My next build--A cross beam vacuum engine

[Brian Rupnow]

The cylinder is made from cast iron.

[Jasonb]

My Cast iron Cylinder flame lickers run OK even the one without cooling fins

[Dave Otto]

My Poppin has a cast iron cylinder, graphite piston and .002" feeler gauge valve and it runs nicely.

Dave

[Brian Rupnow]

Today was a day of rest. No machining, no thinking about machining.--It was great!! This afternoon, I brought my old Poppin engine down to my office to see if it still ran, and where the flame valve was in relationship to the piston position. After  bit of confusion (I couldn't remember which way it was supposed to rotate), away it went, running like a trooper. Now I will try and sort out the timing on my new cross beam engine and see if I can get it to run as well as the Poppin.

[BillTodd]

Looking back at the picture in post # 51, it appears that the cylinder is made from a different metal than the frame.  Is the cylinder made of steel?

If it is, that interjects another thing to consider in your attempt to get it running.  Steel has a lower thermal conductivity than aluminum so it isn't going to "quench" the hot gas as quickly as aluminum would resulting in less vacuum and a weaker power stroke.

It's not really a conductive process Marv. The engine sucks in a flame, which is actually a plasma, it has virtually no thermal mass. The plasma, condenses to a hot gas by losing energy in the form of photons ( the condensation is a rapid phase change like that of steam condensing to water in a Newcomen engine. The collapse of the plasma is very rapid as the energy radiats away, which is how the engines can run as fast as they do.

Ideally, the engine requires the plasma to stay hot enough to fill the cylinder by the time the valve closes (polishing the inside will reduce the photons being absorbed by reflecting them back into the plasma)

I suspect Brian's engine is not filling well , reducing the pressure change, and probably leaking a little too much as well.

[Brian Rupnow]

Okay, it's time to start trouble-shooting. One of the first things I want to look at more closely is the tension spring that keeps the cam follower in contact with the cam. When the engine was brand new and stiffer, I needed this size of spring to ensure that the cam follower stayed in contact with the cam. The engine has loosened up considerably from all of my attempts to start it, and I feel that the spring may now be too strong. When I flip the flywheels by hand, the engine always comes to a stop when that spring is fully extended. Tomorrow I will try successively lighter springs until I find one which still keeps the cam follower in contact with the cam, but is much lighter than the current spring.

[BillTodd]

Brian,

I'm sure your engine will have good compression (you know more about building engines than I ever will)  but , with the slide valve closed does it have a good vacuum seal?   It seems to me the that unless the slide can close over a hole , the atmospheric pressure will force it open.

[Brian Rupnow]

Bill--after reading your original post, I decided that you were right. I had a 1/2" wide brass flap trying to seal a 3/4" cylinder bore. So--I made up a piece of 1/32" wide steel plate with a 3/8" hole in it and bolted it between the end of the cylinder and the flapper plate. Now my 1/2" wide flapper plate seals against a 3/8" diameter hole.

[Brian Rupnow]

I started out this morning to put a lighter spring on the lever which lifts the beam via the cam follower. As I was going thru the motions of doing this, I discovered that one of the joints in my crankshaft had come loose.---PooP!! I had to pull one sideplate off the engine to remove the crankshaft, and decided that I should put a nice radius on the sharp corners of the cam while I had everything pulled apart. Crankshaft was Loctited and set up in my lathe so it would set up "in line" as the loctite dried.---I will pin those joints after the loctite sets up 24 hours. It's noon now, and I'm going to do other things until tomorrow when I will pin the crankshaft and reassemble everything.

[Brian Rupnow]

So, what did I do today? I drilled and pinned the crankshaft--the drills are 0.050" diameter. I drilled the holes .485" deep, then degreased everything with laquer thinners, then rolled the drills in #638 Loctite and inserted the blank end full depth into the drilled holes. I will cut the drills off and sand them smooth tomorrow. I put a 60 degree chamfer on the center hole in the outer cylinder head.--This is what was suggested for the Senft Poppin engine, so I just done the same. It can't hurt and it may help. Then I drilled out my wick-spout on the alcohol tank, to take a larger diameter wick. You can see the small wick size which was previously used and the larger wick which will give me a larger hotter flame. That's all today. Tomorrow I will reassemble everything and hope for better results.

[Brian Rupnow]

No good news so far. I drilled and pinned my crankshaft. I put a chamfer on the small hole in the center of the cylinder head, and I drilled out the alcohol port to take a larger wick. No joy so far.  I may have to put in some new anchor points for the spring that holds the cam follower against the cam. I'm finding it difficult to get a spring strong enough to keep the cam follower in contact with the cam, but weak enough that it doesn't interfere with the free-wheeling motion of the crankshaft (which the cam is attached to).

[crueby]

Hi Brian,  I know you'll get it sorted out.  I don't recall if you have tested the ball-valve you put in on the cylinder, maybe worth trying with that disabled in case that is either leaking or having some other unwanted effect?
Watching along,Chris

[Brian Rupnow]

All I can say about this video is Wow--Wow--Wow!!!

<a href="https://www.youtube.com/watch?v=Kaz6DO86v5I" target="_blank">http://www.youtube.com/watch?v=Kaz6DO86v5I</a>

[gipetto]

>I'm finding it difficult to get a spring strong enough to keep the cam follower in contact with the cam, but weak enough that it doesn't interfere with the free-wheeling motion of the crankshaft (which the cam is attached to).

If there's room you might be able to use a clock spring, the flat type commonly used in pull starters/ seatbelts etc. they have a much longer stretch range than what you're using, and as such don't increase quickly in torque.

[Brian Rupnow]

Gipetto--that's not a bad idea. One thing about having a complete machine shop and spending 58 years as a design engineer--I can make just about anything fit anything else.---Brian