⚙️ Valvetrain Dynamics

Compute effective valvetrain mass, required valve spring force to prevent float, and Hertzian contact stress on the cam lobe surface.

Valvetrain Mass Properties

Total reciprocating mass at the valve end
1/3 of spring mass counts as effective
From CAD or measurement (0 = no rocker)
Valve lift / cam lift (1.0 for direct-acting)
0 for OHC designs
Bucket, roller, or lifter mass

Valve Spring & Contact Properties

Installed force, valve closed (350 N ≈ 79 lbs)
Force per mm compression (35 N/mm ≈ 200 lbs/in)
Peak engine speed for dynamics analysis
Minimum radius of curvature at nose
0 or large = flat follower
Cam lobe width (axial)
📐 Formula Reference
Effective mass (valve side):
m_eff = m_valve + m_retainer + m_spring/3 + m_follower/R² + I_rocker/(R² × L²_valve)

Inertia force (on closing flank where acceleration is negative):
F_inertia = m_eff × a_cam(θ) × ω²_cam   (a in mm/rad², ω in rad/s → F in mN, convert to N)

Required spring force at each angle:
F_spring(θ) = F_preload + k × lift(θ)   must exceed   |F_inertia(θ)| on the closing flank

Hertzian contact stress (line contact):
σ = √( F × E* / (π × L × R*) )
where E* = E/(2(1−ν²)),   R* = R_cam × R_follower / (R_cam + R_follower),   L = contact width
For flat follower: R* = R_cam (nose radius)