Đang tải... (xem toàn văn)
Tài liệu học tập cơ bản khái quát về động cơ và các bộ phận trên ô tô phiên bản tiếng anh. Tài liệu này nhằm giúp chúng ta tiếp cận được cấu tạo chức năng của các bộ phận của xe. Với tài liệu này giúp các bạn sinh viên ngành cơ khí ô tô tiếp cận được những kiến thức cơ bản về ô tô và đồng thời nâng cao kiến thức tiếng anh. Bộ tài liệu này được soạn thảo bởi trường đào tạo và huấn luyện nghề ở Canada.
Chapter 12 Upper End Theory and Service Cylinder Heads • Made of cast iron or aluminum • Contains valves, valve seats, valve guides, springs, rocker arm supports, and the upper portion of the combustion chamber • Contains coolant and oil return passages • Head design is one of the most influential factors in overall engine performance Cylinder Heads (cont’d) • Intake and exhaust ports are cast into the head • Most heads are aluminum to reduce weight • Heads can have crossflow or Siamese port Wedge Combustion Chamber Hemispherical Combustion Chamber Pentroof Combustion Chamber Intake and Exhaust Valves • Commonly called poppet valves • Allow air to flow into and exhaust out of the combustion chamber • Seal the upper portion of combustion chamber • Intake valves are larger than exhaust valves Valve Terminology Valve Seats • May be cast into or inserted into head • Seals the valve and transfers heat Valve Guides • Support the valve and allow only up and down motion • Close clearance to valve stem • Keeps valve aligned with valve seat • Can be cast into or insert into the head Valves Seats • Inspect for damage, burning, cracks, and deterioration • Check for loose seats • Inspect for sunken valve seats • Seats should be replaced if the valve was broken or bent Retainers and Keepers • Worn retainers will allow the spring to move away from the valve centerline • Uneven wear on the stem tip indicators rotators not working properly • A - is freestanding height • B - is closed valve spring height • C - is open valve spring height Valve Face • Valve face angles and dimensions must be kept within specifications Valve Stem • Grinding the face sets the valve lower into the port – extending the stem height Valve Stem (cont’d) • If stem height is excessive, the valve stem tip may be ground • Chamfer valve tip after grinding • Valve and/or seat may need to be replaced to correct incorrect stem height Valve Guide Clearance • Measure the guide diameter and stem diameter Valve Guide Problems • Inadequate Lubrication – Is caused by oil starvation in the upper valve train • Valve Geometry Problems – Lead to increased guide clearance, poor valve seating, and premature wear • Wrong Stem to Guide Clearance – Can cause increased oil consumption Valve Guide Reconditioning Measuring Seat Width Valve Stem Seals • Control the amount of oil between the stem and guide Assembling the Cylinder Head • Installed stem height and installed spring height must be checked • Stem height affected by valve and seat • Spring height may be adjusted using shims ... valves, valve seats, valve guides, springs, rocker arm supports, and the upper portion of the combustion chamber • Contains coolant and oil return passages • Head design is one of the most influential... Pentroof Combustion Chamber Intake and Exhaust Valves • Commonly called poppet valves • Allow air to flow into and exhaust out of the combustion chamber • Seal the upper portion of combustion chamber... Seats • May be cast into or inserted into head • Seals the valve and transfers heat Valve Guides • Support the valve and allow only up and down motion • Close clearance to valve stem • Keeps valve