearance with adjustable screws or shims, the implementation of which depends on and varies widely with the design of the engine. Manual valve lash adjustment is used in almost all very high performance engines because the hydraulic adjusters used in "automatic" systems are often affected by the extreme valve train accelerations of ultra high-speed engines.
Most modern production engines use some form of automatic valve adjustment (usually hydraulic) to maintain a state known as "zero lash". In pushrod and some OHC engines this adjuster is incorporated into the tappet, lash adjuster or tip of the rocker. Many DOHC engines now employ tiny hydraulic lash adjusters in the top of the cam followers to maintain "zero lash". "Zero lash" is a desirable condition, since this allows for very quiet engine operation. Hydraulic lifters or lash adjusters also reduce required maintenance, reduce noise, help engines to perform at peak efficiency and minimize exhaust emissions by compensating for wear and expansion of various engine components. Earlier engines, mostly those with push rods and rocker arms, used adjustable tappets or hydraulic lifters to automatically compensate for valve train component and camshaft wear. Lack of valve clearance will prevent valve closure causing leakage and valve damage.
Valve clearance adjustment must be performed to manufacturer's specifications. It is normal that the exhaust valve will have a larger clearance. Adjustment is performed by either adjusting the rocker arm or placing shims between cam follower and valve stem. Most modern engines have hydraulic lifters and require only infrequent adjustment.[citation needed]
Valve clearance is measured with the valve closed, typically at top dead center between the compression and power strokes. The tappet will be resting on the heel of the cam lobe. A feeler gauge must pass through the clearance space. The feeler gauge should fit in and out with a slight drag. If the feeler gauge will not fit in, then the clearance is too small. If the blade of the feeler gauge fits in too loosely, the clearance is too large.
A too-wide valve clearance causes excessive wear of the camshaft and valve lifter contact areas, and noise. Should the clearance become wide enough, valve timing is significantly affected, resulting in poor performance.
A too-narrow valve clearance does not allow for heat expansion and results in the failure of the valve to fully close. The combustion chamber does not seal properly, resulting in poor compression, which reduces performance. The valve can also overheat and even melt. However heat expansion can have the opposite effect in overhead cam engines that use aluminum alloy cylinder heads. The coefficients of thermal expansion of aluminum alloys are approximately twice that of the steel used for the valve train and this expansion can increase the clearance.
cost? Between 200 and 500... depending on if they need adjusted. the valves are pretty easy to check... but not so easy to fix if they do need adjusted...
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11-26-2008, 01:05 AM
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11-26-2008, 01:01 PM
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RE: How much should I pay for a valve clearance?
on an F4i and most other contemporary sport bikes they use shim/bucket setup
the tight clearance between the head and frame requires that the motor be removed if the valve clearance is out of specs
a service manual will give you all the details you need to check your clearance if you feel up to it
the tight clearance between the head and frame requires that the motor be removed if the valve clearance is out of specs
a service manual will give you all the details you need to check your clearance if you feel up to it
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