Five free practice questions on bearings, drives and shaft alignment: block C of the Red Seal 433A Industrial Mechanic Millwright exam, about 32 of its 135 questions. They are in the exam's format: four options, one correct answer. Answer each one before opening the explanation. No account, no email.
01The questions
-
A pillow block on a mine crusher is oil-bath lubricated. With the shaft at rest, to what level should the oil be filled?
- Just touching the bottom of the shaft
- The centre of the lowest rolling element
- The centre of the shaft
- The bottom of the outer ring
Show the answer
B. Correct. In an oil bath the static level is set at about the centre of the lowest rolling element. That is enough for the elements to pick up oil and carry it through the bearing, but not so much that the rollers plough through oil and churn it, which generates heat and foam. The sight glass or level plug on a properly designed housing is positioned for this level.
Why not the others
A. At that level the whole bearing is submerged. The level is set much lower, at the middle of the bottom element.
C. Oil to the shaft centre submerges half the bearing and causes churning heat at normal speeds. That level is far too high.
D. At the bottom of the outer ring the rolling elements do not reach the oil and the bearing runs dry. The level must reach the middle of the bottom element.
-
In the reverse dial indicator method, what do the two indicators read?
- The motor feet and the base
- The rim and the face of the same coupling hub
- The gap between the hub faces at top and bottom
- Each shaft's rim, from a bracket on the other shaft
Show the answer
D. Correct. A bracket on the motor shaft carries an indicator reading the rim of the pump hub or shaft, and a bracket on the pump shaft carries one reading the motor rim; both shafts are turned together and the two rim readings are taken at the same positions. From the two rim offsets and the distance between the indicator planes, the angular and offset misalignment at the coupling and the moves at the feet are calculated. It is preferred for long spans, since sensitivity increases with the distance between the indicators, and it is unaffected by face runout and axial float.
Why not the others
A. An indicator on the feet is the soft foot check. Reverse dial reads the shafts.
B. Rim and face on one hub is the rim-and-face method. Reverse dial uses two rim readings, one on each shaft.
C. The gap is a face reading, taken in the rim-and-face method or with feelers in rough alignment. Reverse dial takes no face readings.
-
An auto plant paint-shop fan is vibrating and the operator blames the motor. What is the quickest way to establish whether the vibration originates in the motor or in the fan?
- Replace both motor bearings and recheck
- Run the motor uncoupled and measure again
- Increase the grease charge in the motor bearings
- Realign the coupling and see if it improves
Show the answer
B. Correct. Running the driver alone separates the two machines. If the motor vibrates by itself, the fault is in the motor (rotor imbalance, bearing, soft foot); if it runs smoothly, the source is the fan wheel, its bearings or the coupling and alignment. This is the standard first test before any component is condemned, and it takes minutes.
Why not the others
A. Replacing parts before locating the fault is guesswork. If the fan wheel is the source, the new bearings change nothing.
C. Grease does not correct imbalance or misalignment, and over-greasing creates its own heat problem.
D. Realignment without a diagnosis may mask or move the problem. Isolate the source first, then correct what you find.
-
An overhead crane hoist at a steel mill must hold its load if power is lost. Which brake arrangement provides that?
- Hydraulically applied by the operator
- Electrically applied, spring released
- Spring applied, electrically released
- A centrifugal brake on the motor shaft
Show the answer
C. Correct. A fail-safe holding brake is applied by springs and held off by an electromagnet (or a thruster or solenoid) while the hoist is powered. Loss of power, a tripped drive or an e-stop releases the magnet and the springs set the brake, so the load cannot run away. The same principle is used on inclined conveyors and elevators. The brake is checked for release clearance and spring force on the PM.
Why not the others
A. A manually applied brake depends on the operator reacting to a power loss. A hoist brake must set by itself.
B. A brake that needs power to apply drops the load the moment power is lost. The arrangement must be the reverse.
D. A centrifugal device acts on speed, not on the loss of power, and cannot hold a stationary load.
-
A vibration analyst asks the millwright for the gear pass (mesh) frequency of a reducer input stage at a pulp mill. The pinion has 24 teeth and turns at 1 750 rpm. Using the exam formula sheet, what is the gear pass frequency?
- 84000 cpm
- 1750 cpm
- 42000 cpm
- 10500 cpm
Show the answer
C. Correct. Gear pass frequency = rpm × number of teeth = 1 750 × 24 = 42 000 cycles per minute, which is 700 Hz. Every tooth of the pinion meshes once per revolution, so the meshing impulse repeats 24 times per turn. On the spectrum, a rising peak at this frequency with sidebands spaced at the shaft speeds points at tooth wear, misalignment or eccentricity in that mesh; the mating gear gives the same mesh frequency because the same teeth pass.
Why not the others
A. 84 000 cpm is twice the mesh frequency (2× GMF). Counting both gears' teeth, or doubling for the mating gear, leads to this mistake; the mesh frequency is the same for both gears.
B. 1 750 cpm is simply the shaft speed (1× rpm). Gear pass frequency multiplies the shaft speed by the tooth count.
D. 10 500 cpm is 1 750 × 6, a slip in the arithmetic. With 24 teeth the product is 42 000.
02Answer key
| Question | Answer | Sub-task |
|---|---|---|
| Q1 | B | Maintains shafts, bearings and seals |
| Q2 | D | Performs dial alignment |
| Q3 | B | Diagnoses prime movers |
| Q4 | C | Installs couplings, clutches and brakes |
| Q5 | C | Diagnoses gear systems |
03What block C covers
This block covers the drive train from the motor to the driven machine. It includes electric motors and steam turbines, rolling-element and sleeve bearings, lip and mechanical seals, rigid, gear, jaw, disc and fluid couplings, clutches and brakes, V-belt, timing belt and roller chain drives, gearboxes and gear lubrication, and shaft alignment by straightedge, dial indicator and laser, including soft foot and thermal growth.
The Red Seal Occupational Standard names this block “Services mechanical power transmission components and systems”. It carries 23.7% of the exam, about 32 of the 135 questions, split across six tasks. The share column is each task's weight within the block, as the standard publishes it.
| Task and its sub-tasks | Share of block |
|---|---|
| Services prime movers Installs prime movers; Diagnoses prime movers; Maintains prime movers; Repairs prime movers | 16% |
| Services shafts, bearings and seals Installs shafts, bearings and seals; Diagnoses shafts, bearings and seals; Maintains shafts, bearings and seals; Repairs shafts, bearings and seals | 20% |
| Services couplings, clutches and brakes Installs couplings, clutches and brakes; Diagnoses couplings, clutches and brakes; Maintains couplings, clutches and brakes; Repairs couplings, clutches and brakes | 16% |
| Services chain and belt drive systems Installs chain and belt drive systems; Diagnoses chain and belt drive systems; Maintains chain and belt drive systems; Repairs chain and belt drive systems | 15% |
| Services gear systems Installs gear systems; Diagnoses gear systems; Maintains gear systems; Repairs gear systems | 16% |
| Performs shaft alignment procedures Performs rough alignment; Performs dial alignment; Performs laser alignment | 17% |
04What the questions turn on
Soft foot comes first
Correct soft foot before taking alignment readings, dial or laser, or the readings will not repeat. A foot sitting on a stack of thin, dirty shims is squishy soft foot: rebuild it with no more than three or four clean shims.
Reading the dials
A rim reading swept from top to bottom is twice the centreline offset, so divide the TIR by two. In a valid sweep, top plus bottom equals left plus right. If it does not, find what moved and take the readings again.
Mounting rolling bearings
The ring that rotates relative to the load gets the interference fit, usually the inner ring. Press only through the ring being fitted, or the balls dent the raceway. Heat bearings to about 80 to 110 °C, never above roughly 120 °C.
Chains, sprockets and belt sets
Measure ten pitches under light tension; past about 3 % elongation the chain is replaced. Check the sprockets too, because hooked, undercut teeth wear out a new chain in weeks. A multi-belt V-belt drive needs a matched set.
05The other blocks
The 433A exam has six blocks. Each has its own page of free questions:
The 433A Industrial Mechanic Millwright practice exam page describes the full question bank. How these questions are written and checked: how our questions are made. Found a mistake? Tell us and we will fix it.