201j - Cylinder Head Fundamentals Flashcards
What method of construction is used to manufacture cylinder heads?
Casting
cast iron allow or aluminum
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Four-valve cylinder heads off what advantages over two-valve cylinder heads?
- Volumetric efficiency
- Turbulence
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On a two stroke engine, how many exhaust valves would there be with a two-valve cylinder head design?
Two exhaust valves
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What is a benefit of having more smaller valves instead of less larger valves?
Having more smaller valves offers greater combined valve head area and less valve inertia.
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What are injector tubes/cups usually made of? (3)
- Copper
- Stainless steel
- Brass
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There must be a seal between the injector tube and the cylinder head to prevent: (2)
- Coolant from leaking past tube into combustion chamber
- Combustion gasses from leaking past tube into cooling system
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What component directs coolant flow to critical areas of the cylinder head?
Coolant directional nozzles
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What do coolant directional nozzles do?
Direct coolant flow to critical areas of the cylinder head such as exhaust valve seats.
Valves perform what two basic functions?
- Open and close the cylinder to allow airflow during intake and exhaust events
- Seal the cylinder during compression and power events
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What is the role of the valve lock groove?
Machined into the stem of the valve and mates with a lug on the valve locks. Valve locks and retainer keep the valve and spring together.
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What is the role of the valve fillet?
The smooth radius area between stem and face that provides strength and stress relief. The radius also enhances airflow past the valve.
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What is the role of the valve face?
Smooth machined surface that mates with the valve seat in the cylinder head to seal in combustion gasses and transfer heat.
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What is the role of the valve margin?
Material between the valve face and valve head. Supports the face and provides material for heat absorption.
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What are the different parts of a valve? (7)
Tip
Valve lock groove
Stem
Fillet
Valve face
Margin
Valve head
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Why is the exhaust valve typically made of better quality material than the intake valve?
Operates at higher temperatures and with corrosive gases.
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The lower end of certain valve stems are machined to a slightly smaller diameter. Why is this?
The machined step acts as a carbon scraper when it moves in and out of the valve guide. This helps keep the lower part of the valve guide clean and reduces carbon buildup.
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What percentage of cooling occurs through a solid valve stem between the valve face and valve seat?
75%
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What percentage of cooling occurs in a solid valve stem between the valve stem and valve guide?
25%
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A sodium cooled exhaust valve transfers approximately what percentage of its heat from the valve stem to valve guide?
50%
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Overall, sodium filled exhaust valves operate what percentage cooler than solid valve stems?
15%
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