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| − | [[File:Jessel mohawk AFR ford windsor.jpg]][[File:Comp roller 374 ford sherman.jpg]]
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| − | ==Overview==
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| − | The valve train is one of the most important segments of any engine build. There can be no destructive contact/collision between any part of the reciprocating assembly and the valve train. And contact between any castings and the valve train has to also be avoided. Clearances have to be established and checked to be sufficient with the engine under operation up to its design limit.
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| − | ==Things that affect valve train clearances==
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| − | Many things can affect valve train clearances. When an engine is rebuilt or modified, often the block and/or cylinder heads will be milled to provide a flat surface with the correct finish for the head gasket to seal. If a different lift camshaft is installed, or if a different design or ratio rocker arm is used, or different length valves, resurfacing the valve and seats, different compressed thickness head gasket, changes to the stud boss height and/or installing guide plates or different design studs, lifter having a different measurement between the foot or roller and the pushrod cup, changes to valve spring installed height or diameter, or spring retainer and/or lock type, and different pushrod length all can change the clearances and geometry of the valve train. So if any of these things have been altered, the valve train clearance points need to be checked and verified to be correct. Manufacturing and tolerance stacking and wear can all change the exact measurements, so these things should be physically measured rather than figured using published figures.
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| − | ==Valve train geometry==
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| − | There needs to be a correct relationship between the components of the valve train to allow an efficient transfer of the cam lobe information into valve motion. This relationship is often referred to as the valve train geometry. On many OHV engines the geometry is adjusted by changing the length of the pushrod. A large number of variables are involved in determining the correct length pushrod for your application. Pushrod length is affected by any of the following:
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| − | *Block deck height
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| − | *Head deck height
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| − | *Head stud boss height
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| − | *Rocker arm brand/design
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| − | *Cam base circle size
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| − | *Lifter design/brand/pushrod seat height
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| − | *Valve stem length
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| − | *Head gasket thickness
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| − | ==Areas of the valve train that need to be checked and verified==
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| − | This list is not all-inclusive. Not all points will apply to all engine builds. There is no substitute for physically measuring critical areas like piston-to-valve clearances or valve spring installed height and coil bind. For those measurements, do not rely solely on published figures.[[File:Spring clearance diagram1.jpg|thumb|upright=3|Valve spring clearances]]
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| − | *Spring installed height
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| − | *Coil bind
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| − | *Retainer to seal/valve guide boss at full lift
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| − | *Retainer to rocker
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| − | *Trunnion to stud boss
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| − | *Piston-to-valve clearance (both before and after TDC on overlap)
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| − | *Push rod to guide slot in head
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| − | *Use '''EITHER''' self-aligning rockers '''OR''' pushrod guide slots in head '''OR''' guide plates, not two or more of these at the same time
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| − | *"Rails" of self aligning rockers to retainer
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| − | *Rocker to valve tip (by adjusting guide plates if used)
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| − | *Rocker slot to stud (if using stamped rockers w/pivot balls)
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| − | *Proper geometry
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| − | *Rocker arm/polylok to valve cover or oil baffle
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| − | *Camshaft endplay
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| − | *Distributor shaft and gear endplay
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| − | *Distributor gear material compatible with cam material
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| − | *Mechanical fuel pump pushrod material compatible with cam material
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| − | *Hydraulic lifter preload or solid lifter lash setting
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| − | *Timing set phasing
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| − | *Cam gear to crank gear alignment
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| − | *Cam gear end play if roller cam
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| − | *Cam gear to block casting/oil gallery plugs
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| − | *Timing set to timing gear cover
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| − | *If using the SBC OEM roller cam, lifters and retainers, the '''lobe lift''' must be kept below 0.354” so the lifter won’t lose contact with the retainers
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| − | *Cam lobe to connecting rod on strokers
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| − | [[Category:Engine]]
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| − | [[Category:Camshaft]]
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| − | [[Category:Adjust valves]]
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| − | [[Category:Good articles]]
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