CH011 Cylinder Heads, Camshafts, and Valve Trains

1、Copyright 2007 by Nelson, a division of Thomson Canada Limited. 11-1Chapter 11 Prepared by Martin Restoule Algonquin College Copyright 2007 by Nelson, a division of Thomson Canada Limited. 11-2Chapter 11 Describe the purpose of an engines cylinder head, valves, and related valve parts. Describe the

2、types of combustion chamber shapes found on modern engines. continued Copyright 2007 by Nelson, a division of Thomson Canada Limited. 11-3Chapter 11 Explain the procedures involved in reconditioning cylinder heads, valve guides, valve seats, and valve faces. Explain the steps in cylinder head and va

3、lve reassembly. Copyright 2007 by Nelson, a division of Thomson Canada Limited. 11-4Chapter 11 Wedge chamber The spark plug is located at the wide part of the wedge. Hemispherical chamber The combustion chamber is shaped like a half circle. The spark plug is located in the centre of the combustion c

4、hamber. continued Copyright 2007 by Nelson, a division of Thomson Canada Limited. 11-5Chapter 11 Copyright 2007 by Nelson, a division of Thomson Canada Limited. 11-6Chapter 11 continued Copyright 2007 by Nelson, a division of Thomson Canada Limited. 11-7Chapter 11 Intake valves Exhaust valves Valve

5、guides Valve springs, retainers, keepers, and seals Valve rotators Copyright 2007 by Nelson, a division of Thomson Canada Limited. 11-8Chapter 11 Copyright 2007 by Nelson, a division of Thomson Canada Limited. 11-9Chapter 11 Copyright 2007 by Nelson, a division of Thomson Canada Limited. 11-10Chapte

6、r 11 Valve guides Integral or inserted bores in the cylinder head that support the valves in the head. Prevent oil from entering the combustion chamber during the intake stroke. Keep exhaust vapours from leaking into the crankcase area during the exhaust stroke. Keep the valve face in alignment with

7、 the valve seat. continued Copyright 2007 by Nelson, a division of Thomson Canada Limited. 11-11Chapter 11 Copyright 2007 by Nelson, a division of Thomson Canada Limited. 11-12Chapter 11 Inadequate lubrication Is caused by oil starvation in the upper valve train. Valve geometry problems Lead to incr

8、eased guide clearance, poor valve seating, and premature wear. Wrong stem to guide clearance Can cause increased oil consumption. Copyright 2007 by Nelson, a division of Thomson Canada Limited. 11-13Chapter 11 Valve springs hold the valve tight to the seat when closed and tight to the valve train wh

9、en the camshaft is pushing the valve open. Valve springs come in a variety of designs to reduce vibration caused by harmonics during operation. Copyright 2007 by Nelson, a division of Thomson Canada Limited. 11-14Chapter 11 Freestanding height test Spring squareness test Open/close spring pressure t

10、est Copyright 2007 by Nelson, a division of Thomson Canada Limited. 11-15Chapter 11 Retainers and keepers are designed to positively hold the valve spring in place with the valve while allowing the spring to be removed for valve and spring service. The valve spring tension against the retainer holds

11、 the keepers tightly in the valves keeper grooves. Copyright 2007 by Nelson, a division of Thomson Canada Limited. 11-16Chapter 11 Valve seals control the amount of oil that is present at the top of the valve guide. Valve seals can be a passive or positive design. Copyright 2007 by Nelson, a divisio

12、n of Thomson Canada Limited. 11-17Chapter 11 Valve rotators are used to rotate the valve to prevent the formation of carbon deposits on the valve face and from allowing the valve face from burning. A rotating valve will prevent the valve face from remaining in a constant hot location in the combusti

13、on chamber. Copyright 2007 by Nelson, a division of Thomson Canada Limited. 11-18Chapter 11 Copyright 2007 by Nelson, a division of Thomson Canada Limited. 11-19Chapter 11 Inspect the timing belt or chain sprockets for wear or damage. Inspect the rocker shaft assembly for wear. Check the straightnes

14、s of the pushrods. Check overhead cam follower components for damage and wear. Inspect retainers for cracks. Copyright 2007 by Nelson, a division of Thomson Canada Limited. 11-20Chapter 11 Replace valve rotators when valves are refaced. Check valve spring assemblies for cracks, breaks, or damage. Ca

15、refully inspect cylinder heads after cleaning. Always replace cam bearings when rebuilding. Check valves for evidence of burning. Copyright 2007 by Nelson, a division of Thomson Canada Limited. 11-21Chapter 11 Deck Resurfacing To make the sealing surface flat so the gasket seals properly. To raise t

16、he compression ratio. To square the deck to the main bores. Depending on the tools available and the cylinder head material the deck can be resurfaced by grinding, milling, belt surfacing, or broaching. continued Copyright 2007 by Nelson, a division of Thomson Canada Limited. 11-22Chapter 11 The cyl

17、inder head deck surface can easily be checked for warpage with a precision straight edge and feeler gauge along the head and diagonally. Check your measurements against the specifications. continued Copyright 2007 by Nelson, a division of Thomson Canada Limited. 11-23Chapter 11 Valve Resurfacing Whe

18、never the valves have been removed from the cylinder head, the valve face and valve seats should be resurfaced. Leakage between these surfaces reduces the engines compression and power and can lead to valve burning. continued Copyright 2007 by Nelson, a division of Thomson Canada Limited. 11-24Chapt

19、er 11 Valve Reconditioning To ensure proper seating of the valve, the seat area on the valve face and seat must be the correct width, at the correct location, and concentric with the guide. These are accomplished by renewing the surface of the valve face and seat. Valve grinding or refacing is done

20、by machining a fresh, smooth surface on the valve faces and stem tips. continued Copyright 2007 by Nelson, a division of Thomson Canada Limited. 11-25Chapter 11 Valve Resurfacing Valve faces suffer from burning, pitting, and wear caused by opening and closing millions of times during the life of an

21、engine. Valve stem tips wear because of friction from the rocker arms or actuators. Valve tips are machined after the valve face is refinished. Valves can be refaced on either grinding or cutting machines. continued Copyright 2007 by Nelson, a division of Thomson Canada Limited. 11-26Chapter 11 Perf

22、orming the valve grinding operation; Chuck the valve as close as possible to the valve head. Set the grinding angle according to the desired angle. Interference angles are normally 0.5 to 1 less than the seat. Copyright 2007 by Nelson, a division of Thomson Canada Limited. 11-27Chapter 11 Performing

23、 the valve grinding operation; Take light cuts using the full grinding wheel width. Make sure coolant is striking the valve face. Remove only enough metal to clean up the valve face. continued Copyright 2007 by Nelson, a division of Thomson Canada Limited. 11-28Chapter 11 Valve Guide Service If guid

24、e measurements show guide wear the guide bore must be restored through machining or guide replacement. Slightly worn guides can be restored through knurling the guides bore. This is a quick and inexpensive repair that virtually does not affect the guides centreline and allows for the use of the old

25、valve. continued Copyright 2007 by Nelson, a division of Thomson Canada Limited. 11-29Chapter 11 Reaming Reaming is used to repair worn guides by increasing the guide hole size to take an oversize valve stem or by restoring the guide to its original diameter after installing inserts or knurling. Whe

26、n reaming, limit the amount of metal removed per pass. Always reface the valve seat after the valve guide has been reamed. continued Copyright 2007 by Nelson, a division of Thomson Canada Limited. 11-30Chapter 11 Thin Wall Guide Liners Thin-wall guide liners offer a number of important advantages an

27、d are also popular with many production engine rebuilders, as well as smaller shops. It provides the benefits of a bronze guide surface. It can be used in either integral or replaceable guides. It is faster, easier, and cheaper than installing new guides in heads with replaceable or integral guides,

28、 and it maintains guide centring with respect to the seats. continued Copyright 2007 by Nelson, a division of Thomson Canada Limited. 11-31Chapter 11 Thin Wall Guide Liners These liners can be cut to almost any length and are designed for a press fit. A tight fit is essential for proper heat transfe

29、r to the head and to prevent the liner from working loose. continued Copyright 2007 by Nelson, a division of Thomson Canada Limited. 11-32Chapter 11 Replaceable Guides Replacing the entire valve guide is another repair option possible on cylinder heads with replaceable guides. Pressing out the old g

30、uides and installing new ones can be difficult with some aluminum heads because cracking the head or galling the guide hole is always a risk. The manufacturers specifications give the correct valve guide installed height continued Copyright 2007 by Nelson, a division of Thomson Canada Limited. 11-33

31、Chapter 11 Concentricity Occasionally, a new guide will not be concentric with the valve seat. Install a new seat to correct the problem and check the concentricity of the valve seat with a concentricity gauge. continued Copyright 2007 by Nelson, a division of Thomson Canada Limited. 11-34Chapter 11

32、 Valve Seat Reconditioning For proper seating of the valve, the valve seat must be the correct width, in the correct location on the valve face, and concentric with the guide. The ideal seat width for automotive engines is 1.59 mm for intake valves and 2.38 mm for exhaust valves. When an existing se

33、at is refinished to make it smooth and concentric, it also becomes wider. continued Copyright 2007 by Nelson, a division of Thomson Canada Limited. 11-35Chapter 11 Valve Seat Reconditioning Valve seats can be reconditioned or repaired by one of two methods, depending on the seat typemachining a coun

34、terbore to install an insert seat, or grinding, cutting, or machining an integral seat. continued Copyright 2007 by Nelson, a division of Thomson Canada Limited. 11-36Chapter 11 Valve Seat Reconditioning A properly reconditioned seat has 3 angles: top - 30/15; seat - 45/30; and throat - 60. Typicall

35、y, the 45 angle seat wedges tighter and is used more often. Using 3 angles maintains the correct seat width and sealing position and pressure on the valve face. continued Copyright 2007 by Nelson, a division of Thomson Canada Limited. 11-37Chapter 11 Valve Seat Reconditioning When grinding a valve s

36、eat, it is very important to select and use the correct size pilot and grind stone. The stone must be properly dressed and cutting oil used to aid in grinding. The grinding wheel is positioned and centred by inserting a properly sized pilot shaft into the valve guide. All valve guide service must be completed before installing the pilot. continued Copyright 2007 by Nelson