scratch built beam engine

Hi all

Just finished my scratch built beam engine , and am having trouble trying to get it to turn over on air. At present the air is entering the valve chamber and coming straight out of the exhaust port. My valve is floating on its spindle and the air seems to be leaking between the valve and the port face. I assumed that the air pressure in the chamber was supposed to keep the valve firmly seated, have I got this wrong.

This is why people lap the port face and valve flat. If the faces are good are the edges of the nut on the spindle and the sides of the valve they drive at 90 degrees to the axis of the spindle?

Yes pressure should hold it on. Do make sure that the nut has not been tapped wonky as it can prevent the valve sitting flat on the port face and that the valve is not fouling the valve rod.

If it is just a bit sticky try tipping the engine over so the port face is flat and valve will be helped by gravity until it all beds in.

Many thanks for replies. I tried tipping the engine up so gravity was pulling the valve down, but although the piston tried to move a little there is still to much air escaping for it to work. I will take the valve chest of tomorrow and try to lap the valve down so that it makes better contact, and check there is nothing in the way stopping it from laying flat.

Cheers Mike

Hi Mike, before taking anything apart, you might try a good splash of thick-ish oil down the steam or exhaust pipe to wet the valve workings. The oil may help it seal, if everything else is OK.

Decided to take it apart tonight. After very careful inspection I think I have found the problem. On one side of the valve chamber at the bottom there was a very tiny ridge of metal running the whole length, I only found it by using a magnifying glass. The valve was running on this instead of the bottom. I have now removed this and re-polished the chamber. Hopefully when I rebuild it tomorrow it will work. Will keep you posted.

Mike

Athough not an interferance fit the valve needs to be held close to the port face or air will get under it and it will never seat. Its also possible your timing is out so instead of going to compress the cylinder it is going straight out the exhaust - thick oil is always useful for starting out.

I would be very interested to see photos and diagrams of your beam engine if you have any.

Spent this afternoon refitting air chamber and testing engine. Happy to report engine now works very well , will run on just two pounds of air. I have enclosed a few shots so you get the general picture. This beam engine was built with the help of Stuart drawings , but I have scaled mine up from the Stuart version by about 60 %. Now I have a working engine I am going to finishing it of by adding a central fluted column plus various other upgrades. Many thanks for your help. Mike