Valve train inspection Inspect... Cylinder head castings Valves Guides Springs Cam and lifters Rocker arms and push rods Timing chains and gears Copyright 2003 Gary Lewis – Dave Capitolo

Valve train inspection Cylinder head castings Visual inspection – Anything inconsistent Gasket surfaces – Fire rings, water ports Crack detection – Magnaflux, dye penetrant Flatness –.004” Go/No Go on deck surfaces Top side of OHC – Cam rotation

Valve train inspection Valves Stem wear -.001” to.0015” Margins – 1/32” or ½ new thickness Necking on stems Tulip valve heads Straightness – When refacing

Valve train inspection Valves Keeper groove wear Stem tip wear caused by rotator failure

Valve train inspection Valve burning Starts with unequal cooling Warpage, then burning

Valve train inspection Valve springs Pressure – 10% of spec in closed position Square – Within 1/16” for each 2” of length Pitting & corrosion

Valve train inspection Valve guides Measure wear limit: Stem diameter + max clearance Valve rock is not the same as guide clearance! Rock is more than clearance

Valve train inspection Valve guide knurling limits Measure stem diameter. Is it within limits? Set telescoping gauge: stem dia ” +.004” Use as “Go/No Go” If wear is excessive, replace guide or use OS stem

Valve train inspection Rocker arm studs Threads Nicks on the side of studs Height within 1/32”

Valve train inspection Push rods Straightness, length, & end wear Some signs of wear on sides may be normal Push rod guide holes in head

Valve train inspection Rocker arms Wear on faces & push rod sockets Wear in adjusting screws Stamped rockers cannot be refaced Forged, cast, & fabricated rockers can be refaced

Valve train inspection Rocker shafts Cleaning is critical for normal oiling Check direction of oil holes

Valve train inspection Cams and lifters Inspect lifters for rotation Inspect cam lobes for wear

Valve train inspection What makes lifters rotate? Crowned lifter base Tapered cam lobe Taper is.001” to.002”

Valve train inspection More cam & lifter wear Edge wear on cam lobes Pitting on lifter bases

Valve train inspection More cam & lifter wear Good pattern is a narrow path near center of lobe Wear may extend across full width of lobe

Valve train inspection Cam lobe wear limits Measure cam lift of all lobes Variations should be less than.005” for exh. or int.

Valve train inspection Cam journal wear Measure journal diameters with micrometer Check cam bore on aluminum heads for wear

Valve train inspection Lifter testing Test predetermined leak down Finds excessive clearance and check valve failure Lash compensators (OHC) checked the same way

Valve train inspection Natural gas valve trains No lubrication in fuel Valve rotators should be removed Recommended valve material - Inconel alloy Recommended seat material – cobalt, non-magnetic Recommended seal material - Viton umbrella seals

Valve train inspection Timing components OHV timing chain slack – Maximum ½” Timing gear backlash – Maximum.006”

Valve train inspection Timing components OHC timing chain slack – Controlled by tensioners Worn assemblies rattle at start up and at idle