Sheave sizing, belt length, chain pitch, and chain length for the Red Seal Industrial Maintenance Mechanic (433A) exam — Block D.
mwredsealprep.ca · Industrial Maintenance Mechanic 433A · Block D
Belt and chain drive calculations appear in Block D and test your ability to calculate speeds, select components, and determine centre distances. The math is straightforward — the challenge is keeping driver and driven components straight and using the right formula for the right drive type.
Belt drives use sheave diameter. Chain drives use sprocket teeth. The speed ratio formula is the same for both.
Output Speed
Input speed × (Driver diameter ÷ Driven diameter)
Required Driven Sheave
Driver diameter × (Input speed ÷ Output speed)
Open Belt Length
2C + 1.57(D + d) + (D − d)² ÷ 4C
Belt Length Variables
Can you solve drive calculations under exam pressure?
Test yourself with timed Red Seal–style belt and chain problems.
Try to solve each problem before revealing the solution.
Worked Example
Belt SpeedProblem
A 6" driver sheave on a 1,750 RPM motor drives a fan with an 18" sheave. What is the fan speed?
Worked Example
Sheave SizeProblem
A motor runs at 1,750 RPM with a 5" driver sheave. You need to drive a pump at 700 RPM. What driven sheave diameter is required?
Worked Example
Belt LengthProblem
A drive has a 12" driven sheave and a 4" driver sheave with a 24" centre distance. What belt length is required?
Output Speed
Input speed × (Driver teeth ÷ Driven teeth)
Chain Pitch from ANSI#
Chain number ÷ 8 = pitch (inches)
Chain Length (approx)
(N₁ + N₂) ÷ 2 + 2C/p — round up to even
ANSI Chain Pitch Reference
Chain Length Variables
Try to solve each problem before revealing the solution.
Worked Example
Chain SpeedProblem
A 17-tooth drive sprocket at 900 RPM drives a conveyor with a 34-tooth sprocket. What is the conveyor sprocket speed?
Worked Example
Chain PitchProblem
What is the pitch of a #60 roller chain?
Worked Example
Chain LengthProblem
A #50 chain (0.625" pitch) connects a 17-tooth sprocket to a 34-tooth sprocket with a 20" centre distance. How many links are required?
Chain Sag — Horizontal Drives
Proper chain sag is 2–3% of the centre distance, measured at the midpoint of the slack side.
Example: 30" centre distance → sag = 0.6" to 0.9"
Too tight increases sprocket and chain wear. Too loose causes vibration, noise, and possible jumping. For drives with reversing or shock loads, use less sag (tighter tension).
Open vs crossed belt formula
High RiskThe belt length formula is for open belts only. Crossed belt drives use a different formula. The exam will specify which type.
Chain length — round up to even
High RiskAlways round chain length up to the nearest even number. An odd-link chain requires an offset (half) link, which is weaker than a standard connecting link.
ANSI chain pitch — always divide by 8
Watch OutChain number divided by 8 = pitch in inches. This is always imperial, regardless of where the chain was manufactured.
Belt tension — over-tensioning is common
Watch OutOver-tensioning loads bearings and shortens belt life. Correct deflection is 1/64" per inch of span. Exam troubleshooting may present over-tension as the root cause of premature failure.
Belt drives use diameter, not radius
Watch OutUse full diameter measurements in all belt formulas. Using radius is a very common arithmetic error.
Randomized belt and chain problems — try to solve before revealing the answer.
Practice Problem
Randomized every time
Solve This
A 19-tooth drive sprocket runs at 1750 RPM and drives a 76-tooth sprocket. What is the output speed?
Last updated: June 2026 · Based on the Red Seal Occupational Standard (RSOS) for Industrial Maintenance Mechanic (Millwright) 433A
Belt and chain drives are one part of the 433A exam. Build your knowledge across all six Major Work Activities.
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