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  • #433900
    Bill Pudney
    Participant
      @billpudney37759

      Both of mine used a machined from the solid crankpin. They were finished as well as I could do. Finished up with a "poor mans ground finish"….emery sticks and oil!! To use a pressed in needle roller would be somewhat better from a performance point of view, but there are technical issues, the crankweb needs to be a lot thicker, I've heard a minimum of 1.2 times the pin diameter, to ensure that the pin is well supported. However, some of my commercial modern highish performance 2.5cc motors use a 4.0mm diameter crankpin, which would "only" require a 4.8 or 5.0mm thick web. Theoretically. Then you have to answer the question "….Is this a Nalon Viper??" !!

      Chrome plating various bits would be very nice, but introduces yet another layer of complexity as any plating would need grinding or at least honing/lapping.

      You are spot on about the mess that cast iron makes, I recently finished a carriage and compound slide for a small (70mm centre height) lathe. This required a lot of machining, although I cleaned up after every session, (sometimes after every cut!), and took care with chip shields etc, the cast iron dust got everywhere.

      best of luck!

      cheers

      Bill

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      #435049
      Graham Williams 11
      Participant
        @grahamwilliams11

        progress so far on the engine. been searching for 6ba cylinder holdown studs but nothing at length needed (1 3/4&quot so most likely use 3mm.

        img_20191028_131430024.jpg

        #435050
        JasonB
        Moderator
          @jasonb

          Looking good.

          I doubt you will find ready made studs to suit but the likes of EKP sell 7/64" steel which will take a 6BA thread nicely if you don't want to go up to M3

          #435062
          Graham Williams 11
          Participant
            @grahamwilliams11

            Used the wrong term they're not studs, drg showing cap screws to hold down the cylinder etc so might now go to 6BA cheese head bolts/screws as nothing else comes up in searching for the needed length.

            #435119
            Bill Pudney
            Participant
              @billpudney37759

              I was able to get 6BA socket head screws from GWR Fasteners, at least for the bearing housing and backplates. They no longer list the longer (1.25"??) cylinder retaining screws, afraid I cannot remember where I got mine. I've just had a look at the engines and mine are definitely 6BA SHCS.

              cheers

              Bill

              #435138
              ega
              Participant
                @ega
                Posted by Michael Gilligan on 17/10/2019 08:44:09:

                Wikipedia has quite a good page about Duralumin and related alloys.

                MichaelG.

                .

                Edited for clarity … I hope.

                Edited By Michael Gilligan on 17/10/2019 09:11:45

                There is also an interesting Wiki about Hiduminium, another proprietary name. My first proper bike had brakes made of this.

                #435188
                Graham Williams 11
                Participant
                  @grahamwilliams11

                  Finish turning the crankshaft up today then rear housing next, doing the less difficult bits first.

                  img_20191021_133443623.jpg

                  Edited By Graham Williams 11 on 29/10/2019 18:44:00

                  #441267
                  Graham Williams 11
                  Participant
                    @grahamwilliams11

                    img_20191205_181415751.jpgPicked up again after doing some work on my Velocette. Made the rotor, backplate and needle valve and the liner. Made the first liner from what I thought was EN1 but was tougher to machine so made another from known EN1A which machined more easily, also machined it in a slightly different order, both turned out OK, left the bore 1 1/2 thou undersize ready for lapping. Plans show cast iron for the liner but advice was to use mild steel which I must prefer as it's not dirty to machine though the pistons will have to be cast iron, Will need to source a 'tired' mini lathe to do the lapping in as I've decided not to use the Myford for that job.

                    img_20191211_150107875.jpg

                    #441449
                    Ramon Wilson
                    Participant
                      @ramonwilson3

                      Hi Graham, did reply to this late last night but went back a page without copying and lost it all!

                      It's looking good – not long now before that first runyes I think you'll find that the washers under the capheads aren't really necessary though – I don't ever recall any engine using them.

                      Sourcing long 6BA SHCS could prove an issue but cheese heads would be fine – again that's what virtually all similar sized engines of the period used but even there you may find it a problem. I have similar issues with 5BA so turn mine from 6mm En1a. I put a small centre in the end for support and make the thread longer than required turning the centre off and reducing to the correct length after.

                      'Cast in cast' is okay from a piston/liner combination of metals point of view but it does make for some messy exhaust residue. The initial seal usually reduces a little before the surfaces beds in too. I have just rebuilt a 5cc Miles Special for a friend which had a cast liner and piston. Relapped the liner and made a new piston. Once run that initial compression eased a tad though the seal is still good. Personally – for a basic home built I would not move away from a cast piston in an En1a Liner – a good combination of metals with exccellent abillity to create a very good piston/liner seal.

                      I don't think you have too much to fear about using your Myford for lapping if you ensure the bedways are well covered and the saddle pushed well back out of the way. Never seen that as an issue on mine on this op.

                      Looking forwards to seeing it run

                      Hope it all goes as well as it has to date

                       

                      Regards – Tug

                      Edited By Ramon Wilson on 13/12/2019 11:46:45

                      #441465
                      Graham Williams 11
                      Participant
                        @grahamwilliams11

                        Hello Tug. You're right about the washers, they do look somewhat awkward so will dispense with those in due course. Have some 3mm cap screws but haven't tapped the c/case as they look clumsy as well so just ordered up some 2" long steel cheese head in 6BA so will shorten those and use them instead as you suggest. Bill Pudney in OZ suggested the EN1A/cast combination which appealed to me more as, you've probably guessed, I don't like machining cast iron . As to using the Myford for lapping, a very experienced flyer/engine reconditioner on the Barton site, who lives not far from me, kindly showed me his approach to liner/piston fits, he kept the lapping separate to his lathe, a Myford copy, using an old Hobbymat, which obviated the need to have lapping medium near his main machine. If I can get a tired mini lathe, which isn't proving easy, as all on offer seemed to be described as pristine!!!!! I'll set up for doing it that way as I've picked up some worn engines at boot sales again as well, otherwise I'll have to bite the bullet and cover everything in clingfilm and use the Myford

                        Fingers crossed it'll run, if it's ok have enough material to build a second one, (using the other liner) and it should be quicker as I now have a number of fixtures to machine the various parts lol.

                        Regards

                        Graham W

                        #441475
                        Ramon Wilson
                        Participant
                          @ramonwilson3

                          Hi Graham – whilst I quite like machining cast iron for its machinability like you I do dislike the mess/dust it creates sad. I have rigged up a vaccuum system on the mill but not on the lathe. Have to wear a mask too now as the dust really gets to me

                          Though there are several very knowlegeable memebers on there to chose from if, by 'experienced flyer on the Barton site', you possibly mean Johnny Alcock then you really couldn't have a better mentor. If it is then please give him my regards.

                          My use of cast in steel appraoch to piston/liner came from an article by George Aldrich in SIC some years back.

                          I was given a couple of old control liners yesterday with a well worn PAW 19 in one and a nice condition externally but somewhat lacking in compression AM25 in the other. Like you I have some rebuilding on the cards – I have started C/L flying again after some thirteen years layoffsmiley

                          Regards – Tug

                          #441482
                          Graham Williams 11
                          Participant
                            @grahamwilliams11

                            Hello Tug. Like you it's the dust off cast iron that gets on my chest no matter what mask I seem to use, might have to go the NBC route lol. You got the guy in one, a thoroughly nice bloke, willing to help in any way he can, one thing he did say which hit home was that it's not easy to get the fit at first, success rate he said was 1 in 10 when he started many moons ago and perseverance is the name of the game until you finally get what's needed, Seems AM25 are in abundance as I now have 3 to re-bore and 2 NVAs to make. Started on the Nalon piston, inside and outside turned and set up to cross drill for the wrist pin, but can feel the dust already so switched to polishing the Velo for a while. LoL.

                            Cheers

                            Graham W

                            #441552
                            Ramon Wilson
                            Participant
                              @ramonwilson3

                              Well you are definitely in good hands there Graham, there's little that Johnny doesn't know on engines and flying control line – as you say a real great guy and always willng to help.

                              As he's said, getting the fit right is the make or break of the project so take your time – when that breaks into a run you'll really be grinning from ear to ear smiley

                              Good luck with the rest of the build – Tug

                              #441560
                              Bill Pudney
                              Participant
                                @billpudney37759

                                I've just had a look at my motors and the cylinder holding down screws are 1.25" long, not 1.75" as stated on my set of drawings. This may make the cap head screws easier to obtain!!.

                                Also, a couple of weekends ago I started the running in process on #1, it had been delayed by other stuff. It goes very well!! Starts easily, fairly smooth, turns a 9" x 4" Taipan at about 11,400 rpm which is pretty good. There are a few issues with the needle valve assembly, so there have been further delays whilst I try and put that right!!

                                I'm envious that you have a Velo to polish!! One of my favourite bikes!!

                                All the best

                                Bill

                                #441565
                                Graham Williams 11
                                Participant
                                  @grahamwilliams11

                                  Hello Bill. Made up a bill of materials for the engine and sourced from that, as you say the drgs are saying 1.75" so will have to search again for the correct length cap screws or stick with cheese head if unobtainable.

                                  Oz was a good market for Velos and there's a thriving club, only got one Velo left now, foolishly I sold the other 5 some time ago when space became a problem, which was a big mistake, should have extended the garage, foresight valuable, hindsight not……. o well.

                                  Made my needle valve standard with cross drilled 1mm holes as that's how I've made them before but if that doesn't pan out will make as per drg, which at least means there's no need to grind a taper on the needle.

                                  Cheers

                                  Graham W

                                  #441604
                                  robjon44
                                  Participant
                                    @robjon44

                                    Hi Ramon, it is recognised that anyone can become increasingly sensitised to cast iron dust, in times gone by a condition called Turners Lung was recognised by doctors, I have only ever known one person in a lifetime as a turner who had it whilst working manual lathes machining shedloads of CI dry & he said he was coughing up rust !, however he eventually got a job with a reputable company with a more enlightened view of H&S more creative filtration etc. In more modern times on CNC lathes the size of Transit vans we always machined it under high pressure coolant without problems.

                                    I suggest as a solution acquiring or making one of those belt packs worn by welders which supply filtered air into their helmets which protect them from the noxious products of their welding activities, all of my mates who were welders swore by (not at) them.

                                    Bob H

                                    #441682
                                    John MC
                                    Participant
                                      @johnmc39344

                                      I've just had a look at the drawings of this engine. I think there is a problem with the way the crankshaft bearings are mounted. When the engine gets hot the aluminium bearing housing will expand approximately twice that of the steel crankshaft, therefore putting additional load on the bearings.

                                      I've looked at a few engine drawings of this type of engine and there seems to be a common theme of incorrectly mounted rolling element bearings.

                                      Unfortunately incorrect rolling bearing mounting isn't confined to these small aero engines, there are have been many designs in our "world" that have ignored the principals. In industry the principals are well very well known but sometimes ignored. A good example is bicycles.

                                      Definitely a need for some one to write about this in one of our magazines.

                                      John

                                      #441690
                                      Ramon Wilson
                                      Participant
                                        @ramonwilson3

                                        Hello Rob – Thanks for your thoughtful input. Fortunately I don't suffer with any lung problems but do notice the effect that the dust from cast iron creates – that also goes for balsa dust at the other end of the spectrum too so use a mask for most dust creating operations these days

                                        John MC – John, I'm afraid I don't see the problem as you see it. This engine design has the same bearing set up as countless others of the same make up. As the engine gets hot of course the case indeed expands but it doesn't expand inwards to create as you imply an additional load on the bearings – if anything, if the initial bearing fit is of a low order the bearing can loosen in the case.

                                        The person who designed this engine initially was a well known designer at the time and it was redrawn by another well respected person in the model engine world – all I can add is that if your observations are correct so many many manufacturers have got this wrong over many years.

                                        I perhaps should add however that my thoughts on this are based purely on practical experience and not on any specific in depth technical knowledge of bearing application per se.

                                        Nice to see some input on the subject of these small engines thoughsmiley

                                        Regards – Tug

                                        #441698
                                        john feeney
                                        Participant
                                          @johnfeeney58965

                                          aeromodelling-model engine 2013 022 (small).jpgaeromodelling-model engine 2013 018 (small).jpgHi,

                                          This is not a problem in practice. For the engines I make I bore the bearing housing about 0.001" under size, this for bearing of 19 or 22 mm outside diameter. These engines run at 16000 to 20000 rpm. There are other ways that have been used such as fitting a steel sleeve into the aluminium crankcase but even in very high performance engines the direct fitting into the aluminium is usual. There are many other aspects regarding fits in small engines which run at high speed and use only the oil in the fuel for lubrication.

                                          John Feeneyaeromodelling-model engine 2013 016 (small).jpg

                                          #441710
                                          Ramon Wilson
                                          Participant
                                            @ramonwilson3

                                            Sorry to impinge on your thread Graham but John thats a very nice looking engine there – is that your own design and likewise the castings?

                                            Love the black finish – is it destined for any specific aeromodelling use FF or TR perhaps

                                            I've always preferred rear intake motors, don't know if you are aware but have now made several 5cc versions of early well known smaller engines.

                                            Due to lack of suitable measuring kit I usually turn and polish to a high finish a plug guage for the bearing housing. I make this 0.02mm down on desired diameter on 24/26 diameter bearings. When that just slips in the cavity the fit is just about right though may need a slight tweaking with a piece of 800 wet and dry paper if a little tight on the bearing.

                                            Tug

                                            #441712
                                            Graham Williams 11
                                            Participant
                                              @grahamwilliams11

                                              Can only agree Tug, they do look very nice indeed, slightly green with envy as never have taken anything other than one of my bikes to that level of finish, sort of old East German functionality not Victorian splendour is how things end up for me. As to bearing fit I go with how a lot of bike bearings in gearboxes and in crankcases are usually fitted, undersize by 1.1/2thou ish, warm the casting and chill the bearing and drop them in, hope it works on this engine, we'll see.

                                              Cheers

                                              Graham W.

                                              #441719
                                              JasonB
                                              Moderator
                                                @jasonb

                                                John MC, you mentioned this before in another thread where you were commenting on axial location, from my limited use of model aero and buggy engines there is usually some end float in the crankshaft so no risk of things tightening up and adding load if the crankcase expands length ways with heat.

                                                I've a little OS 20 that is almost unused in my hand right now and that must have 0.020" endfloat.

                                                Edited By JasonB on 15/12/2019 13:21:19

                                                #441736
                                                Ramon Wilson
                                                Participant
                                                  @ramonwilson3

                                                  Graham – you might find 1 1/2 thou a little on the tight size on the bearing size required. I would have thought just under a thou would be fine. I usually fit the bearing to the crankshaft first then heat the case with a hot air gun nice and hot then drop the shaft in. The bearing should just drop in place in one movement. Once cooled if the bearing feels tight on the shaft then it's removed and the housing opened very slightly with wet and dry paper – a bit unscientific but always had good results so far.

                                                  Tug

                                                  #441747
                                                  Graham Williams 11
                                                  Participant
                                                    @grahamwilliams11

                                                    OK Tug, thanks once again. Will measure up again when I'm back in the W/Shop tomorrow and bring it to less than a thou under bearings od. and go from there.

                                                    Cheers

                                                    Graham W

                                                    #441772
                                                    Tim Stevens
                                                    Participant
                                                      @timstevens64731

                                                      A bearing housing will expand when hot – outwards – and exactly as much as it would if it were solid metal. As it does so, the steel bearing (or shaft) becomes a looser fit in the aluminium, and this means that the area of contact reduces slightly. So slightly, I suggest, that the effect of heat and the stesses from torque and combustion on all the other bits make the effect of minor importance. It is not, afterall, as though your model is going to be required to fly the Atlantic non-stop, is it?

                                                      Cheers, Tim

                                                      Edited By Tim Stevens on 15/12/2019 17:45:38

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