Motor replacement — what to measure and how to find a match
The motor is dead, the nameplate is gone, no documentation — and you need a replacement. Sound familiar? We handle this every day, sometimes 3–5 times. Finding the right replacement takes 10–15 minutes once you know what to measure and where to look.
Step 1: collect data from the old motor
Even without a nameplate the motor tells you its story through dimensions:
- Shaft centre height (H) — from foot base to shaft centre. This is the key dimension defining frame size: 71, 80, 90, 100, 112, 132, 160, 180, 200, 225, 250 mm.
- Shaft diameter (d) — use a calliper. For example, 19 mm = frame 80, 28 mm = frame 112, 38 mm = frame 132.
- Foot-hole spacing — between mounting bolt centres (L and B). Determines whether the new motor fits the existing base.
- Body length — S, M, or L (short, medium, long).
- Mounting type — foot (B3), flange (B5), combined (B35).
If the nameplate is partially legible — write down everything: power, speed, voltage, current, cos phi.
Step 2: determine power and speed
Without a nameplate:
- From shaft height and diameter — cross-reference with the AIR frame table
- From current — measure with a clamp meter. P ≈ U × I × √3 × cos φ × η / 1000
- From the driven equipment — the pump or fan datasheet states the required motor power
Step 3: find the equivalent
| Old series | AIR equivalent | WEG equivalent | ABB equivalent |
|---|---|---|---|
| 4A100L4 (3 kW) | AIR 100L4 | W22 100L 4P | M2AA 100L |
| 4AM132M4 (11 kW) | AIR 132M4 | W22 132M 4P | M2AA 132M |
| 4AM160S4 (15 kW) | AIR 160S4 | W22 160M 4P | M3BP 160M |
| AI160M4 (18.5 kW) | AIR 160M4 | W22 160L 4P | M3BP 160L |
| 4AM200L4 (45 kW) | AIR 200L4 | W22 200L 4P | M3BP 200L |
Note: replacing a Soviet 4A with AIRM may not fit — AIRM has a smaller frame at the same power. Verify mounting dimensions before ordering.
Step 4: verify compatibility
- Shaft height — must match within ±1 mm, otherwise the foundation needs shimming
- Shaft diameter and length — if the old coupling stays, the new shaft must fit
- Mounting holes — foot-bolt spacing. If different — you need an adapter plate
Import motors (DIN/IEC) may differ from AIR dimensions. WEG W22 and ABB follow IEC, which does not always match GOST. At frame 132 and below the difference is minimal; at 160+ it can be noticeable.
When to upsize
- Motor burned from overload — step up one power rating (e.g. 7.5 → 11 kW)
- Equipment upgraded — higher output requires higher motor power
- Adding a VFD — a VFD optimises operation, so the same or even lower power may suffice
Upgrading AIR → WEG
If the old AIR motor worked fine but you want better efficiency — WEG W22 IE3 makes sense above 11 kW on continuous duty. IEC mounting dimensions match AIR for most frame sizes.
Do not scrap the old motor
- Rewinding — 40–60% of a new motor cost. For large motors (30 kW+) often the better deal.
- Spare parts — bearings, fan, terminal box may be in working condition.
- Scrap value — copper winding has value.
Frequently Asked Questions
Motor is dead, nameplate unreadable — what do I do?
Measure shaft centre height and shaft diameter. These two numbers determine the frame size. Then use the AIR table to identify power. Or send us a photo — we will figure it out.
Can I replace a Soviet 4A with a modern AIR?
Yes, mounting dimensions match for most frame sizes. AIR is the direct successor of 4A.
How much does a motor replacement cost?
AIR 7.5 kW — from 5,000 UAH. WEG W22 — from 12,000 UAH. Installation — from 2,000 UAH. Alignment — from 1,500 UAH.
Rewind or new motor — which is cheaper?
Up to 15 kW — a new motor is usually better (rewind costs 60–80% of a new AIR). Above 30 kW — rewinding is often cheaper and faster.
How long to wait for a motor on order?
Standard AIR sizes — in stock, 1–3 days. Non-standard WEG and ABB — 2–6 weeks.
Summary
Motor replacement is straightforward with the right measurements. Shaft height + shaft diameter + mounting holes determine 90% of the match. Send a photo of the old motor to our team and we will find the equivalent from the AIR or WEG catalog.
