How to disassemble gearbox of DC motor? - Page 1
Forum section: electronics / repair

author: Sypher
author_rank: Contributor
timestamp: December 31, 2015, 11:32:45 pm
content: Not very EEVblog-ish but thought I'd try here anyways.would like to disassemble the gearbox, replacing all bearings/seals and remove rust from the shaft. Could someone give me an idea on how to go about disassembling it? For example, how would I remove the shaft? Does it twist off or pull off? Looking at the bearings, there is no way to get a puller anywhere. It is a full metal casing from a QUANTUM 600.I am trying to fully rebuild the motor and gearbox. I could probably do fine w/o replacing the bearings inside the gearbox; however, I would like to if possible.

author: tautech
author_rank: Super Contributor
timestamp: December 31, 2015, 11:46:10 pm
content: Best guess is both the output (splined) and the intermediate shaft are each retained with a circlip under the shaft seal and blanking cap.Carefully prise the shaft seal out taking care as to not damage the sealing surface of the shaft.Generally the seal will be damaged beyond repair depending on how this is done.There are specialist seal removers available but for a "oncer" they'll be cost prohibitive.Screwdrivers or seal picks are the normal tools of choice.

author: Brumby
author_rank: Unknown
timestamp: January 01, 2016, 03:02:21 am
content: I take it, this is what the full assembly looks like?

author: Brumby
author_rank: Unknown
timestamp: January 01, 2016, 03:41:21 am
content: First question: Is there an 'overhaul kit' available for this gearbox? If so, there is a possibility of there being some instructions - which would be rather useful - but even if there is not, the fact that an overhaul kit exists would indicate this is a job that is doable. I went looking for images/diagrams of an exploded view of the gearbox, but the best I could find showed the gearbox as a single unit.I'm not familiar with gearboxes like this, but it is clear any removal of blanking caps or output shaft seal must be done with care to ensure you don't damage the sealing surfaces.Also, the casing is a casting of (by the look of it) aluminium, which means you should be careful where and how much pressure you apply in any prising or you might crack it. This is not to say it won't stand up to a bit of pressure, just be mindful of what you're doing.The one thing I would like to know is how much 'end float' (longitudinal movement) there is in each of the shafts - and if there is any, where that movement occurs. Look very closely because even a miniscule amount could provide some useful information.As for the retaining mechanism for the shafts,tautechcould be right. I would 'pick out' the output shaft seal (it's going to get destroyed anyway) and see what's underneath. There is also the possibility that the shafts may be a press fit inside the bearings. Whatever you find there is probably what you will find under the blanking caps.Again, not knowing what to find, I would not be surprised to find the bearings themselves to be a press fit into the casing. IF this is the case, you might find yourself in for a challenging exercise. Pressing bearing into a casing is easy. Getting them out is not.If it were me, I could clean out all the grease from the gears and have a closer look to see if there are any clues on assembly. If I was comfortable taking the next step, I would carefully remove the output shaft seal (already having a replacement available) and check once more.

author: Richard Crowley
author_rank: Super Contributor
timestamp: January 01, 2016, 03:50:28 am
content: You didn't mention whether the bearings actually need replacement, or whether you just thought it might be a fun exercise? Given the appearance of the construction, it would appear that while you probably could remove and replace the bearings, the actual cost of doing that quite possibly exceeds any benefit by a considerable degree.

author: tautech
author_rank: Super Contributor
timestamp: January 01, 2016, 04:32:00 am
content: Quote from: Brumby on January 01, 2016, 03:41:21 amAs it was originally unknown if the "offside" was capped or shaft bearings were into blind holes the images in the OP provided, yours offer many clues along with careful study of the OP's images. In those circlips on each shaft can be seen but they're not for shaft retention per se but to hold components in the correct position on each shaft. They each will need to be removed for disassembly and to do so right angle circlip pliers must be used. I'd suspect each shaft assembly was pressed together as part of the process of installation and while not rocket science the methodology will need be thought out.As the gearbox itself will be reasonably low speed, I'm with Richard and unless the bearings are fubar I'd repack with a quality grease (marine?) and return to service.

author: SeanB
author_rank: Super Contributor
timestamp: January 01, 2016, 09:47:53 am
content: Looks like the bearings are both a press fit and glued in, so removal will need a set of special tools to apply pressure to the right areas on the case and the inner race at the same time, which will be rather terminal to the bearing. If you need to do this you will need some fairly good tooling made to do it, and a new gearbox might work out cheaper. Otherwise just a repack with some molyslip CV joint grease will give a good increase of life, and will keep it quiet for a while. Gears are a little worn, but still usable, so fill up 1/3 with grease and put back together, and leave alone till it finally fails.

author: vodka
author_rank: Frequent Contributor
timestamp: January 01, 2016, 08:06:01 pm
content: For the web there are many places where teaches you as extracting shafts , gears and bearings with homemade tools, if you can't to find the specific tool or these are very expensivesExampleshttps://youtu.be/_NlIqfDOt9Uhttps://youtu.be/28bSl4r1kwQhttp://www.gti16.com/usr/coco/gg_restauracio/gg_restauracio.html

author: cncjerry
author_rank: Unknown
timestamp: January 02, 2016, 12:33:15 am
content: The bearings are probably press-fit. There might be a retaining clip but it would be obvious. You need a press to disassemble the unit.It is not unusual for people afflicted with engineering like us to want to 'take it apart' to clean it, etc. I've seen it a bunch of times as I also have a Vespa. As this is obviously a slow-speed unit, unless the bearings are frozen, I would wash it out, and repack it to the original level.If you must take it apart, use a press but also heat the unit to reduce the required pressure assuming the seals can be removed.

author: AF6LJ
author_rank: Unknown
timestamp: January 02, 2016, 12:53:07 am
content: The gear on the right in this picture seems to be badly worn.

author: tautech
author_rank: Super Contributor
timestamp: January 02, 2016, 12:58:54 am
content: Quote from: AF6LJ on January 02, 2016, 12:53:07 amIt's not, it's the crownwheel of a worm gear drive reduction.

author: AF6LJ
author_rank: Unknown
timestamp: January 02, 2016, 01:08:42 am
content: Quote from: tautech on January 02, 2016, 12:58:54 amOkay; works for me.

author: Gyro
author_rank: Super Contributor
timestamp: January 02, 2016, 10:36:27 am
content: That gearbox looks to be in excellent condition. there may be the odd bit of surface rust on the external shaft but no indication of seal problems or any water ingress into the bearings. No signs of wear and the grease look clean and uncontaminated.Is there actually a problem you're trying to fix?

author: oldway
author_rank: Super Contributor
timestamp: January 02, 2016, 10:54:04 am
content: In this kind of reducer, the first thing that tends to wear out is the Archimedes screw gear of the motor shaft.It seems in good condition and It would surprise me very much that the bearings are damaged.Unnecessarily disassemble this gearbox can cause problems that did not existe before.

author: SeanB
author_rank: Super Contributor
timestamp: January 02, 2016, 11:05:56 am
content: Not as bad as this one was..

author: Brumby
author_rank: Unknown
timestamp: January 02, 2016, 12:22:55 pm
content: Quote from: Gyro on January 02, 2016, 10:36:27 amI had wondered about this also ... but didn't think to ask the obvious question:Quote.... and there is exceptionally great wisdom in this comment:Quote from: oldway on January 02, 2016, 10:54:04 am

author: Richard Crowley
author_rank: Super Contributor
timestamp: January 02, 2016, 04:31:58 pm
content: It appears that most (all?) of us are recommending AGAINST any attempt to remove/replace the bearings.But the OP appears to be a newbie hit-n-run poster and has never returned to clarify his question.

author: vodka
author_rank: Frequent Contributor
timestamp: January 02, 2016, 06:07:36 pm
content: i believe that the photos of the gearbox are bads. if it sometimes is hard to find the circlicks on clear gears,at a gears with grease is a nightmare.i recommended you, before to do the photos ,you clear the gears with a agricultural cleaner or with other degreaser.

author: G7PSK
author_rank: Super Contributor
timestamp: January 03, 2016, 05:40:23 pm
content: If that is a wheel chair motor, I think you will find the gears are fixed to the shaft's with pin's. Knock them out and then drive the shaft out which will take the blanking plug with it. That was how my wife's wheel chair gear boxes were made when I took an old one apart.

author: cncjerry
author_rank: Unknown
timestamp: January 04, 2016, 06:29:15 am
content: I believe we've scared the OP away.I was looking for pins as well but didn't see any. You would think they'd be obvious.

author: G7PSK
author_rank: Super Contributor
timestamp: January 04, 2016, 09:12:25 am
content: Quote from: cncjerry on January 04, 2016, 06:29:15 amObscured by the grease, if you look at the bigger gear you can see two places a pin might be hiding under the grease, one is a semi circle just seen on the top of the gear flange the other is a dimple to the left a bit.

author: Gyro
author_rank: Super Contributor
timestamp: January 04, 2016, 09:32:06 am
content: Probably not worth pursuing any further guys. The OP hasn't been back to answer any questions.

author: Eng_hassan85
author_rank: Newbie
timestamp: March 01, 2016, 10:24:17 pm
content: Quite interesting Topic