Two bell cranks can transmit motion through projecting toes that bear against one another. Explore their opposed oscillation and calculate combined toe reach, nominal overlap and output-tip arc lengths from entered dimensions. Exact leverage depends on the contact profiles.
Declared Bell-Crank Toe Layout
Enter pivot spacing, equal toe projection, output-arm radius and inspection swing. Results are exact declared geometry, not a force or valve-timing prediction.
Equation Used
- Two rigid bell cranks have fixed pivots.
- Equal projecting toes face each other across the declared pivot spacing.
- The displayed oscillation is prescribed and symmetric.
- Contact pressure, friction, wear, force ratio and valve timing are excluded.
The pivots and arm lengths remain fixed as the bell cranks oscillate. The highlighted toe region illustrates where contact would occur; the animation does not solve the contact profile or force ratio.
Two bell cranks with opposing projecting toes
Hiscox movement 167 and the contemporary Scientific American reference describe two bell-crank levers whose projecting toes bear against each other. Swinging one lever causes the other to swing, with leverage varying as contact moves. The historical application stated is valve gear.
The animation keeps both pivots and arm lengths fixed and shows a prescribed opposed oscillation. The highlighted toe zone is qualitative because the historical source provides no dimensions or conjugate contact profile.
Historical valve-gear movement
Hiscox places this movement among valve-gear mechanisms. A projecting toe on one bell crank pushes against the other, with changing leverage as the contact point moves.
Bell-crank layout dimensions
These identities describe selected dimensions and a prescribed inspection swing. They do not calculate the movement's variable leverage or contact forces.
Declared example
For C=220 mm, t=120 mm, A=100 mm and alpha=15 degrees, combined toe reach is 240 mm, declared overlap is 20 mm, one-side output arc is 26.18 mm and the arc between swing extremes is 52.36 mm.
Model boundary
Exact motion and leverage require the actual toe profiles, contact normals, pivot geometry and valve linkage. Those data are not supplied by the historical caption.
The nominal overlap compares the combined toe reach with pivot spacing. It cannot establish continuous contact through a swing or determine the output force.
Toe-lever questions
Are these foot pedals?
No; the sourced movement is a pair of contacting bell cranks.
Does overlap determine mechanical advantage?
No.
Is the contact profile exact?
No; the rounded toe shapes illustrate the arrangement without solving mating contact profiles.
Does phase represent valve timing?
No.
Bell-crank toe-lever references
- Hiscox, Mechanical Movements, movement 167: pair of toe levers in the valve-motion sequence.
- Scientific American Handy Book, movement 167: two bell cranks with projecting toes in contact, variable leverage and valve-gear use.
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