Wolfie

A quick start is to set the valve gear at 90 deg to piston i.e. when the piston is at one end of the cylinder, top or bottom dead centre, the valve gear is mid travel. Depending on the which is used will determine the direction of rotation for your engine. Fine tuning of the valve timing will then be required to get the best out of the engine, others on this site are far better qualified than me to advise you on this.

The quick set above should get you going.

Cheers

Martin

Hi Wolfie,

90 degrees is rarely ideal not just beacuse you want some 'advance' or 'lead', but also because the valve may be designed with 'lap' – this means that it's not at 90-degrees that the valve starts to open and shut, i.e. the valve opens for less than half a rotation each way. This means you may need to rotate the eccentric further forwards by much more than 10 degrees to get some lead.

Why have lap? So that the valve 'cuts off' and only lets steam in for the first part of the stroke, and after the valve closes it works expansively. This makes the engine slightly less powerful, but much more efficient. the idea was worked out by Jonathan Hornblower, and Watt and his followers worked hard for many years trying to bury the fact that Watt didn't think of it first.

For example, a vlave might only let in steam over 150 degrees of its rotation at each end, so to let steam in at TDC the eccentric needs to be set 15 degrees ahead of the crank – (180-150)/2. But you need some lead, say 10 degrees for the reasons Jason explains, so the net advance of the eccentric might be 15+10=25 degrees (Pay attention at the back!)

That means the valve cuts off at 25+15=40 degrees before bottom dead centre, allowing teh steam to expand and make full use of its energy.

Compressed air doesn't do this as it has little energy to give up in this way, which is why steam engines run better on air.

I noted that Morgen's compound engine uses eccentrics at 90-degrees – and also that he runs his enginbes in air, so this makes sense. However a compound on low pressure air is possibly pumping the air through the LP cylinder rather than extracting energy from it and may run better on the HP cylinder only

Hmm,. Sorry if that goes on a bit, I've probably made an error in there!

Neil

Due ackowledgement to Tom Walshaw for cultivating my shaky understanding of this topic.

Hi There

Must have removed it then.

That is where I downloaded it a couple of months ago.

I only downloaded it for a reader, I must have deleted it afterwards.

It might be on a back up somewhere.

regards David

Hi Wolfie,

I don't know if this is of any help but these are the valve setting instructions for the Stuiart Beam engine from the instructions by Andrew Smith, They appear to be pretty generic so may give you a start for initial setting, Quote:

"……………Assembly complete, but leave the steamchest cover off until we set the valve, To do this, turn over the flywheel in the direction in which it is intended that the engine should run and watch the valve slide up and down across the port face of the cylinder. Adjust the valve by taking out the spindle (31) and screwing the valve rod up or down, until the valve opens the steam ports at top and bottom of the cylinder by, as near as possible, the same amount.

When this is done, undo the grubscrew locking the eccentric sheave to the crankshaft. Now turn over the crankshaft in the direction of rotation until the piston is exactly at the bottom dead centre, i.e. at the bottom of its stroke; now, with the crankshaft stationary, turn the eccentric sheave, still in the direction of rotation, until the valve reaches the bottom of its stroke and begins to rise again. Watch it carefully and as soon as it starts to uncover the lower port, stop turning the sheave and lock its grub screw.

Now revolve the flywheel and see what the conditions are like at the top of the piston travel. The valve should have risen to its highest position and started to descend uncovering the top port by the same amount as the bottom one when the piston had reached top dead centre. If it is not so. slacken the eccentric sheave grub screw and slightly rotate the sheave to split the difference between the top and bottom ports."

Hope that is of some help,

Regards

Terry

And if you really want to get into it, check out this:

**LINK**

I agree the the point made earlier that 90 degrees is not a good setting for eccentrics, and most need a lot more than 10 degrees or so of advance.

Joey

It will run sweeter and with more power on steam, but you will suddenly discover it has leaks all over the place that never showed with air

Steam is also more fun, especially when hot, oily gunge shoots out of the exhaust all over the workshop and you.

Neil

What I really meant to say (so as not to hijack this thread) was that looks like I now need to look at the timing for the engine if I intend to run on Steam regularly.

I’ve read through all the osts here . Of all the good information I’ve not been able to fit the piece to my situation .

so I’ll give a go here. My little engine is actually two identical engines coupled together . They are double acting piston valve porting . There is the issue. Reading through the post I see note of grub screws. Set screws here in the USA I had a very bad experience in my early engineering career with set screws grub screws . From that point on I really find them disagreeable at best . My little steamer has a number of them and I had a bad experience right atvthe start that resulted in frustration with scared up crankshaft. I had to make a miniature puller to get the flywheel off. What happened was the pistons are attached to the connecting rod by screwing them on then using a hex nut as lock nut. Two cylinders managed to drop the hex nuts then eventually the engine locked up causing everything with grub screws to slip . I had a royal mess. I know many use these without issues but I run my engines a lot. Not fast but often they are shelf modeled. Fortunately the cylinders serviced and I was able to dress off the cylinder heads .

so here is the question the instruction s show adjusting the crankshaft to some position only in one picture. Then to set the piston valve you are supposed to position the eccentric as shown. I can’t post the usual saying. So I started looking for alternat ways to secure the flywheels and eccentrics . I came up with modified shaft collars as well as similar couplers a gentleman did some machine work for me by mailing parts and sketches . Excellent work too. Then I discovered the sample I sent him had 3 mm socket head screws in the cap while the new parts came with 4 mm screws. Now the screw threads interfered as well as the bottom of the counter bore for the screws broke into the relief bore I managed to rework enough screws to clear things but a mess I only have a drill press in my home hobby shop and it’s no a milking machine or lathe I managed to slice sever collars apart ans install heli coils but it’s really make shift at worst. The crank shafts are only 6mm so not real big. The collars take up a lot of shaft length that is un necessary. Anyway I’m just getting things back together and I’m back to the original problem of timing I can find and mark TDC for the piston the steam chest piston port block has an opening in the end so it’s possible to measure the position ofvthe piston valve pretty accurately relative to the power piston I’ll be running on compressed air actually I was only running abou 20 psi when the crash occurred less than 1000 rpm I can get 135 psi if needed but I hope not . Sonibghinknibunder stand how the steam needs to be let in a little early to allow it to expand an do it’s work . Also that steam timing could be radically different than just air timing . My boiler project is on hold for the time being untill I have reliable operation to start with . My plan is some value based on in the instruction picture relative to TDC THEN ADJUSTVTHE ECCENTRIC TONGIVE A LITTLE LEAD TO THE there will be two eccentrics per pair of cylinders pthe ower PISTON. ILL BE ABLE TO MEASUREVTHIS EASILY WITH MY “very near” calipers

the engine crankshafts are made so that once the piston valve is set up the engine will run I have a reverse valve not installed yet but I think this just reversed the intake and exhaust ports according to its instructions . I have air line oiling as well as syringe injection as needed air tool oil works well and 10 W motor oil works to although it’s much stiffer Any way I’d like comments on my timing method . There are sbout 30 YouTube videos but but none address exact measurement like this. I call it “ about measurement “

if I could adjust micro amounts or even greater but measurable it would be fine. I’ll take some pictures of what I have shortly . I’m goingvto assemble the steam chest too there is another issue to look at here too but I’ll get to it later . I hope spell check doesn’t mess this up I just hate it when I come back and have to undo things

byron

Angularity of the eccentric rod means you can't get equal lead and equal port opening. On most set ups the effect is very small but where would we be without a bit of pedantry. 

Edited By duncan webster on 16/07/2022 23:25:40

Why would you think it has been designed with no lead? Just about all the designs for small slide and piston valve engines I have seen have lead often around the 20-30degree mark for steam. Less can be used on air say 10deg

As for the grub screw problem, if the hole is deep enough drop in a slug of brass or soft aluminium and then insert the screw, it will protect the shaft. It is also possible to use the grub screw for initial setting and then when you have the engine running mark the eccentric positions, take apart and file/mill flats for the screw to subsequently bear against which is more secure and no risk of scoring the round surface

Edited By JasonB on 17/07/2022 13:11:22

Thanks forvthe very informative discussion I’ve saved this in three different places so as not to lose it I now have one more question or point I know steam would be the ultimate test but I’m limited to compressed air 130 psi . These engines are pretty small bore and stroke . Both turn over very freely they are linked by a common crankshaft . So far I blocked off air to one steam chest so I realy have only one cylinder operating. I did this as I seemed to be getting alternate pulses as I turned the fly wheel I’m in the middle of measuring the eccentric stroke it’s hard as the piston valve has a threaded hole just large enough that the depth measuring end of my “ very near “ calipers fit into it so I have to hold it at a slight angle . Fortunately it is digital so it’s easy to take full depth then zero it and measure the TDC value directly . Actually easier said than done

so my question is how much air pressure might I have to use? I have a low pressure gage on a short extension . Originally it ran on about 20 psi ive had up to 30 psi now but it still won’t run I’ve been up and down the full stroke of the eccentric but I just can’t get that “ run spot “ or wants to run . I YHINK the piston is only 18 mm with its stroke about 19mm even with pretty leak free connections I just don’t seem to have enough pressure steam would be better for more energy I’m pretty sure . I can hard line all air lines if necessary . I YHINK I’ll do that so I can use more pressure . I’ve had so many interruptions that my time is limited . Live got some brass grub screws coming so I can temporarily plug the piston port end hole. This will give more solid and exact measuring the other half of this engine is just waiting for me to get this half running then I can connect them properly.

byron