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AGEN 100 Lab #3 Mr. Cross Valve Adjustment Lab
A valve may be defined as a device used for closing a passage. The operation of an internal combustion engine necessitates nec essitates the admission, trapping and exhausting of the fuel air mixture, all of which are accomplished by valve. Their proper operation is essential to both good engine performance and fuel economy. The type of valve most commonly found in present day internal combustion engines is the poppet valve. The most common valve arrangement is the overhead ori head. Valve arrangement refers to the location and grouping of valves to make the most efficient use of intake and exhaust manifold ports. Most engines are arranged so that two valves utilize one port, especially especially in gasoline engines. Diesels, due to their their inherent nature, may have one port per valve and may increase volumetric efficiency. efficiency. On gasoline engines intake manifolds are made as short as possible to help provide a uniform distribution of the air fuel mixture to all cylinders. Intake and exhaust valves can be identified by noting which manifold leads to an individual port. Valve arrangements most commonly used are the “L” head or flathead, and the “I” head or valve in head. The L-head arrangement has the valves located in in the engine block. The I-Head has valves located in in the cylinder head and is properly properly called an overhead valve engine or valve in head engine. L-Head engines have a simple valve mechanism. mechanism. The camshaft actuates the valve through a valve lifter or cam follower which comes in direct contact with the valve stem. Adjustment on this type valve arrangement is usually by an adjusting screw and lock nut found on the lifter or cam follower. In some cases no adjustment adjustment was provided, just initial fit by grinding the valve stem to lifter lifter clearance. This type lifter lifter was termed nonadjustable and has since been out of production for at least 20 years on larger engines. The adjustable type lifer may require special tools tools to facilitate adjustment. adjustment. In the I-Head engine all of the combustion combustion space is directly over the piston. The camshaft actuates the valves through a valve lifter, lifter, which in turn operates a push rod. The pushrod operates a rocker arm that pivots pivots on the rocker arm shaft. shaft. The rocker arm comes in contact with the valve stem to produce valve action. It is evident that the I-Head with its complex mechanism will need more frequent adjustment. Adjustment of rocker arm to valve stem clearance or valve lash is set by an adjusting screw found on the rocker arm assembly which is turned to provide proper clearance between the rocker arm and valve stem. It should be noted that most most automotive engines have self-adjusting valve lifters to eliminate the ne ed for adjustment. However, few if any of these are used on agricultural engines. Adjusting the clearance between the valve stem and valve lifter or rocker arm is essential to allow for the expansion due to heat that will tend to lengthen or expand the valve stem. When the engine reaches normal operating temperature, temperature, there must be enough clearance between the lifter and stem to allow the valve spring to close the valve face flush against the valve seat. seat. In insufficient clearance is maintained the escaping exhaust gasses will burn the the face of the exhaust valve. Improper clearance on the intake valve will result in late valve timing and excessive noise and wear to the valve train.
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AGEN 100 Lab #3 Mr. Cross Questions
1. List and explain the steps for adjusting clearance.
2. In what position must the engine be in to adjust the valves?
3. Which valve requires greater clearance? Why?
4. List the clearances and the type engine:
5. Prepare a drawing showing the valve order and label each cylinder.
6. Are valves adjusted hot or cold for your engine?
7. What are the two most common valve arrangements?
8. Why is valve timing important?
9. How is the valve train timed with the action of the pistons?
10. At what speed compared to the crankshaft speed does the valve train run? Why?
11. How is speed reduction obtained in the valve train of the engine you worked on?
