Nalon Viper

[Bill PudneyParticipant @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

[Graham Williams 11Participant @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.

[JasonBModerator @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

[Graham Williams 11Participant @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.

[Bill PudneyParticipant @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

[egaParticipant @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.

[Graham Williams 11Participant @grahamwilliams11]

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

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

[Graham Williams 11Participant @grahamwilliams11]

Picked 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.

[Ramon WilsonParticipant @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 run 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

[Graham Williams 11Participant @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

[Ramon WilsonParticipant @ramonwilson3]

Hi Graham – whilst I quite like machining cast iron for its machinability like you I do dislike the mess/dust it creates . 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 layoff

Regards – Tug

[Graham Williams 11Participant @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

[Ramon WilsonParticipant @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

Good luck with the rest of the build – Tug

[Bill PudneyParticipant @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

[Graham Williams 11Participant @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

[robjon44Participant @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

[John MCParticipant @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

[Ramon WilsonParticipant @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 though

Regards – Tug

[john feeneyParticipant @johnfeeney58965]

Hi,

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 Feeney

[Ramon WilsonParticipant @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

[Graham Williams 11Participant @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.

[JasonBModerator @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

[Ramon WilsonParticipant @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

[Graham Williams 11Participant @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

[Tim StevensParticipant @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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