NSU Cam Drive

[dvbydt]

I need a compact cam drive system for my compressed air V8 engine see:-

http://www.homemodelenginemachinist.com/index.php?topic=14530.0

I had seen this system in a review of a NSU Prinz car years ago and
filed it away to look at later, because I didn't understand how it
worked. The journalists that reviewed it didn't understand either so
just described it as "Two eccentric rods"


http://cybermotorcycle.com/gallery/nsu/NSU_Ultramax_Camshaft_Drive.htm

This is an animated version :-

http://www.nsu4.nl/english/e1ultramaxcamshaftsystem.html

The third rod nearest the engine just maintains the centre distance.

So, this how I have managed to explain it to myself, if it helps
anyone else, that would be a bonus.

Firstly, locomotive wheels are phased 90 degrees on each side, it is
called quartering and allows the double acting cylinders to be self
starting. ( Pretty useful, wouldn't want to push a steam train!)

Lego model so that both sides can be seen, not easy with a full
size engine.

http://www.youtube.com/watch?v=B78NleuC0oc&feature=youtu.be


Note that only the left side is driven. The right hand side is
made to rotate by the coupling rods.

Now I have transferred one of the rods to the other side :-

[ame]http://www.youtube.com/watch?v=nN_NtI8Bblg&feature=related[/ame]

Another view :-

http://www.youtube.com/watch?v=E5urzJWLE0U&feature=youtu.be

Again only the left side is driven.

If I can manage to machine the two 90 degree cams, I should have
a slick way of joining the crankshaft to the overhead cam without
the use of gears,belts or chains.


Ian

 

[cba]

Hi Jan, I had two NSU Max bikes (250cc single cylinder) long time ago. Unlike the frame, the engines were well ahead of times. A joy to take apart and reassemble (I was just 17 Years old then...). Like on your link, there were two long rods, made from aluminium with bronze bushings for the excenters. The third rod was indeed used to compensate for expansion. What you do not see on the sketches in your links, is that the cam could swivel along with the rocker arms inside a separate frame in the cylinder head - guided by this third rod. This was necessary to compensate for heat expansion of these long rods (by memory these rods were about elbow length or 35-40cm long), and heat expansion would have locked up this drive without this elaborate compenation mechanism). Cam and rocker arms had to swivel together, to ensure the valve play remained unchanged, the swivel axis had to be exactly at the tip of the valves. The valve springs were of the hairpin type, and lubrication was dry sump. I guess this engine was way too expensive to manufacture back in 1955, too complex for the only 18HP it had, but it functioned well and had a great ;D sound.

I think for a model, heat expansion should not be a problem and you can leave the third rod away. Chris

 

[raggle]

My heart leapt a little when I saw this post. I had almost negotiated the purchase of a 4 year old NSU Max in 1961 when my father died suddenly so I didn't proceed.

Then in the late 1970s I found a Prinz car which the owner told me was free for the taking - but with no documents. I drove it to my workshop several miles from home intending to salvage the power unit. This was 600cc using the same camshaft drive as the 250. It also had the Siba Dynastart on the crank. Might have suited a bike or sidecar oufit very well.

It was not to be - the workshop was rather full of work at the time and the landlord insisted on a clearout of the yard and I lost the thing to the scrappy :-[

What is it with me and NSUs?

However I gather that the 18 bhp (a quite creditable 76 bhp per litre in the '50s) was increased to 29 bhp @ 9,500 rpm for the Sportmax.

http://www.motorcyclespecs.co.za/model/Classic%20Racers/nsu_sportmax_250.htm

So the system certainly has legs. Go for it, I'll be watching!

Ray

 

[dvbydt]

Thanks for taking an interest, I will keep this thread updated with any progress. I am just trying to decide if I should make my test engine into a single overhead cam system to sort out the practicalities.

Ian

 

[dvbydt]

Well, it is possible to scale down this cam drive system.

[ame]http://youtu.be/Z4vHcDu1XfU[/ame]

The centre distance on this video is 40 mm and it is here driven by my battery drill, maximum speed shown is about 900 rpm. Using my mains drill, it will run up to 3,000 rpm easily. So it now needs some design work to get it to fit on the end of the crankshaft. In this application it does not need a gear reduction.

More details on my Compressed Air V8 thread.


Ian