I have recently become the owner of a Cowells 90ME lathe. It's about 30 years old, but has been almost unused. It's driven by its original single-phase TEFC synchronous motor. The motor's maker's/ratings plate has been removed. I would guess <1/3hp. It has a capacitor, in circuit all the time (no centrifugal switch), but its value is obscured by paint. The electrical details are hopefully irrelevant, because the problem is that the motor emits a very high-pitched, constant squeal, when run in either direction.

Dismantling reveals the expected construction. One pre-load wavy washer. All is clean – no corrosion, dust or discoloured lubricant weeps. The shielded ball bearings feel 'right'. No evidence of anything rubbing or races turning, etc. The motor feels absolutely fine, when spun by hand. A single oil seal exerts a little drag. Loading the shaft axially and radially, under power, makes no difference.

So, anyone any idea why the wretched thing squeals? I've never come across ball bearings seeming OK, but noisy like this – but what do I know? I doubt that the bearings themselves are at fault. Can shields rub and squeak? I suppose I should replace the bearings, but before that – could it be anything else?

John, I'm fine with pedantry. Of course, you're right. Please excuse my terminological inexactitude – it's getting late here on the opposite side of the world. Now that we've got its name sorted out, any idea why it squeals?

Thanks everyone for your suggestions.

Bearing in mind (apologies…) the age of the bearings, it seemed a good idea to replace them, so in went a pair of Polish NSK 6201ZZCM. The 'M' clearance rating is supposedly tighter than the C3 rating commonly available here, and is considered good for motors – quiet-running. Chinese bearings avoided – some must be fine, but which?

Motor reassembled with well-greased seal. Silence – for 30 seconds, then Squeeeek. Not the bearings then… With a hook probe, I was able to flick the seal's spring off whilst the motor was running – silence! The seal is a muck-keeper-outer, not an oil-keeper-inner, so the spring is accessible on the outside. So Mark is right – it was the seal! The removed bearings spin 'nicely', but with less grease drag than one would expect, so it was a good idea to replace them.

Inspection of the seal with a magnifier revealed that there was a matt cylindrical land, about 1.5mm axial length, in place of the expected sharp lip. The shaft was unmarked. This isn't a seal failure due to wearing-out, because of such little running time, but presumably due to the spring pressure over 30 years having caused the rubber to deform. Perhaps also long periods of disuse allowed the seal to adhere to the shaft, so that its surface was torn off at the next start.

I've not come across this before, but perhaps it's a well-known failure mechanism. Anyway, the thread is now here for anyone who searches for a solution to a squeaky motor.

Hopper – Absolutely! Some plastics are the wonder, neverlasting material industry's salesforce has been looking for. I've had many plastic components deteriorate or even disintegrate within a couple of decades of purchase. I usually replace seals after any dismantling that will have disturbed their relationship to the shaft, etc. The new bearings went in with the original seal because I couldn't immediately find a replacement that I thought I had in stock*.

Howard – I agree about the seal. What surprised me is that I really don't think the seal wore out 'normally', but that the main problem was that it deformed during 30 years of minimal activity. Perhaps it stuck to the shaft and its surface ripped at each infrequent start. Of course, once it was in a configuration where lubricant was squeezed out, it wore quickly – and noisily.

Muzzer – had I been able to get bearings with non-contact seals, I would have fitted them, if only for better lubricant retention. Some conventional bearing seals exert much more drag than others, but you can't test them in sealed packets very easily, so I stuck with the single, external, easily replaced seal. The poor little motor is rated at only 1/8hp.

* It eventually turned up, of course, exactly where it should have been.