My next build--A cross beam vacuum engine

[Jasonb]

Don't make it a thick chunky thing, get the piston as light as possible say 1/16" wall thickness max and also the crown as thin as possible.

These were my comment son HMEM about piston's to Brian for those following here

As I posted earlier in the thread a Utility knife blade is quiet common and what I use on teh CHUKY. The Grey Nattie that I showed has a shutter cut from 1/2 x 1/16 flat steel strip.

Nattie shutter, slot is no more than half a thou deeper than the shutters thickness

The CHUKY is running a piston turned from Cast Iron bar lapped into a CI bar cylinder. The Nattie uses a spun brass piston that wa sfinish turned and then lapped into the cylinder which is an iron casting.

CHUKY has a very different cam profile to yours, closed for longer than it is open

[Brian Rupnow]

For those of you who are following---Today I made a new cast iron piston, left it about .001" to .002" oversize and lapped it into the cylinder with 600 grit lapping paste. The bore of the cylinder measures exactly 0.75" diameter. It was reamed to size with a 0.75" reamer when first made, then honed with a 3 stone brake cylinder hone. The brake cylinder hone probably opened it up .0001 to .0002", but my measuring equipment won't measure that anyways. The graphite piston was turned to an exact 0.75" and was a snug fit into the cylinder when first made.  This morning when I removed the graphite piston, it measured 0.745" in one plane and 0.747" in the other. It was a sloppy fit into the cylinder, and if I tried to spin the flywheels with my thumb held over the end of the cylinder, it had no "bounce back" at all. I really don't trust graphite for a wear item like a piston, and probably won't use it again.  The slot I milled in my cylinder head was milled 0.030" deep, and I used a 0.020" feeler gauge for the flap valve. I have since spoken to Jason from the U.K. and he tells me to use a flap valve about 0.001" to 0.002" less than the depth of the machined groove. Since I have already used  a feeler gauge to make the first flap valve, I don't feel so bad about cutting off a 0.028" blade to make another flap valve.

[Brian Rupnow]

Well boys---I think I'm whipped!!! My new cast iron piston and thicker flap valve hasn't made the magic difference. I've tried pre-heating the cylinder. I've tried it with only one flywheel. I've played with the timing. I've tried it with the "smoke-stack" taped shut. I've tried it with the propane torch blowing directly on the flame hole in the cylinder head. I've tried every trick in my arsenal, and it's not happening. This is a big disappointment to me, as I truly believed I would have a runner. I have no tricks left to play, and now I have to think about what to do next. I may reconfigure all of my parts to make a different style of flame licker. I may take up tap dancing instead of machining as a hobby.

[Brian Rupnow]

The profile of the cam is the only part of this engine which I am not sure about. I am using the same cam profile as my "Poppin" engine which I built and ran successfully about 5 years ago. The profile needs to be such that the valve flap is open when the piston goes from tdc to bdc to suck in the flame. The valve must close very quickly at the end of this stroke, so that the flame sucked into the cylinder goes out and creates a vacuum. The vacuum sucks the piston back to tdc, the valve opens, and everything repeats.

[gipetto]

It's most likely the cam then. Your situation reminds me of my father who had a tractor engine that boiled, he replaced everything, radiator, water pump, etc on the advice of a shopkeeper but couldn't find the issue, it broke his heart. he sold it to a mechanic who line bored the crankshaft and resold it to a man who owned a sawbench. some years later, he bought some wood from the sawbench and enquired about how the tractor was running, owner said it was the best machine to come into the place. (it had to be because every part was new on it)
anyway i think that when you do get it running it will run like a dream, because you have eliminated ever minor issue first.

[Jasonb]

The popping engines shutter moves away from the port rather than slides across it as you have on the beam engine so is unlikely to be giving you the correct timing.

What timing do you have at the moment - starts to open, fully open, starts to close and fully closed ?

[Brian Rupnow]

I spent some time this morning laying out a device to keep pressure on the flap valve so it would seal tightly against the end of the cylinder.  Decided that yes, I could do it, but it sets directly above the hole in the cylinder head and would die a pretty quick death from the alcohol flame.--There is a compression spring in that assembly that I didn't show.

[Brian Rupnow]

Jason-- flap fully opens about 15 degrees before top dead center, stays open during intake stroke, closes very rapidly as piston approaches bottom dead center, stays closed until 15 degrees before top dead center, then cycle repeats.

[Jasonb]

Sounds like you have the shutter open a bit too long, try to have it open the flame port about 5deg before TDC and close about 25deg before BDC

[Brian Rupnow]

The might Casey has struck out----I tried out a different cam shape and the new cam didn't make any difference to the way the engine ran---should I say didn't run. I've used up all of August and 12 days out of September on this engine, but it's a no go. It's not a total loss--I can re-use the alcohol tank, the crankshaft, con rod and piston, and the cylinder, maybe even the base. Not sure at this moment what type of engine I will use them on, but they will get used. Time for me to give machining a break for a while. I really expected to have a runner here, but it's not going to happen. I'll be back when I have decided what I'm going to do.---Brian

[Brian Rupnow]

I went to bed last night thinking of how I can re-use most of the parts I have made on a four cycle petrol fueled engine. This morning I came downstairs to my office and designed what you see here. Everything is re-used except for the cylinder head and the funky side plates and the cross beam. A new cylinder head and conventional valves and valve guides can be made to work.  Working with this software is just like a drug---I can get lost in it for hours. I will probably finish this new engine design and then start a new thread about it's development.---Brian