Ashley Slater wrote:

.....I thought I would have a play with my existing pump. ....... It always ran hot, casing too hot to hold. I have taken it apart and I can't get the rotor out of the windings they seem to have expanded

I have had that problem with a motor or two and it has always been rust on the rotor. The running clearance is only a few thou and it's very easy to get that much rust if the motor has stood in a damp environment for a while. I now always smear the rotor with an old greasy rag before reassembly in the hope of giving a bit of protection in future.

Ashley Slater wrote:

......... Got it back together OK and have tried running it on a small inverter, runs fine much quieter having oiled the top bearing bush but it still runs far too hot, after 5 mins it is too hot
to hold. So I am assuming it is terminal

If it runs and the inverter doesn't complain with a fault I suspect it is probably fundamentally OK, it just needs 'something' fixing. You could try an insulation test since it popped the RCD, but I suspect an inverter would also notice and give an error code if it were truely faulty. A Megger Tester would be the preferred choice, but a decent DVM should be able to show the insulation at a good few megohms and I would be happy enough with that. Disconnect the capacitior if you have one first or you may end up getting false readings as the DVM charges the C.

Thanks Bill, Richard. It's not rust on the rotor, I could persuade it past the windings but that would damage them which I suspect may have happened. When I say too hot I mean too hot to handle without gloves and my hands are pretty tough.   But I'll drag the Megger out (old wind up one) and see what sort of results I get. It's the damage to the fins on the end of rotor which are a mystery, looks like a bolt had been screwed in too far whilst the thing was running but there are no holes screwed or otherwise in the casing, damage was definitely  done whilst it was running. The pump  is from my mill and the previous owner looked to be a bit of a machine collector (radial arm saw in the garden) and other machines were far from pristine the pump could have been modified in some way but any changes are not obvious. The pump body is badly corroded internally.  It's a Carter of Romford - quite old now.  Here is a link to a photo but not a lot you can see from the outside https://dl.dropbox.com/u/79348422/SudsPump2.jpg
I have now put the 3 phase pump from my lathe on the mill just to see and am running it from an inverter.  I am now of the opinion the old pump has never been right it always got hot, was difficult to persuade it to pump in the first place and made a rattling noise whilst running, I put the rough running down to the capacitors to provide the third phase which was probably not right.  The lathe pump will have to go back on to the lathe next week but I now know that an ordinary 3 phase pump will work on either machine.
I have had the Megger (turning the handle at 160 RPM !) and my AVO.I have measured  Insulation between winding and earth(case) and the winding resistance
Winding 1 Insulation - infinite (OK?) winding 245 Ohms.
Winding 2 Insulation 800K ohms   winding 340 ohms
Winding 3  Insulation 600K ohms    winding 240ohms.
Looks to me as if insulation has broken down on two of the windings, but I'm no expert with a Megger.
Ashley

I don't know if your original pump was single or 3-phase, but I had a similar problem with a 3-phase suds pumps on a Colchester lathe which I had been operating with the aid of a static Transwave 3-ph converter. I don't know if the pump was running hot, because I never felt it as it was concealed in the lathe base. But the issue cost me a pump re-wind and I have continue to warn people of this problem ever since.

The original Colchester wiring configuration linked the suds pump, via a selector switch which was always on in my case, directly to the 3-ph 'line in' from the static converter. I accept not that everyone likes water based coolant on their cherished machines, but I am a great believer in flooding the work with coolant, as most 'professional' machines are designed to deliver, so when I started the main motor the suds began to flow. When I cut the main motor the suds stopped. Because of this I believed the suds pump was isolated from the converter along with the main motor. Nope!!

When I started the main motor again the suds flowed, no problem. What was actually happening was that when the main motor started the 'boost' on the converter was tripped and the suds pump ran quite happily in parallel with it. When I stopped the main motor and the full starting phase shift appeared at the output of the converter, the suds pump did not continue to run and did not have the characteristics sufficient to trip the start 'boost' on the converter and merely oscillated silently increasing in heat until it did this once too often and burnt out.

When I realised what had caused this failure I immediately reconfigured the wiring to make sure the re-wound suds pump was on the 'broken' side of the breaker, not the 'line' side. Since then there has been no further problems, but you all need to be aware of this issue.