BASIC ENGINE TESTINGFour Stroke CycleValvesCylinder SealingBroken Valve SpringBent ValveBurned ValveProper Valve & Seat PositionOpening of ValvesVolumetric EfficiencyMultiple valvesLobe Lift & DurationHead DesignCarbon BuildupTestingVacuum gauge testingVacuum TestingNormalLeaking RingsSingle Cylinder MisfireSticking ValveWeak Valve SpringsWorn Valve GuidesLeaking Head GasketLeaking IntakeRestricted ExhaustCranking Compression TestLeak Down TestIdentifying Location of LeakRunning Compression TestSnap Compression TestImproper Valve LashValve Lash AdjustmentBASIC ENGINE TESTINGFour 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.Valves•Valves serve two purposes: •Sealing - during compression and power strokes •Opening up of ports - during intake and exhaust strokesCylinder Sealing•Performed by tight seal of valve face against seat to seal in compression pressures•Most common loss of compression is valve not sealing properlyBroken Valve Spring•Valve not fully closedBent Valve•Bent due to piston contactBurned Valve•Face burnt due to poor contact with seat (leaking)Proper Valve & Seat PositionFaceSeatGuideOpening of Valves•Controlled directly or indirectly by camshaftVolumetric 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 mixtureMultiple valves •Multiple valve heads will act same as big valve heads•Secondary throttle plates can be used to eliminate loss of ram effectLobe Lift & Duration•Lift - How far valve will open•Duration – How long it stays openHead 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 portsCarbon Buildup•Carbon build up on intake valve–Worn valve guide/seal (oil)–Fuel deposits–Affects V.E.•Flat cams–Valve doesn’t open fullyTestingVacuum gauge testing•Provides quick test for compression problems•Should read 15-20” of manifold vacuum @ idle•Cranking vacuum will be 3-5”Vacuum Testing•Measures vacuum level in intake manifold•Indicator of basic engine conditionNormal•Ave., steady readings between 15 – 22 in HgLeaking Rings•Low but steady, 12 – 15 in Hg, late ign. timing, late valve timingSingle Cylinder Misfire•Fluctuations between 1 & 2 in Hg•Possible burned valveSticking Valve•Irregular needle drop between 1 & 3 in Hg.•Multiple cylinder misfire – rich or lean mixtureWeak Valve Springs•Normal @ idle•Excessive vibrations @ higher rpm•Sticking valve guidesWorn Valve Guides•Excessive vibrations @ idle•Steadies @ higher rpmLeaking Head Gasket•Excessive vibrations @ any rpm•Loss of compressionLeaking Intake•Needle oscillates slowly, drifts between 3 & 9 in Hg.Restricted Exhaust•Normal @ idle•Drops near 0, may rise to lower than normalCranking Compression Test•Used for checking engine seal–Must set up conditions•W.O.T., bat. charger, disable ign., all plugs out–Compare readings - 10% max difference–Typical range: 110 - 150 psi•Wet test is performed when cranking compression is low–Add SMALL amount of oil to cylinder, helps seal worn ringsLeak 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%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 gasketRunning 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 valveSnap Compression Test •Tests for problems with v.e.•Allows rush of air @ 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 specsImproper Valve Lash•Too little will cause sealing problems•Too much will cause excessive noise, wear and loss of liftValve Lash