NALON VIPER 2.5 CC DIESEL

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

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

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

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

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

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.

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

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

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