Valve train inspection Inspect... Cylinder head castings Valves Guides Springs Cam and lifters...

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


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


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


Valves• Keeper groove wear• Stem tip wear caused by rotator failure


Valve burning• Starts with unequal cooling• Warpage, then burning


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


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


Valve guide knurling limits• Measure stem diameter. Is it within limits?• Set telescoping gauge: stem dia. + .002” + .004”• Use as “Go/No Go”• If wear is excessive, replace guide or use OS stem


Rocker arm studs• Threads

• Nicks on the side of studs• Height within 1/32”


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


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


Rocker shafts• Cleaning is critical for normal oiling• Check direction of oil holes


Cams and lifters• Inspect lifters for rotation• Inspect cam lobes for wear


What makes lifters rotate?

• Crowned lifter base• Tapered cam lobe• Taper is .001” to .002”


More cam & lifter wear

• Edge wear on cam lobes• Pitting on lifter bases


More cam & lifter wear

• Good pattern is a narrow path near center of lobe • Wear may extend across full width of lobe


Cam lobe wear limits

• Measure cam lift of all lobes• Variations should be less than .005” for exh. or int.


Cam journal wear

• Measure journal diameters with micrometer• Check cam bore on aluminum heads for wear


Lifter testing

• Test predetermined leak down• Finds excessive clearance and check valve failure• Lash compensators (OHC) checked the same way


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


Timing components

• OHV timing chain slack – Maximum ½” • Timing gear backlash – Maximum .006”


Timing components

• OHC timing chain slack – Controlled by tensioners• Worn assemblies rattle at start up and at idle

Valve train inspection Inspect... Cylinder head castings Valves Guides Springs Cam and lifters...

Documents

Transcript of Valve train inspection Inspect... Cylinder head castings Valves Guides Springs Cam and lifters...