This is a request for help from the mechanically minded on the forum
I am repairing a very nice Circa 2007 JBC JT6040 professional hot air station. The unit is in 'as new' condition but sadly has an issue with its air pump. The pump works, but makes some not too healthy noises when running. It appeared to have dry or gummed up Oilite bearings and weird intermittent vibrations. An initial inspection showed the motor to have low hours on it but there were issues. The brushes are not in correct alignment with the witness marks on the commutator and actually extend beyond the commutators rear edge ! With no brushes fitted the motor turned but was not free spinning so the Oilite bearings did need some attention. I will refurbish them later in a cleaning and 'oil refilling under vacuum' process that I have used to good effect previously. As a quick test I applied some new thin oil to the Oilite bearings and they immediately responded to the treatment. The motors armature became free spinning and felt more 'normal’. Confirmation that the oil in the Oilite bearings has either dried out or become thickened with age. The unit was made in 2007 and not used for many years so kept in storage.
Now that the Oilite bearings were working well, I re-assembled the pump for a quick test before changing anything else. The pump was much better behaved and less noisy but there was still an intermittent vibration and noise that just did not sound like it belonged in an expensive JBC rework station. Whilst I could live with the unusual sound the pump makes, it is a sign that something is wrong so part of me wants to repair it. The noise could be the symptom of something that could damage the pump over time and these pumps are VERY expensive from JBC.
I dismantled the pump to expose the internal parts. I then inspected the rotor and the pumps air compression chamber for faults, debris and witness marks of rotor to compression chamber wall contact. Nothing disastrous could be seen but the issues I did notice were as follows:
1. The regenerative pumps rotor is in very close proximity to the air intake port on the motor side of the compression chamber housing. Almost perfect alignment of the housings parts is needed to avoid contact and scraping of the rotor on the compression chamber intake port edges. This may be 'by design' but could be the strange noise that I am hearing and vibration from the pump when running.
2. There was evidence of minor contact between the rotors central boss area and the compression chambers central ‘end stop’ face. Contact had, or is occurring during operation.
3. The pumps rotor is a typical regenerative pump design and no fins are missing or damaged but the rotor is slightly warped in the Z axis. This could be the cause of intermittent contact with the compression chamber inlet pot that is a 'high point' in the compression chambers interior surfaces.
4. The issue with the brushes and commutator alignment has already been mentioned but I analysed what could be seen to establish a potential cause. The whole motor armature appears to have shifted towards the regenerative fan assembly. I can see such occurring if the motor was dropped either before installation into the JBC hot air station or whilst the complete appliance was in transit. Witness marks on the commutator from brush contact suggest that the brushes were once correctly positioned on the commutator so this is not a manufacturing defect. Wear on the brushes show a small lip where they now overhang the commutator rear edge. This issue occurred some time ago and not whilst the unit was in transit to me. I found a picture of another JT6040 pump and the motors shaft extends well beyond the rear bearing assembly by approx 2 to 3mm. My motors shaft is flush with that bearings rear face. Could the motor have been dropped on its rear and the shaft driven forwards maybe ? There is no obvious long term damage but this situation should be rectified and may be a symptom of another, more serious, issue in the motor. In order to become out of alignment the armature has either moved down its central shaft or the whole shaft assembly moved. It is the latter in this case as there is excess clearance in the end float washers at the commutator end of the shaft. This suggests that the bearing housing at the regenerative pump end of the motor has been distorted by the impact of the heavy armature hitting it in a fall event. The movement also pushed the central shaft further through the pumps rotor hub as there is little lateral movement possible in the regenerative pump compression chamber.
So now we come to my challenge. How can I remove the pumps plastic rotor without damaging it or the motor ? The rotor is made from a nylon like material but it is harder than nylon. the compression chamber is made of a hard plastic like a very tough, but possibly brittle, ABS.
Approaches that I have considered are:
1. Holding the compression chamber housing and tapping the motors shaft with a small hammer after warming the rotors central boss to soften it and reduce the chances of cracking - tried this, no movement on the shaft.
2. Pulling on the compression chamber that acts upon the rotors central boss, after warming rotor - tried this. No movement
3. Placed string under the rotor and pull rotor off of shaft after warming - tried this. No movement
4. Apply some sort of gear puller to the rotor - this would be a challenge due to lack of clearance between the rotor and the compression chamber plus it risks damaging the rotor fins.
5. Place the compression chamber in a vice and drift the motor shaft out with a small hammer. This may work but is not without risks as the hammer impacts can damage the housing and even shock the armature into moving down its shaft !
6. Place a thin metal sheet in a the space available between the motor mount and compression chamber (around 2mm) and build a compression frame on it to press down on the motors shaft to push it out of the rotor whilst the rotor presses against the compression chamber central boss. A threaded push bar/drift does the work and is a controlled force compared to the impacts of a hammer and associated shock waves. This is my favoured approach due to the control I would have on the applied forces but it fails on the basis that I can only use a 2mm metal plate to pull against and that will undoubtedly bend during the application of the compression force on the motors shaft.
If/when I have removed the pump rotor from the shaft, I will dismantle the motor and correct any distortion in the bearing housing(s) before giving the motor a full lubrication and alignment service. I will refit the regenerative pump rotor using a padded jaws vice and a suitable socket to place over the central boss. With such an arrangement I can carefully position the rotor on the motor shaft for clearance within the compression chamber walls.
Right now I would welcome any suggestions or advice on how best to process with the removal of the rotor from the motors shaft. There is a hole passing through the shaft but no evidence of any fixings used to secure it so it appears to be a very tight push fit but could also be held by and adhesive that cannot be seen on the exposed side of the rotor. The adhesive bond would have been broken when the shaft moved however.
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