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Presentation on theme: "BASIC ENGINE TESTING."— Presentation transcript:


2 Four Stroke Cycle Intake stroke Piston going down - intake valve open.
Low pressure created in cylinder. Volumetric Efficiency maximum at w.o.t. Compression stroke Piston going up - both valves closed. Mixture squeezed to increase combustibility, molecules, raises temp. Needs good seal to compress and combust. Power stroke Piston going down - both valves closed. Work is performed by expanding gasses. Exhaust stroke Piston going up - exhaust valve open. Exhaust gasses exit. Any exhaust left over dilutes incoming a/f mixture with inert gas (exhaust) Causes poor quality and quantity of charge.

3 Valves Valves serve two purposes:
Sealing - during compression and power strokes Opening up of ports - during intake and exhaust strokes

4 Cylinder Sealing Performed by tight seal of valve face against seat to seal in compression pressures Most common loss of compression is valve not sealing properly

5 Broken Valve Spring Valve not fully closed

6 Bent Valve Bent due to piston contact

7 Burned Valve Face burnt due to poor contact with seat (leaking)

8 Proper Valve & Seat Position
Guide Seat Face

9 Opening of Valves Controlled directly or indirectly by camshaft

10 Volumetric Efficiency
Three factors affect VE: How far the valve opens (lift) The amount of time that it is open (duration Size of opening A problem with valve opening will affect volumetric efficiency or the quantity of incoming fuel mixture

11 Multiple valves Multiple valve heads will act same as big valve heads
Secondary throttle plates can be used to eliminate loss of ram effect

12 Lobe Lift & Duration Lift - How far valve will open
Duration – How long it stays open

13 Head Design Wedge style most common, cost effective design
Hemi style very efficient air flow, expensive Porting & polishing increases air flow, less restriction & reduced turbulence in ports

14 Carbon Buildup Carbon build up on intake valve Flat cams
Worn valve guide/seal (oil) Fuel deposits Affects V.E. Flat cams Valve doesn’t open fully

15 Testing

16 Vacuum gauge testing Provides quick test for compression problems
Should read 15-20” of manifold idle Cranking vacuum will be 3-5”

17 Vacuum Testing Measures vacuum level in intake manifold
Indicator of basic engine condition

18 Normal Ave., steady readings between 15 – 22 in Hg

19 Leaking Rings Low but steady, 12 – 15 in Hg, late ignition timing, late valve timing

20 Single Cylinder Misfire
Fluctuations between 1 & 2 in Hg Possible burned valve

21 Sticking Valve Irregular needle drop between 1 & 3 in Hg.
Multiple cylinder misfire – rich or lean mixture

22 Weak Valve Springs Normal at idle Excessive vibrations at higher rpm
Sticking valve guides

23 Worn Valve Guides Excessive vibrations at idle Steadies at higher rpm

24 Leaking Head Gasket Excessive vibrations at any rpm
Loss of compression

25 Leaking Intake Needle oscillates slowly, drifts between 3 & 9 in Hg.

26 Restricted Exhaust Normal at idle
Drops near 0, may rise to lower than normal

27 Cranking Compression Test
Used for checking engine seal Must set up conditions W.O.T., bat. charger, disable ignition, all plugs out Compare readings - 10% max difference Typical range: psi Wet test is performed when cranking compression is low Add SMALL amount of oil to cylinder, helps seal worn rings

28 Leak Down Test Used to identify location of sealing problem
Cylinder must be at TDC, comp. stroke Problem is detected if loss is greater than 20%

29 Identifying Location of Leak
Air escaping through exhaust, open valve Air escaping through intake, open valve Air escaping through valve cover, worn piston rings Air escaping through radiator, blown head gasket

30 Running Compression Test
Test cylinder seal at idle Readings will be low, less time to fill cylinder Compare readings - no specs Identifies compression loss apparent while running Broken valve springs Worn valve guided Burned valve

31 Snap Compression Test Tests for problems with v.e.
Allows rush of air at relatively low rpm, nearly filling cylinder which will cause increased compression pressures If a cylinder has a restricted intake snap pressures will be lower Compare readings - no specs

32 Improper Valve Lash Too little will cause sealing problems
Too much will cause excessive noise, wear and loss of lift

33 Valve Lash Adjustment


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