Presentation 1

ENGINE VALVE AND VALVE SEAT (AUTOMOBILE) GROUP 1

PRESENTATION ON VALVE REFACING AND VALVE SEAT GRINDING Presented to: Mr. Rajan KarirAssociate Prof. UCE, RTU, KOTA 1

VALVE AND VALVE SEAT

2Valve is a device to close and open a passage . In motor vehicle engine mainly two valves are used for each cylinder an inlet valve and an exhaust valve. What is valve..?

3The INTAKE VALVE is larger than the EXHAUST VALVE because the intake charge is being drawn into the combustion chamber at a low speed due to differences in pressure between atmospheric pressure and the pressure (vacuum) inside the cylinder. The exhaust is actually pushed out by the piston and, therefore, the size of the valve does not need to be as large, leaving more room in the cylinder head for the larger intake valve.

Inlate and exhaust valve

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3D view of valve

5Plan and side view of valve

6Inlet valves is usually made of nickel chromium alloy steelExhaust valve is made of an alloy of silicon and chromium steel which is a corrosion and heat resisting materialExhaust valve is subjected to more heat then the inlet valve so material used for exhaust valve is silchrome steel which has an abnormal heat resisting property

Material selection for valve7Valve sticking take place due to the gum or carbon deposits on the valve stemExcessive valve stem clearance speeds up valve depositsin every stroke , the oil will be pulled through this clearance into the combustion chamber where it will burnValve troubles1)valve sticking-

8This causes excessive oil consumption , engine deposits, pre ignition , clogged piston rings and fouled spark plugsAnother cause of valve sticking is warped stem , due to over- heating , eccentric seat and cocked spring or retainerValve sticking also take place due to insufficient oilSometimes , valve will stick when cold but will work free as the engine warm up

9Valve burning may take place due to any condition that prevents normal exhaust valve seating Poor seating speeds up valve heatingIf water circulation around the valve seat is clogged , it will cause over-heating of valves2)Valve burning

10engine overloading or overheating will also heat the valve A lean air-fuel mixture causes valve burning . In this cause, the fuel system should be servicedSometimes valve burning occurs due to guttering. This is caused by carbon deposits on the valve face and seat.Parts of the deposits break off to form a path through which exhaust gas can pass when the valve is closed

11If there is excessive valve tappet clearance , the tappet will strike the valve like hammer If the seat is eccentric to stem or if the valve spring or retainer is cocked then the valve will be subjected to side movement every time its seats . This will cause it to fatigue and break3)Valve breakage

12Valve face wearing takes place due to the excessive tappet clearance or dirt on the valve face or seatExcessive tappet clearance causes heavy impact seating i.e. wearing on the valve and it may cause valve breakage also.4)Valve face wear

13Excessive rich mixture , improper combustion , defective ignition, loss of compression are the causes of carbon deposits on the valve5)Valve deposits

14There comes a time in the life of every valve when it must either be replaced or reconditioned. Valve face become worn and eroded as the seats wear , the stems wear where they contact the guides, and the tips of the stem can become worn or mushroomed from the constant friction with the rocker arms or cam followers Need for valve refacing and valve seat grinding15Heat also play a roll on the valves the hotter the valve run they undergo undesirable metallurgical changes.Exhaust valve runs hundreds of degree hotter than intake valve and may experience burning or failure if the valve makes poor contact with the seat or guide.Engine overheating because of a cooling problem or lean fuel condition may be a contributing factor16This process is done by a machine known by its name This machine consists of grinding wheel operated by an electric motorThe valve is held in chuck which can be moved at any angle

Refacing

17Put the valve into the chuck and tighten it. Move the face of the valve across the valve grinding wheel

18This is a procedure done to restore the valve and valve seatsAt every overhauling of engine valve seat must be inspectedDue to usage of poor quality fuels and etc , the valve seat may get pitted , get more wide etc. by cutting valve seat and grinding this problem may be rectifiedThe valve seat may be cut using a valve seat grinderThe valve seat cutter fitted on the valve seat, moves along valve guideThe tool is rotated by hand by means of sliding handle provided at the top

Valve grinding19Grinding stone and wheel dresser

20Valves are refinished on face angle using a valve grinder

Grinding wheel is dressed with an industrial diamond

Very little metal is removed from surface of the valve face

Valve grinding

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SPECIFICATIONS THAT ARE TO BE CHECKED IN CASE OF VALVE FAILURE

22Valves wear: oil consumption results Measure the valve stem with a micrometer

Checking valve stems

23Springs are tested for:Tension & HeightSpecifications are available in the service manual

Checking valve springs

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