Cylinder Head: Springs, Valves, and Valve Seats Chapter 8 Cylinder Head: Springs, Valves, and Valve Seats

Objectives Analyze wear and damage to valves, springs, and seats Understand theory related to valves, seats, springs, and other related parts Select and perform correct repair Reassemble cylinder head

Valve Springs Pressure on valve spring comes from three sources Spring Pressure of combustion Seat angle

Valve Spring Inspection Visual inspection Spring squareness Free length Spring tension

Pushrods Transmit motion from lifters to rocker arms Hollow to allow oil to be transferred to rocker arms Holes in cylinder head act as guide for push rod

Pushrods

Rocker Arms Shaft mounted or stud mounted Iron, cast iron, or stamped steel Different ratios (longer length) Increasing ratio causes more movement of valves Makes it possible to have smaller cam lobes

Rocker Arms

Valve Damage Wear on valve stem Valve burning Hoop stretching Valve oxidation Incorrect seating due to incorrect valve lash

Exhaust and Intake Valves Intake valves are generally larger than exhaust High carbon steel and tempered to resist corrosion Valve stems are typically chrome plated Some are sodium filled

Grinding Valves Chamfer valve tips Grinding stem tip Should be done before grinding valve Grinding stem tip .010" to .015" should be removed from valves Grinding valve face 1º interference angle

Grinding Valves

Grinding Valve Face First dress grinding stone Adjust chuck to grab valve on unworn section of valve stem Do not allow neck of valve to contact grinding stone

Grinding Valve Face Adjust grinder to proper valve angle Grind only enough to remove any area of valve face that is worn

Valve Seats and Service Most valve seats are integral and part of the cylinder head Integral seats are induction hardened to reduce seat wear Operate approximately 150º cooler than replaceable valve seats

Grinding or Cutting Seats Most are finished to 45º or 30º Seats are serviced with either grinding stones or carbide cutters Pilot is installed into valve guide to center cutter

Grinding or Cutting Seats

Grinding Seats Advantages of grinding Produces a smoother seat than cutting does Can be used on extremely hard seats Grinding stones must be dressed to true them to proper angle Valve seat runout should be less than .002"

Grinding Seats

Carbide Cutters Advantages to carbide cutters Quiet Remain clean Angles remain true No grinding dust

Carbide Cutters

Seat Refinishing Angles Sometimes all three angles are cut at once, which also cuts seats to correct height. Typical three angle valve job Face angle Top angle Throat angle

Seat Refinishing Angles

Reassembling Cylinder Head Recheck installed height of valve spring Grind tip or install new valves to achieve proper specification Install valve shims under springs

Reassembling Cylinder Head Thoroughly clean all guides Lubricate valve stems Install guide seals Install valve, spring, retainer, and keepers