piston

This is probably a stupid question , Something has gone wrong on the steam engine I am making , the piston is going too far up the cylinder . am I right in thinking that the piston should not go past the cylinder ports ? otherwise it wouldn't be able to exhaust all the steam . My piston rod is a couple of mil too long but the piston seems much too high , mybe the crank throw is a bit too much . ,Dismantle again , again !!!!!!

regards

It can depend on the individual engine as some have a reasonable space between piston and cylinder end covers, others are very tight and need a notch in the end of the cylinder and/or the spigot of the cover.

Take the cylinder off and see how much gap there is at the other end of the stroke between piston and cover, adjust rod length so you get an even gap at both ends.

Hi Phillip,

Your thinking is correct. The piston should not go past the cylinder ports but without knowing the position of the ports or pistons, it is difficult to comment. (a drawing would help). To get the maximum efficiency out of the engine you should utilise as much of the cylinder travel as possible with a minimum of clearance at each end. (Some clearance is needed to allow for expansion and steam flow).

If your piston rod is only a couple of mm too long and the piston is not bottoming on the end cover, it would suggest that the ports are in the wrong position or needs a notch cut out as Jason suggested. As long as the piston still seals before the notch.

Paul.

Edited By Paul Lousick on 08/04/2018 10:52:49

the ports are cast in ( stuart turner no 1 ) I will investigate further

regards

The piston on the No1 should stop short of the cylinder ends by 1/16" this will leave 1/32" gap once the covers have been fitted as they have a 1/32" spigot.

So if your cast passages are more than 1/16" in I would suggest milling a small amount away so that they go right to the end. Or if it is just one end that is more than 1/16" do that. I also notch the spigot so it does not cover the passage.

While you are at it poke some fuse wire into the ports and passages as you often find core sand still in them.

Phillip,

Could it be that your piston rod is a shade too long? what is the clearance at the bottom of the stroke?

Regards

Lofty

if the piston stops short at the ends by 1/16 , that will cover the ports . When the piston stops short of the ports top and bottom , it only has 1 3/4 inch stroke , but crank gives 2 in stroke . Piston is correct size . If as said the piston should end 1/16 short then that is within my grasp if I shorten the piston rod a little . But I am still confused about ithe piston covering the ports ( sorry I am thick . I have made engine before and the worked ok . never really noticed if the ports were covered )

regards

Looking at the sectional drawing in teh No1 book they do show the ports covered but that is not ideal. We must have had this crop up before as I have a drawing that I did that shows the extra notch which I mentioned in my first reply which is shown below.

As per stuarts

Notch cut with a 1/4" cutter to width of cast port

Passage now reaches to end of cylinder but still leaves plenty of area for the cover to seal it

And how the piston will now leave the modified passage open when at the top and bottom of the stroke

that sounds like a scheme , I can do that OK , Then my piston will be OK . Thanks ever so , I was getting worried that had made a disaster , but I couldn't work out where . The must have been hundreds of No 1 s made to presumably they will work with the ports covered at the ends of the stroke , but must be better to be able to exhaust all the steam

regards

no of course ,I remember that the previous engines I have made have had the ports drilled from the ends so they would be uncovered

regards