NALON VIPER 2.5 CC DIESEL

[Roy VaughnParticipant @royvaughn26060]

Hi Tug. The contrapiston can sit anywhere in the bore so all that's needed is a longer comp screw, it wasn't an issue on my motor.

Re glow fuel, I'd be wary with the stuff in model shops nowadays, there are a lot of low/synthetic oil blends about which probably don't suit older motors. It's difficult to find out what's in them and how much of each ingredient.

Roy

[Ramon WilsonParticipant @ramonwilson3]

Hah! Now why didn't that occur to me!

I'd say that's a great case of lateral thinking Roy

I can't recall the last time I visited a model shop the local ones long gone. For many years I've only used fuel from the husband and wife team of 'Southern Modelcraft' in Kent. Unfortunately only available from them at shows they attend or at their premises they do not supply shops nor will send it by courier but the quality is superb with consistent performance.

Though they do do synthetic based (glow) fuel I only use their castor based 5% nitro for glow and their Sport and Hi-performance diesel. As previously mentioned elsewhere the diesel will keep for years in a tightly capped tin but the castor in glow fuel for some reason can degrade if allowed to get cold in storage. Apparently that can be put right by heating the fuel but I've not tried it to say positively.

My days of visiting shows have come to and end but fortunately I have squirrelled enough of both to see the rest of my (control line) flying days out – I hope!

What do you fly BTW

Best – Tug

[Roy VaughnParticipant @royvaughn26060]

Tug, going a bit off topic, I'll PM you, Roy

[Ramon WilsonParticipant @ramonwilson3]

Though I'm sure Keith wouldn't mind Roy I agree – will reply later, painting the shed at the mo

Tug

[Neil LickfoldParticipant @neillickfold44316]

A hard chromed liner can handle the oil content down to 12% castor with a cast iron piston. But the cast iron piston and steel sleeve, like the materials used in a PAW engine, the synthetic oil fuel will ruin the piston liner fit after about 6 or so flights. Castor oil is one of the few oils, that will allow oversized parts to assemble. It is also very good when assembling the contra pistons to liners or heads depending on the configuration. After running the engines, I recommend that the engines get flushed out with some kero or other similar solvent , and then oil with AFT oil or after run oil. The washing out is to get rid of the castor oil, as it is hydroscopic, and can cause the bearings to rust. Some never have issues with bearings, and others do.

I think the main reason for going to the smaller front bearing was to get the weight down, and to also make the front of the engine narrower for aircraft designs. I don't think there is a problem with the cars for the front bearing diameter, but I do like the different sized bearings, as it makes it easy to control the spacing. I once made some changes to a diesel F2C team race engine, and made a special shaft spacer, that locked the rear race inner to the flywheel and the spacer, and it locked the front inner race at the same time. It worked really well for what it was intended to do. The front bearing outer was retained with a small threaded ring.

It is always satisfying running an engine that you have made, and the more of it you make, the better it is.

[KEITH BEAUMONTParticipant @keithbeaumont45476]

Roy,

I am interested to know why you would want the piston to have a flat top.? With the 4 inlets angled up at 25 degrees,the piston top is the same angle,the purpose of which is to make sure that maximum fuel is forced to the top of the cylinder. The Mills 1.3 engine was advertised as having a notch in the piston top, adjacent to the inlet. to atomise the incoming fuel. This was claimed to be the reason for their famed easy starting.

Also, if you cut the top off the Vipers piston,as drawn, you end up with a big hole in it, as the inside shape follows the outside.

Keith.

[Ramon WilsonParticipant @ramonwilson3]

Re the Mills comment Keith,

 

I always thought that the piston was stepped to give the desired inlet  transfer timing as opposed to a technical improvement reason. Did they advertise that as a feature at the time? There were those series of adverts in Aeromodeller that consecutively described the Mills attributes but that doesn't ring a bell. Besides – if a Mills piston is fitted in the wrong way round it will fire on a prime but will not run.

Re Neil's comment on old castor in bearings – this was the inside of a Merco 61 I rebuilt a while back

Edited By Ramon Wilson on 06/09/2023 13:50:03 Inlet should have been transfer

Edited By Ramon Wilson on 06/09/2023 13:51:20

[KEITH BEAUMONTParticipant @keithbeaumont45476]

Hi Ramon,

Yes I have the Mills advert series. Attached is the one I mentioned.

Keith

[Ramon WilsonParticipant @ramonwilson3]

Well how about that Keith

I can't say I can remember that as I wouldn't see an Aeromodeller magazine until 1958 (age 13) but I did collect them back as far as 1944 and do remember the adverts generally.

I've looked at some other side port drawings some have a step in the piston on the transfer side others don't but as said if it isn't there by the piston being wrongly installed the timing is affected quite badly so was Mills making a thing of it as a sales pitch – after all why not do the same on all pistons at the point of transfer if it's that effective – who knows?

I've had quite a few Mills through my hands over the years all of which were accompanied by a 'Can't get it to run' comment. Some were simply worn and required new pistons but a high percentage of them all had the pistons in back to front.

Best – Tug

[KEITH BEAUMONTParticipant @keithbeaumont45476]

Tug,

I think at the time most people believed it. I made Ron Chernichs version a few years ago and did try out the test, as suggested and there was a deffinate look of fine atomisation.I did not reverse the piston to see if there was a difference tho. Why were so many with the piston wrong way round? As a teenager, I would take one to work and start it by holding it in one hand and flicking with the other, to demonstrate it's easy starting !

Keith.

[Roy VaughnParticipant @royvaughn26060]

It was a new flat top piston Keith, sorry I didn't make that clear. I can't remember exactly the thinking, maybe along the lines of, well, my PAW 2.5 Goodyear engines are very powerful and they've got flat topped pistons. Also, they are easier to make!

Neil, interesting observations about oil in PAWs. My experience is a little different. We went through a period of using 12% ML70 with satisfactory results until Tony Eifflaender advised that castor was quicker. I tried our Nelson fuel with 10% castor and he was indeed right. We carried on with this percentage with some success! All the piston-liner fits were pretty loose so that may have helped.

Roy

[KEITH BEAUMONTParticipant @keithbeaumont45476]

Tug,

Re- reading the Mills advert, it claims the "Mills Transfer System " is Patented, so perhaps this is why others did not use it. It might have been a bluff of course. If Michael ,our Patent expert is out there, perhaps he will know more of it?

Keith

[Ramon WilsonParticipant @ramonwilson3]

Hi Keith, it certainly features in the odd side port design of the times so who knows? Mills engines did start well for the best part so maybe it has some effect – very few diesels have stepped or baffled pistons though.

I'm going to be offline for a few days – back later though

Best Tug

[VersabossParticipant @versaboss]

I hope it's ok to continue this thread, albeit it is not (yet) about building a Viper. But my problem is that I could not find out how to get the plans. I somewhere saw that they are available at modelenginenews.org, and emailed enquiries@modelenginenews.org. But I think now that's a dead site, as I did not get a response. Directly on that site, there is only stuff from 2002 to 2013. Now I' at a loss. Can someone here tell me where these plans can be bought?

Regards,
Hans

[Roy VaughnParticipant @royvaughn26060]

There was a link on Adrian Duncan's page of engines for home construction but it no longer works for me. Maybe it will for you. If that fails, pm me and I'll forward my copy. Roy

https://adriansmodelaeroengines.com/catalog/main.php?cat_id=214

[Ramon WilsonParticipant @ramonwilson3]

Hans, as you have found the 'Model Engine News' site is no longer functional.

The plans are available somewhere as is the collection of plans from the 'Motor Boys'. I believe Ken Croft made these available from a free download but as to where to find them I cannot recall. Ken does visit on here so maybe he can re enlighten us if he reads this.

Like Roy I have the Viper plans and the others from the Motor Boys e book on file so happy to help if wanted

Best – Tug

[VersabossParticipant @versaboss]

Roy – I went to adriansmodelaeroengines.com, a very interesting place but no downloads to find there. The links give error messages, 403 forbidden. Unfortunately also no email address. I have a candidate here for the wotizit page.

I will send you a pm,

with many thanks
Hans

[VersabossParticipant @versaboss]

Ramon, thanks for your offer. It seems Roy can help me, and I think "the others from the Motor Boys e book" would be too much for me to digest. I'm lucky if I manage to finish that Viper, I think I'm in the same age range as you!

Kind regards
Hans

[Ramon WilsonParticipant @ramonwilson3]

Ha! You need say no more Hans, but you are welcome to come back if you change your mind.

Good luck with the Viper if you go ahead with it.

Best – Tug

[VersabossParticipant @versaboss]

All sorted now, thanks to Roy I have now the Viper plans. As I expected, studying these brought up a couple of questions. Certainly there will be more when the work really starts!
But for now what has come to my attention.

In sheet 1, crankcase: what does the expression 0.005" witness mean in practical machining terms?

In sheet 2, crankshaft: how can the counterweight be machined (in the form as drawn) when the crank pin is in the way? Or is the pin pressed in, but not shown as such?

In sheet 4, cylinder: how is it possible to drill a #33 hole (2.9 mm ) at an angle of 25 °? Might be possible with a 3 mm slot mill, but that would be too large then? Or using 2.5 mm and then opening out a bit?

I started to read through the couple of Viper threads, including the long one from 2019 (what the Google search brings up). I saw a building report from someone, but that ended just when the cylinder machining would becoming interesting. I can't find that thread atm, lost again a couple of hours in searching.

Kind regards,
Hans

[JasonBModerator @jasonb]

I think the 0.005 is just a very slight easing of the inner edge where the angled cut meets the top of the crankcase. If you really enlarge the PDF you can tell the difference between construction lines and dimension lines

It is easier with a pressed in pin but can be done with a long slender tool, I would use something with a more rounded end so you get a fillet in the internal corners and that also makes it easier to move the tool front to back cutting in both directions. The alternative is to hold the crankshaft vertically on a rotary table and mill the recess, again probably I'd use a cutter with 1mm corner radius 6mm OA dia should fit easy enough

Might need to grind down a cutter's sides and plunge with the cutting ends,

Edited By JasonB on 19/09/2023 14:54:45

Edited By JasonB on 19/09/2023 15:05:31

[KEITH BEAUMONTParticipant @keithbeaumont45476]

Hans,

Glad you are now OK for Drawings of the Viper. I have been on holiday so was unable to offer my set.

Sheet 2 , Crankshaft, I pressed in the pin before doing any lightening. I usally hold the shaft horizontaly in the chuck and use a radius cutter in the mill. Take horizontal cuts either side of pin and you then have a nice radius in the corner.

Sheet 4, cylinder. The small difference between # 33 and 3mm will not effect any performance, probably improve it. Another version of the cylinder has much larger transfer holes, The important thing is to ensure the top of the hole is correct in relation to the exhaust. I used a 3mm solid carbide slot drill .(see previous page) One tip is to use a sacrificial plug in the cylinder to prevent snatch on breakthrough.

If you have any other queries just ask. Please make sure you give the necessary clearances to the Ball races.

Keith.

[Roy VaughnParticipant @royvaughn26060]

Yes, I have seen a number of build threads or videos which suddenly jump from a rough machined liner and no piston to a running engine, missing out the most critical and interesting operations! I have never used a pressed-in pin, it always seemed a recipe for trouble due to the difficulty of getting the interference fit correct. Whether the fit matters depends on how much and how hard you intend to run it of course. Good luck with the project.

Roy

[Ramon WilsonParticipant @ramonwilson3]

Hi Hans, only just become aware of these latest posts.

Though I haven't made a Nalon Viper as such I have made several engines with very similar liners and virtually identical exhaust and transfer porting layout

I have described this quite fully on build threads on the Model Engine Maker site – search for ETA and Oliver Tiger.

I use a cross slide milling attachment to 'drill' the transfer holes – I use an undersized FC3 milling cutter (eg 2.5 for a 3mm final size) to begin the hole until I have a full flat bottom surface then spot and drill through with a 2.5 drill being very careful on breakthrough though if the liner is mounted on a sacrificial mandrel that's not an issue. Once the initial hole is done I open up using another FC3 cutter to open to size right through. Depending on the wall thickness and angle of approach you may have to grind some of the cutter away on the shank to get the depth required.

I use the corner of the exhaust flange as a reference point to establish where to start the hole but a faint line scribed around the liner in the correct vertical position using the lathe and picking up with a sharp pointer at the angle required will be good enough unless you are seeking absolute perfection with accuracy of transfer timing.

Hope that helps some more

Best – Tug

[Ramon WilsonParticipant @ramonwilson3]

I just found out that the search suggested will not be easy to find!

Here are the direct links to the build threads

ETA

Oliver

You'll have to scroll through but may find something of interest

Best – Tug

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