Valve train points to check

==Overview==

==Overview==

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.  

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.  

==Things that affect valve train clearances==

==Things that affect valve train clearances==

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.  

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.  

==Valve train geometry==

==Valve train geometry==

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:  

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:  

==Areas of the valve train that need to be checked and verified==

==Areas of the valve train that need to be checked and verified==

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.

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.