JBC JT6040 regenerative pump repair & service detail inc. Oilite Bearing refill - Page 1
Forum section: electronics / repair

author: Fraser
author_rank: Super Contributor
timestamp: February 20, 2021, 03:17:47 pm
content: This is a request for help from the mechanically minded on the forumI 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 movement3. Placed string under the rotor and pull rotor off of shaft after warming - tried this. No movement4. 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.

author: Fraser
author_rank: Super Contributor
timestamp: February 20, 2021, 03:18:51 pm
content: Pictures continued....

author: Fraser
author_rank: Super Contributor
timestamp: February 20, 2021, 03:26:10 pm
content: A picture of another JBC regenerative air pump with the motors shaft clearly visible extending beyond the rear Oilite bearing by an amount comparable to the brush offset seen on my pumps commutator. Further evidence that the whole armature has moved forwards towards the pump end of the assembly. This will have destroyed the end float pre-loading design of the motor so that the end float becomes controlled by the pump rotor and its clearance with its compressor housing central bosses either side of it. Not a great and likely why the pump sounds 'weird' when in operation. Friction in the rotor to compressor housing interfaces would not be good in the long term for this pumpFraser

author: Fraser
author_rank: Super Contributor
timestamp: February 20, 2021, 03:34:56 pm
content: Detail of my pumps rear bearing area showing the the motor shaft position, brush overhang and excess end float visible adjacent to the commutator.All comments and advice welcomedFraser

author: Fraser
author_rank: Super Contributor
timestamp: February 20, 2021, 04:20:07 pm
content: I have begun a search for a replacement ‘Universal’ motor in case the original has to be sacrificed or is badly damaged. The original is made by ‘Sun’ and hopefully a standard format so a replacement can be sourced that matches the dimensions. I also need to confirm the motors voltage and will do so by checking the drive waveform from the speed controller and RPM at maximum drive signal.I attach a motor that, whilst not the same, shows the likely front bearing housing design that I believe has been distorted. It is fortunate that it is steel, so bent, unlike cast aluminium that cracks ! It is a pity that the motor end bearing housings are secured with a screw from the front and not the rear. I could have then dismantle to motor to get access to the armature for rotor removal operations. I could unwind the visible screw thread at the rear with my stud removal pliers but such an operation is risky.Fraser

author: Fraser
author_rank: Super Contributor
timestamp: February 20, 2021, 04:30:51 pm
content: This motor on Alibaba costs $5 plus delivery. If it were the same as the one I need it would be around $400 cheaper than a JBC replacement air pump ! That is quite a saving !Fraser

author: Fraser
author_rank: Super Contributor
timestamp: February 20, 2021, 04:58:51 pm
content: Before anyone asks...... I do not see any evidence of a thread on the motors shaft and it looks to be plain with a hole through it that is empty.Fraser

author: Fraser
author_rank: Super Contributor
timestamp: February 20, 2021, 05:02:44 pm
content: Johnson Electric are big players in the motors market so I shall investigate their offerings in case they have something suitable. Thankfully they have datasheets on-line to view.https://www.johnsonelectric.com/en/product-technology/motion/ac-motors/universal-motorsFraser

author: Fraser
author_rank: Super Contributor
timestamp: February 20, 2021, 06:13:33 pm
content: Hmmmm life gets more fun by the minuteThere appears to be no metal bearing holder at the front of the motor ! There is, in its place, a bearing holder made from the same material as the pump housing. That is to say a very hard, potentially brittle plastic. So what does this mean ? Well if there is no metal to become distorted, we are faced with the real possibility that the Oilite bearing was driven into the plastic holder by a force acting upon the armature shaft and the result may have been breaking the plastic bearing holderIf that is indeed the case, I will definitely need to dismantle this motor and repair the damage.I am leaning wards pressing the armature shaft out of the pump rotor as the most controllable method of rotor removal. The combination of heating and increasing pressure on the shaft will hopefully ease it out. I just need to construct a jig to do the task.Fraser

author: nali
author_rank: Frequent Contributor
timestamp: February 20, 2021, 06:33:21 pm
content: It's a bit difficult to tell from the photos, but pic 1120997 in your OP suggests that you may be able to put a pair of screwdrivers one each side to keep it level and pop the rotor + shroud together off the end of the armature?

author: Fraser
author_rank: Super Contributor
timestamp: February 20, 2021, 06:38:42 pm
content: NaliThanks. That is another possibility. I will look into itFraser

author: Fraser
author_rank: Super Contributor
timestamp: February 20, 2021, 06:47:55 pm
content: Hmmm, looking at the pump again, it would appear that the front bearing may be in the wall of the compression chamber and not in the plastic bracket on the front of the motor ! Unusual design but it means I cannot lever between the motor print bracket and the compression chamber casing.Fraser

author: nali
author_rank: Frequent Contributor
timestamp: February 20, 2021, 07:11:51 pm
content: A thought just occurred to me - don't you still have your X-Ray machine so you can get a handle on how the hidden parts are constructed ?

author: Fraser
author_rank: Super Contributor
timestamp: February 20, 2021, 08:01:31 pm
content: Success! The fan has been removed without damaging anything..... but it was a pig of a job.The attempt to push the motors drive shaft out failed with no visible movement for the force that I was willing to apply. The shaft appeared to be stuck fast in the fanI decided to take a calculated risk and introduce Mr Motor shaft to Mr Stanley, my trusty hard headed friend and his mate, The DrifterAfter building a supporting jig for the compression chamber section in wood, I positioned the jig on a workmate bench and applied some persuasion with a few taps from Mr Stanley on the end of Mr Motor shaft. Absolutely no effect ! Mr Stanley is not one to be beaten so he upped his game and some heavier blows rained down on Mr Motor shaft. This had the desired effect and Mr Motor shaft cowered inside the fan assemblyAt this point The Drifter came on scene and a combination of blows from Mr Stanley via Mr Drifter provided the desired result and Mr Motor shaft was evicted from the fan. No harm came to any involved party !A translation for anyone confused.... I drifted the motor shaft (Mr Motor Shaft) out of the fan using a hammer (Stanley) and suitably sized drift (The Drifter) !The reason for the failure of my previous attempts was clear. The fan has a central boss that is driven into a ball race assembly and the Motor shaft is then driven into the fans central boss. That central boss is so long that heating the visible area of the boss has no effect. The boss was so tight on the motor shaft that it fought me all the way until the shaft was out !Pictures attached.I will add pictures of the motor disassembly later to help others working on these units.Fraser

author: Fraser
author_rank: Super Contributor
timestamp: February 20, 2021, 09:06:58 pm
content: The pictures of the motor disassembly, as promised.The motor will be given a gentle clean and inspected for any issues. The Oilite bearing will be refurbished to new state. The motor will then be carefully reassembled and clearances set. The brushes will need to be dressed to maintain the correct profile whilst removing the small lip that was created when the motor commutator was not properly aligned to them.Once rebuilt the regenerative motor should run sweetly and the correct clearances should ensure a long operation life for the fan and motor.Fraser

author: Fraser
author_rank: Super Contributor
timestamp: February 20, 2021, 09:08:06 pm
content: Pictures continued.....

author: Fraser
author_rank: Super Contributor
timestamp: February 20, 2021, 09:09:27 pm
content: Pump end detail.....

author: Fraser
author_rank: Super Contributor
timestamp: February 20, 2021, 10:19:00 pm
content: One final comment on the JBC regenerative pump ...... considering the original cost of the JBC JT6040 hot air station and the pump as a spare part....... I am not impressed with the pumps design. It is a flawed design and the motor section is just a typical cheaply made universal motor. The preloading washer and ball bearing race configuration at the pump end of the design is frankly cr*p.I note that JBC have now moved to the 'snail shell' type air pump in more recent designs. Hopefully that pump is better designed and uses a higher quality motor section.Fraser

author: Fraser
author_rank: Super Contributor
timestamp: February 21, 2021, 05:26:43 pm
content: An update on the work I have done on the JBC pump and associated "SUN" universal motor1. The motor armature has been inspected and cleaned. The drive shaft and commutator were then polished.2. The ball bearing race in the wall of the compression chamber was tested and found to be still serviceable with no noises to cause any concern for its condition. It is a a quality NKE 6000Z deep groove type bearing.3. It was noted that the black plastic end plate of the motor that butts up to the NKE bearing did not sit perfectly flat against the side of the compression chamber, as it should. This meant that it was not fully pressing the NKE bearing into its seat in the compression chamber. This could cause issues with the pumps rotor position within the compression chamber and lead to contact between the fan and the casing around it. The cause of the issue was found to be the presence of raised molding lines at the middle and edges of the plastic motor end plate. The end plate was resurfaced on P600 and then P1200 grade wet&dry paper and is now flat. The NKE bearing is pressed fully into its seat4. The Oilite rear bearing in the motor was examined under a microscope and a lack of lubricating oil in the sintered bronze 'pores' was noted. The bearing is not worn but requires a full service to return it to new condition. I am in the process of carrying out that service and will detail the process that I use below.Servicing a sintered bronze "Oilite" bearing :a) I first submerged the bearing assembly in IPA overnight as an initial cleaning stage.b) The bearing assembly was dried with warm air and the bearing placed in a vacuum chamber at -600 mmHg to draw out material from the Oilite bearings pores. It was then briefly immersed in IPA and dried to remove contaminants.c) The whole bearing assembly was submerged in Acetone after testing the resistance of the brush holders to that solvents actions. No softening of the very hard brush holders was noted. The Acetone is a very efficient solvent for the removal of mineral oils. The Acetone immersion lasted 1 hour and the bearing was then removed and placed in a -600 mmHg vacuum to draw out any oil from the bearings pores. The bearing was then immersed in acetone for a second time but for only 10 minutes. This process should have effectively removed the original oil from the Oilite bearing.d) Some Castrol GTX 15W50 Mineral motor oil was placed in a small jam jar that was then immersed in boiling water. this was indirect heating of the Mineral oil to thin it ready for loading into the Oilite bearing. The Oil was heated until almost too hot to touch and then poured into the vacuum chamber. The Oilite bearing assembly was lowered into the heated oil and a vacuum of -600 mmHg applied to the chamber. Almost immediately bubbles of air could be seen coming out of the Oilite Bearing and this is exactly what was expected. The air is pulled out of the sintered bronze material by the vacuum and is replaced with nice fresh Catrol GTX mineral oilThe amount of air coming out of the bearing caused a 'froth' on the top of the oil. Once the air extraction was competed the froth disappeared. The vacuum was quickly release by disconnecting the hose. The vacuum chamber was sat in a container of water at 80C to keep the oil warm during the next stage in the process. The vacuum was then reapplied at -600 mmHg and the bearing observed for any air bubbles coming from its surface.None were seen so the bearing should now be filled with nice fresh oil. The bearing will remain in the oil in a vacuum of -600 mmHg for 2 hours.I attach pictures of the vacuum chamber arrangement that I use. It is made using nothing more sophisticated than a car brake system vacuum bleeder. These are not expensive but can apply a vacuum of -600mmHg which is perfect for tasks such as Oilite bearing refurbishmentI have used it for other tasks where application of a vacuum is needed. Well worth having one in the garage.Once the Oilite bearing oil filling stage is completed, I will clean the metal bracket and brush holders of all oil and then begin reassembly of the motor.Fraser

author: Fraser
author_rank: Super Contributor
timestamp: February 22, 2021, 11:24:23 pm
content: Another update on the JBC JT6040 pump repairI have just competed reassembly of the Regenerative Pump from my JBC JT6040 and thought others might be interested in how it went. There was an expected issue that I have resolved to my satisfaction. Read on for more....The refilling of the Oilite bearing with oil went as planned and it was time to reassemble the pump module for testing.The challenge was going to be how to refit the fan boss onto the motors shaft without damaging the fan. I decided to use a combination of a soft jawed wide mouth engineering vice, an 11mm 1/2" drive socket form my socket set and some care ! The 11mm socket was placed over the fans central boss so that the force was applied very close to the boss in order to avoid distorting the fan or cracking it. As I clamped the 'sandwhich' of the motor fan and 11mm socket in the vice, I carefully aligned it for equal force to be applied to the fan on all sides. As the vice was tightened the fan moved down the shaft and I was able to carefully set its position to that which gave me correct commutator to brush alignment plus a small amount of space between the commutator, spacer washers and Oilite bearing. There is virtually no end float in the motor due to the armature position being dictated by the fan assembly NKE 6000 ball race that holds the shaft in place. Once I was happy with the fan positioning it was time to refit the outer casing of the fan module and test fit the cover on the regenerative fan. I was expecting an issue and sure enough I had one.the fan now cleared the rear half of the compression chamber despite thee being some run-out on the fan Z axis, but that run-out caused the fan to make contact with the front half of the compressor chamberI believe this was occurring when I originally rested the JBC station as it certainly sounded like something was rubbing inside the pump.So.... how to fix the problem ? Well the fan cannot easily be brought back into true and the run-out is relatively small. Those familiar with Regenerative pumps will know that they can be quite forgiving in terms of the compression chamber dimensions and small changes to such. With this in mind I decided to provide clearance for the warped fan by adding a gasket, or two to the joint between the two halves of the compressor chamber. I have some artists thin black card that is 0.27mm thick and so perfect for the task of increasing the fan clearance. After making the two gaskets I tried one and discovered that there was still some contact so the second gasket was fitted. The fan then spun without any contact wit the compressor chamber walls. so I needed just over 0.5mm of 'packing' using the gaskets to achieve fan clearance. The fan is now ready to return to service.I attach pictures taken during the reassembly. Note the new position of the carbon brushes on the commutator, the clearance space between the commutator, spacer washers (oil slingers ?) and Oilite bearing. The end of the armatures shaft now protrudes out of the Oilite Bearing instead of being flush with it. This was the amount by which the shaft had been incorrectly positioned and had applied an end load on the thrust washers at the other end of the motor. Those washers were suffering damage as a result. All is well now and the thrust washers are, to be honest, made obsolete by the use of the ball bearing race that holds the armature in place.All good funFraser

author: Fraser
author_rank: Super Contributor
timestamp: February 22, 2021, 11:25:41 pm
content: Pictures continued......