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Nalon Viper

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Graham Williams 1118/10/2019 07:04:10
28 forum posts
9 photos

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.


Graham W

Bill Pudney18/10/2019 07:28:17
424 forum posts
16 photos

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!!



Graham Williams 1118/10/2019 09:48:01
28 forum posts
9 photos

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' .


Graham W.

Ramon Wilson18/10/2019 10:58:45
676 forum posts
72 photos

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

Bill Pudney19/10/2019 01:57:49
424 forum posts
16 photos

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!



Graham Williams 1128/10/2019 15:09:15
28 forum posts
9 photos

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.


JasonB28/10/2019 15:23:28
16446 forum posts
1739 photos
1 articles

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 1128/10/2019 16:36:31
28 forum posts
9 photos

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 Pudney29/10/2019 02:02:54
424 forum posts
16 photos

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.



ega29/10/2019 10:05:51
1290 forum posts
109 photos
Posted by Michael Gilligan on 17/10/2019 08:44:09:

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



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 1129/10/2019 18:16:25
28 forum posts
9 photos

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

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