Nalon Viper

Hello Tug. Been an admirer of your work for ages, I'm sure your Viper will be superb as all the others. 6082 is what I'm using now it does machine nicely so with the views posted here I'm sure that it'll work out ok. Not destined for a model it's just an excercise to keep me active since I retired, refurbed a few engines and made a BollAero which is now running and when I saw the plans for the Nalon reminded me of the Mk 1 ETA15d I used in FAI power models in my younger days. If it runs then I'll be happy though usually to get the fit of the liner/piston/contra correct it takes a few goes, still learning about the lapping process though I've had some excellent advice and a demo on the methods used from a really knowledgeable guy who lives quite close to me. We'll see how it goes and if it's a success will move on to another one that takes my fancy from the MB book.

Cheers

Graham W

I made a couple of Nalon Vipers a year or so ago, there is a photo of my Mk1 in an album. I used 6061 T651 for the front bearing housing, fins and rear backplate, 2014 T3 for the crankcase, 4140 steel for the crankshaft, meehanite for the pistons, 12S14 (similar to leaded EN1a) for the liner, 2024 T3 for the conrod, delrin for the rotary disc. Please forgive the furrin material specs, but I'm in Australia and most of our metal comes in American specs.

Incidentally 2024 T4 or better is usually recommended for conrods, and it is certainly very good, but it's also expensive, I once was quoted US$40 for a 24" length of 1/2" diameter bar which I found (just) acceptable, but it was US$120 postage from America!! The reason that 2024 is often stated as the preferred material was because of its better properties at elevated temperatures. So I investigated and proved to my satisfaction that 7075 T651 was ALMOST as good, except for a tiny drop at fairly high temperatures, around 200 degrees C if I remember. The big advantage was that my local supplier could supply 1/2" bar at about AUS$20 a meter!!

best of luck!!

cheers

Bill

Bill. As you've made a couple of Vipers could I ask whether you used a press in crank pin or machined it from the solid, also Ron Chernich's description gives a hard chromed, presumably press fitted, crank pin size of 7/32" dia but the drawings I have show 3/16" dia.and con rod to suit. Also you've used EN1A equivalent for the liner, I was going to follow the drawings which show cast iron but it's a dirty metal, and steel would be better from the point of view of keeping my lathe 'cleaner' .

Cheers

Graham W.

Hi Graham,

Thanks for your compliment - appreciated.

Your approach is very much as my own in that mine are just ME projects though having recently returned to C/L flying I do have intentions of fitting at least one of them to a model in due course.

With regards to liner material I have only done one from cast and one from a very tough steel. Cast is fine of course and makes for ease of machining but does make for not only the mess on the lathe but for a very messy exhaust residue for quite some time. After I read an article on using leaded steel for liners with cast pistons things much improved both from a lapping process and piston/liner fit. All subsequent engines have been done as such and compression is very acceptable. The wear properties of En1a in cast is very good so I don't harden anything though another engine builder Dick Roberts told me he case hardens his En1a liners by filling the liner with Kasenite and heating thouroughly. Personally, though he assured me he had not experienced it, I would not risk the potential for distortion. I don't know if you've seen any of the build logs I posted on Model Engine Maker but if not that might be worth a look as this subject is covered in depth.

I have only ever fitted one press fitted crankpin - an Eta15d converted to the Stockton/Jehlik specs. This was for Mike Crossman and destined for a T/R - I've never heard anything on how well it performed so can't comment but I do know someone who fits all his 3.5cc engines for use in combat flying with crankpins made from needle roller bearing rollers with great success. All the crankshafts in the 5cc versions have been made from En24T with the pin turned as part of the web.

Bill's comment on the 7075 is warranted - I use a material called Alumec 89 but supplies are very limited now as my source has retired! It came from a local factory and was off cuts from material used for making moulds for blow moulding. A very tough ali which has stood up to the task well.

I'll look forwards to seeing yours run - I still get a buzz from firing one of mine up. In the meantime if I can be of help I'll be glad to.

Regards - Tug

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

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

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

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.

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

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

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

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.

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

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

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

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

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

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

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

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