Simple Valveless Engine

[PaulR]

Fixed the bearing standard in place, finished the crank disc and pin. The disc could be made a lot smaller as this size was to accommodate the original plan with longer stroke but the extra bit of momentum might help 'get it over the hump'.

Removed the temporary screws underneath and countersunk the holes for the only screws I've got left - had to go a bit deeper as they're not very long. I didn't realize the countersink was going to be quite so close to the edge before I started - phew!

[PaulR]

It was time for the fiddly bit... the holy piston. Decided to make it from square bar to make drilling the various holes easier. First off the long exhaust and shorter intake holes.

Mistake #1 After marking and centre punching the end I set it up in the 4-jaw with a floating centre but no matter what I did I couldn't get the thing centred. It was driving me nuts! I took it out of the chuck, took away the DTI, cleaned everything, checked nothing was loose or out of kilter then put it all back. Same problem  I'd spent almost half an hour on this when I realised what I was doing - setting the plunger on the bar instead of the centre  I think it was because I'd centred the bar on the previous operation to mark the hole positions etc. Oh how I laughed. Not.

After drilling the longitudinal holes:



Drilled the inlet hole:



And the exhaust:



Must get that drill sharpened, it's creating a crater rim of a burr! Put the back in the lathe, centre it up and started turning to diameter.

Mistake #2 Realised I'd forgotten to drill the cross hole for the clevis at the end of the piston      Fortunately I hadn't got far so there was plenty of flat surface to hold in the vice to get the drilling done:



Back in the lathe, re-centred then turned down to diameter:



It's possibly a fraction loose except at the far end where the bore will need a little attention Despite regrinding the tool three times during turning I couldn't get the finish I was hoping for but hopefully it'll be good enough.

There we have it, warts and all! A less than optimal session, hopefully the next one will be smoother. I just need to remove that stub and cut a slot for the connecting rod - might leave that until later in the week when I hope to get something to make holding work in the vertical slide more reliable from the ME show (a vice, some parallels and some aluminium packing).

[PaulR]

Very brief morning session, did a bit of cajoling to get the piston fitting nicely and threaded the cross hole at the other end.

[PaulR]

Chopped off the square nubbin and faced the end of the piston, made the con rod and the flywheel apart from the securing grubscrew. Just need to cut the slot for the con rod and it'll ready to try.

[PaulR]

Another short session: turned down the end of the piston (was going to leave it same dia as piston but what the hey), tapped for the flywheel grubscrew and used emery cloth to reduce the conrod from 1/8" to 3mm thickness. Just the slot and the screw for the piston end of the rod and it's done.

[PaulR]

Finally found time to finish this (with the exception of one screw - no prizes for spotting it  ) and gave it a try on air.

It was close to going when the pressure was very low (a few psj) but not a chance when the pressure was increased. I made a larger flywheel to see if that would help but the difference was marginal if any. The next thing to try was opening up the inlet port on the piston so I increased the hole from 3mm to a countersunk 4mm which would get the air in sooner but on the downside also create more air to be compressed. It seemed to make a small improvement but it still wouldn't quite go so I increased it another 0.5mm but that seemed to make no difference. There might be room to increase the size of the exhaust port a tiny bit so it opens earlier, beyond that I can't see what else could be altered except for making the entire exhaust hole bigger.

[Charles Lamont]

It might need more than a flip of the flywheel to start it. Have you tried a starting it with a string wrapped a few turns round the flywheel?

[PaulR]

It might need more than a flip of the flywheel to start it. Have you tried a starting it with a string wrapped a few turns round the flywheel?

No, but the engine is very free running and will do quite a few rotations when not hooked up to air.

[PaulR]

It might need more than a flip of the flywheel to start it. Have you tried a starting it with a string wrapped a few turns round the flywheel?

No, but the engine is very free running and will do quite a few rotations when not hooked up to air.

Gave it a go but it didn't work although it makes a nice sound for the brief time the engine is running! Seems like there's insufficient energy in the flywheel to compress the remaining air...

[PaulR]

After more tweaking I still can't get this to run so I'm putting it down to experience. At least I've pleased the half of forum members who said it wouldn't work 

[vtsteam]

Maybe some day you will revisit this, Paul. Why not? The concept is (to me) sound. Just the details, maybe. I think your piston is too heavy. Make a new one? Make it shorter, and aluminum. Get rid of the ported exhaust and simpler, just uniflow it.

Here's a very crude pic, where I mangled yours -- just a schematic, not to scale (especially the gross unflow port(s) I hamfisted in here, or working chamber volume and timing. The devil is always in the details, but stick with it and you will make it work -- er that's my belief anyway!

(btw.....ya kin always plug holeses, ya know...)

[PaulR]

Maybe some day you will revisit this, Paul. Why not? The concept is (to me) sound. Just the details, maybe. I think your piston is too heavy. Make a new one? Make it shorter, and aluminum. Get rid of the ported exhaust and simpler, just uniflow it.

Here's a very crude pic, where I mangled yours -- just a schematic, not to scale (especially the gross unflow port(s) I hamfisted in here, or working chamber volume and timing. The devil is always in the details, but stick with it and you will make it work -- er that's my belief anyway!

(btw.....ya kin always plug holeses, ya know...)

That's a good idea, I'll have a think and redraw the relevant bits once the current project is done.