4 cylinder rotary valve

[astroud]

This is my own design which I have been building for the last few months. It is a bit of scrap box special, hence the cylinders made from 22mm copper pipe. The crankshaft runs on skateboard 8mm ball races and has a centre plain bearing.
I am planning a single rotary valve driven at half speed by a timing belt, going to mock it first before  cutting metal to make sure of the concept. One concern is that there will be too much friction from the shaft and belt drive for the engine to overcome, we shall see.

Andrew

[Sanjay F]

Fantastic Andrew - you have made great progress, I look forward to following this interesting build 

[PaulR]

Great stuff Andrew, looking forward to seeing how this works out!

I take it the copper pipe needed a bit of a skim on the inside? What material did you use for pistons? Will it be run on air only?

I've been thinking about a multi-cylinder rotary valve engine for some time, my idea was to bore cylinders in a single block of brass but it starts getting pricey for experimentation. I've only tried turning copper a couple of times (for boiler end plates) and it wasn't much fun as I recall.

PS I'm also building a very simple wobbler to use up some brass scrap - I spend yesterday's session sawing up and plugging holes in two chunks of brass from previous engines that had gone wrong.

[55fairlane]

Watching with interest

[astroud]

Hi Paul
I did not attempt to skim the pipe id , as far as I could tell the diameter is consistent and the surface finish is good. The only machining I did was to face off the ends to reduce the slight lip caused by cutting with a plumber's cutting wheel and to get the finished length. Drama free with very light cuts. I reckon trying to skim the id was likely to end up with grief.
The pistons are made from aluminum so soft on soft, a poor combination but material was in stock and easy to machine. No particular clearance, just the best fit I could get. I put in a single oil groove to help with sealing and lube. As assembled it turns over quite freely.
It will run (if it runs) on air only.
Brass is lovely to machine but pricey, glad you can reuse some scrap. You can get thin wall tube which I have used in other models as a cylinder liner allowing me to use a mild steel block with a rough machined bore. Good luck with your wobbler I admire your models and your desire to do something different.

Andrew

[PaulR]

Hi Paul
I did not attempt to skim the pipe id , as far as I could tell the diameter is consistent and the surface finish is good. The only machining I did was to face off the ends to reduce the slight lip caused by cutting with a plumber's cutting wheel and to get the finished length. Drama free with very light cuts. I reckon trying to skim the id was likely to end up with grief.

You've inspired me to have a good look at some copper pipe later! I've also got lots of some sort of 'brass' tube I've been hanging on to but I think from memory it has a seam so might not be much use.

Nicely machined pistons you have there 

[astroud]

Hi all
Good progress, I am nearly ready to make the first run.
After much sketching and experimenting with a wooden dowel and carboard tube I have cut the rotary valve. I was very nervous about getting the correct slot orientation for the direction of rotation and the 'firing' order. The hole for the rotary valve was drilled, quite the roughest hole I have made in a long time, brand new long series drill and plenty of lube so I don't know why it is so rough. Fortunately it is straight and a very good fit for the valve.  I convinced myself the grooves left by the drill in the hole would act as a labyrinth , holding oil and sealing.
I wanted to avoid the complications of a timing belt tensioner so the centres were carefully calculated and finely adjusted with paper gaskets on the top of the copper cylinders where they fit in the head. I have fantasised about variable valve timing and  some stage I might fit a longer belt and a tensioner so I can try variations in the relative position of the 2 pullies. The pullies are ebay items and I will probably narrow them down to suit the 2mm wide belt.
The screws on the top of the head are oiling points, and I have yet to make some short exhaust pipes.

Andrew

[astroud]

second photo

[PaulR]

Great! Looking forward to seeing and hearing this running!

"I convinced myself the grooves left by the drill in the hole would act as a labyrinth , holding oil and sealing. "
  I'll remember that and probably have cause to use it often!

[AlexS]

Looking great. Otherwise running the engine with dc motor on a desk is also interesting!

[astroud]

I am happy to say the engine is a runner, and I am very happy with the result. Using copper pipe for the cylinders and a belt drive for the valve opens up other possibilities, I think a V would look quite handsome.

<a href="https://www.youtube.com/watch?v=tbSeEa-HI6c" target="_blank">http://www.youtube.com/watch?v=tbSeEa-HI6c</a>

[PaulR]

Excellent, seems like a really solid runner and quite a different sound to it 

[Sanjay F]

Well done on designing and creating a running engine, it must be very satisfying!