Removing PTFE Sleeve Bearings

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Removing PTFE Sleeve Bearings

Home Forums Workshop Tools and Tooling Removing PTFE Sleeve Bearings

Viewing 25 posts - 1 through 25 (of 32 total)
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  • #242690
    Ben Jones 5
    Participant
      @benjones5

      Hi, I'm new here. I've got a problem in that I need to be able to remove, replace, and potentially resize some 32mm ID/35mm OD PTFE lined aluminium backed bearings. They are fitted to a blind hole and located about 130mm from the opening. Can anyone recommend whether a tool exists for this type of job or whether I would be better having something made up…

      Many thanks,

      Ben.

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      #18123
      Ben Jones 5
      Participant
        @benjones5
        #242704
        Michael Gilligan
        Participant
          @michaelgilligan61133

          Now that's an interesting puzzle, Ben

          slippery stuff, PTFE … so you're almost certan to damage it before any expanding tool will grip.

          Question: Is the bearing really at the bottom of the hole, or is there some gap beyond?

          The [apocryphal?] 'hydraulic ram' trick might possibly work, but 130mm is a long way!!

          MichaelG.

          #242710
          Ben Jones 5
          Participant
            @benjones5

            Hi Michael, glad to have been of service!

            I did miss some detail earlier, the bearings do have gap beyond probably 30mm or so. Are you aware of any off the shelf engineering tools that can deal with this? One suggestion I received elsewhere was a shaped washer on a rod to be dropped just below the bearing and dragged out carefully with a slide hammer..

            Getting new bearings back in and sized could be even more interesting… Maybe a shaped drift. Very fine tolerances though, 32mm +/- 0.001mm for the sizing.

            Thanks,

            Ben.

            #242712
            Michael Gilligan
            Participant
              @michaelgilligan61133
              Posted by Ben Jones 5 on 13/06/2016 23:31:55:

              I did miss some detail earlier, the bearings do have gap beyond probably 30mm or so. Are you aware of any off the shelf engineering tools that can deal with this? One suggestion I received elsewhere was a shaped washer on a rod to be dropped just below the bearing and dragged out carefully with a slide hammer..

              .

              That should make it relatively easy … I'm not sure about the availability of off-the-shelf kit for this, but, for example, I have one special puller that expands a set of legs behind the bearing. … The shaped washer should work, and slide hammers are good; but determining the optimum shape & size of the washer could be tricky. Hopefully the old bearings are considered sacrificial.

              MichaelG.

              #242714
              Ben Jones 5
              Participant
                @benjones5

                Bearings definitely sacrificial on the way out. Will be back in touch if I find out any more.

                #242726
                Hopper
                Participant
                  @hopper

                  Can you heat the housing and slide the old bearings out using a suitable bearing puller etc?

                  #242733
                  not done it yet
                  Participant
                    @notdoneityet

                    Can you heat the housing and slide the old bearings out

                    Depends on the material. Aluminium fits tighter in steel as temperature rises. Better to freeze it possibly. A dewar of liquid nitrogen would easily do the trick, I suspect.

                    #242734
                    Ian P
                    Participant
                      @ianp

                      Aluminium backed PTFE sleeve bearing to a 0.001mm tolerance sounds a very unusual beast. It would help if we knew what is this bearing fitted to and how its is retained? If the housing is aluminium then extracting the aluminium bearing backing sleeve might be difficult because of the two surfaces galling.

                      How do you intend to do the resizing after fitting the new bearing anyway?

                      Ian P

                      #242741
                      Ben Jones 5
                      Participant
                        @benjones5

                        Hi, the bearings are fitted to a very old set of bike suspension forks. Not quite a model engine bit figured the use case was pretty similar. The fork lower tubes, where the bearings are fitted, are a magnesium alloy of some kind. Into the bearings slide the fork uppers. The bearings do seem a very tight fit on their outer radius, heating might be possible although would need to be very careful with the alloy.

                        ​I was hoping for some advice on the resizing part of this job, given the material is PTFE I was thinking tapered drifts of varying sizes could be used.

                        My internet research tells me that installation and resizing tools are very difficult to come by!

                        ​Thanks,

                        ​Ben.

                        #242743
                        Martin Kyte
                        Participant
                          @martinkyte99762

                          If you can seal the top of the upper fork leg you have a potential ram with which to extract your bearing. Goes something like this. Fill the lower leg to just above the bearing with oil. Fit the upper tube into the lower leg . Fully fill the upper leg and seal the top. Force the upper leg down into the lower leg maybe by thumping with heavy hammer padded with a lump of wood if you cannot arrange a press. The bearing should be forced up the lower leg. Maybe easier if you turned up a flanged bush to sit at the top of the lower fork leg to keep the whole assembly concentric.

                          regards Martin

                          #242746
                          Ian P
                          Participant
                            @ianp

                            Ben

                            If the replacement bearings are available surely the fork manufacturer will have fitting details? if the forks are so old they are no longer supported then you could research what other manufacturers recommend.

                            Are these PTFE bushes actually 'aluminium backed' or are they a composite of the two materials? I see that PTFE loaded tin bearings are made so maybe yours use aluminium instead.

                            Knowing what the application is I cannot understand why a tolerance of 0.001mm is being specified, seems overkill!

                            Ian P

                            #242750
                            Michael Gilligan
                            Participant
                              @michaelgilligan61133
                              Posted by Martin Kyte on 14/06/2016 09:06:14:

                              If you can seal the top of the upper fork leg you have a potential ram with which to extract your bearing. Goes something like this. Fill the lower leg to just above the bearing with oil. Fit the upper tube into the lower leg . Fully fill the upper leg and seal the top. Force the upper leg down into the lower leg maybe by thumping with heavy hammer padded with a lump of wood if you cannot arrange a press. The bearing should be forced up the lower leg. Maybe easier if you turned up a flanged bush to sit at the top of the lower fork leg to keep the whole assembly concentric.

                              regards Martin

                              .

                              dont know … That is, of course, "The [apocryphal?] 'hydraulic ram' trick" that I mentioned earlier.

                              I have a suspicion that we all "know a bloke who met somebody that knew a man that did this"

                              … But perhaps, Martin, you are that man

                              MichaelG.

                               

                              Edited By Michael Gilligan on 14/06/2016 10:10:24

                              #242755
                              Martin Kyte
                              Participant
                                @martinkyte99762

                                I should have said as mentioned earlier and I have done in on bushes with a bar end and grease. Don't see why it shouldn't work on a fork leg bush especially if it can be set up without too much trouble. Is there any form of retaining clip on the bush?

                                regards Martin

                                Is it apocryphal because the bush is 'hidden' down the fork leg.?

                                #242761
                                Michael Gilligan
                                Participant
                                  @michaelgilligan61133

                                  Martin,

                                  I'm impressed to hear that you have actually done this [so you are indeed 'that man'] star

                                  I do fear, however, that a magnesium alloy fork leg might burst before the bush moves 130mm crying

                                  MichaelG.

                                  #242765
                                  Martin Kyte
                                  Participant
                                    @martinkyte99762

                                    Why do you think that then Michael. Why should the leg burst before the bush moves. Do you actually think you can produce that amount of pressure?

                                    Martin

                                    #242766
                                    roy entwistle
                                    Participant
                                      @royentwistle24699

                                      Michael for nearly 30 years I used to remove oilite bushes from blind holes on printing machines using the hydraulic method    Believe me it works

                                      Roy

                                      Edited By roy entwistle on 14/06/2016 11:41:17

                                      #242767
                                      Ben Jones 5
                                      Participant
                                        @benjones5

                                        The apocryphal hydraulic ram trick sounds like a neat idea. The tops of the fork leg can be sealed no problem, although I feel that maybe attempting it whilst hiding behind a blast proof screen might be a good idea

                                        Looking at the bearings closer I see one problem with this and that is they're slotted to allow oil to blow past.

                                        The bushes are interference fit with no retaining clips. Interesting point about whether they truly are aluminium backed or PTFE composite – I'm not sure.The original manufacturer is in Switzerland – DT Swiss – and no longer holds spares but did indicate the bearings are not necessarily specific to this industry

                                        It seems that official manufacturer tools are very few and far between – and in most cases their recommendation is to replace the whole lower assembly where the bearings are already pressed in – seems a waste. Unfortunately due to the obsolescence within the cycling industry, forks of this particular size are no longer manufactured and therefore to throw the fork away means to throw the whole bike away…

                                        My subsequent research has found a handy guide provided by another fork manufacturer.

                                        **LINK**

                                        They use generic tools that can cater for a variety of bearing sizes. Looks like the bearing removal and replacement tool is available from USA, and is reassuringly expensive.

                                        #242769
                                        Chris Evans 6
                                        Participant
                                          @chrisevans6

                                          I have made glass filled PTFE fork bushes and the stated 0.001mm tolerance is questionable. I usually bore the bushes to plus 0.003" (0.075mm) above the stanchion size. Any less and the forks will not move. I would think the 0.001mm is from the bearing manufactures specification and the stanchions are undersize.

                                          #242785
                                          not done it yet
                                          Participant
                                            @notdoneityet

                                            Don't knock the method. Likely not work in ths instance if the cross section of the sleeve is minimal (suspect it may be).

                                            The method was used just two weeks ago on the engine of my daughter-in-law's car. They needed to remove the bush in the flywheel/crankshaft as this exchange engine accepted a smaller spigot shaft, than the gearbox to which it was to be fitted, and it had stymied the mechanics. They actually used bread as the 'hydraulic jacking medium'. The bush was extracted successfully – and quite easily in the end.

                                             

                                            Edited By not done it yet on 14/06/2016 14:04:43

                                            #242801
                                            Michael Gilligan
                                            Participant
                                              @michaelgilligan61133
                                              Posted by Martin Kyte on 14/06/2016 11:35:23:

                                              Why do you think that then Michael. Why should the leg burst before the bush moves. Do you actually think you can produce that amount of pressure?

                                              Martin

                                              .

                                              32mm diameter piston, driven hard enough to move a bearing with such a small end-area [wall-thickness is only 1.5mm] suggests some pretty high fluid pressures.

                                              Happy to be wrong; but I think a slide-hammer might be safer.

                                              All depends on how tight the bearing is fitted into the bore of the leg.

                                              MichaelG.

                                              #242803
                                              Michael Gilligan
                                              Participant
                                                @michaelgilligan61133
                                                Posted by Ben Jones 5 on 14/06/2016 11:49:44:

                                                The apocryphal hydraulic ram trick sounds like a neat idea. …

                                                Looking at the bearings closer I see one problem with this and that is they're slotted to allow oil to blow past.

                                                .

                                                In that case

                                                1. The slide hammer sounds a much better idea
                                                2. They may not be very tight anyway

                                                MichaelG.

                                                #242846
                                                Martin Kyte
                                                Participant
                                                  @martinkyte99762

                                                  My thinking Michael was that in operation the fork leg has to withstand the dive of the front end of the bike under heavy breaking which is probably going to be far greater than any shock force you could produce by whacking the end of the piston with a large hammer. If the bearings can be removed with the slide hammer method as manufacturers suggest then they don't need a great deal of force to shift them. Certainly less than the burst pressure of the fork leg. So the bearing is going to give in before the fork leg does. It's a moot point anyhow now we know about the slots in the bearings. I suggested the method because the means seemed to be at hand rather than making or buying a slide hammer.

                                                  regards Martin

                                                  Posted by Martin Kyte on 14/06/2016 11:35:23:

                                                  Why do you think that then Michael. Why should the leg burst before the bush moves. Do you actually think you can produce that amount of pressure?

                                                  Martin

                                                  .

                                                  32mm diameter piston, driven hard enough to move a bearing with such a small end-area [wall-thickness is only 1.5mm] suggests some pretty high fluid pressures.

                                                  Happy to be wrong; but I think a slide-hammer might be safer.

                                                  All depends on how tight the bearing is fitted into the bore of the leg.

                                                  MichaelG.

                                                  #242850
                                                  Michael Gilligan
                                                  Participant
                                                    @michaelgilligan61133
                                                    Posted by Martin Kyte on 15/06/2016 09:17:59:

                                                    It's a moot point anyhow now we know about the slots in the bearings.

                                                    .

                                                    Quite so, Martin yes

                                                    We've explored some options, which might be useful if anyone has a similar problem.

                                                    MichaelG.

                                                    #242861
                                                    Ian S C
                                                    Participant
                                                      @iansc

                                                      Is it a bush or is it a baked on Teflon coating? Ian S C

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