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davidyat

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Finished my current project, Vederstein's Camgine. OK, now what? Well why don't you finish your 1/4 scale Rider Ericsson Hot Air that's been on the shelf for a few years. OK, all buttoned up. The only thing I deviated from was changing the displacer unit from steel to grill brick to make it lighter. Put a flame under it and no go. Yes, the unit is rather tight. So, my question is, how free should the unit be when spinning the flywheel by hand? I still have to free up one connection. When spinning this unit by hand, how many revolutions do you think it should spin before it stops with no heat? Any help would be appreciated.
Grasshopper
 
Hi
During my construction the goal was as close as possible to zero friction / binding. Here was an early stage.



To see all I did to keep it minimal friction go to this build

http://www.modelenginemaker.com/index.php/topic,3441.0.html

As far as how many revolutions, it depends on your compression, the pump seals, etc. Each added part needed to minimally change the above video. As long as it did not just stop dead I was OK. The finished unit runs on about .8 psi gas pressure all day (5hours or so) at shows and you can put your finger on the base next to cylinder and leave it there no burn.

Take the pump off and see if that helps. Are you sure you have no air leaks. I have a valve into the cylinder to demonstrate a closed system , open the valve engine stops dead.

Bob
 
Bob,
Thank you for the reply. At least you've given me a direction to start with. I'm assuming when you are talking about the pump, you're not talking about the water pump? I will disconnect the piston from the cylinder and start there. I will have my set up the same as yours in the video and go from there.
Grasshopper
 
Hi
No I meant disconnect the water pump and see what happens. Try it out again. How big of a burner do you have? Does our hot tube have a copper or stainless bottom, copper is much better as it conducts heat faster. You are looking for any source of bind.

Bob
 
I had the set up like you have in your video. Spins very effortlessly for me. It spins good with the water pump. Then I attached the piston both with and without the piston. Below are 2 videos, one without piston and water pump and one with. I did assemble the heater tube with a stainless steel bottom as per plans. I didn't use a steel heat exchanger inside the heat tube. I read elsewhere on this site, by getting grill brick and turning it down to round that using a rounded grill brick to specs that there would be less mass to move. Just out of curiosity, how much distance should there be between the heat exchanger and the inner wall of the heater tube? So I assembled the engine, put some heat on it, made sure the water pump was pumping water and let it heat up for at least 10 minutes. Not even a fart. Maybe this project will be something to look at on a shelf never to run???



 
In my case the displacer cylinder (heat tube) had an ID of 2". The OD of my displacer piston (heat exchanger) is 1.875. What is just as important is clearance at bottom when the displacer piston is at its lowest. It should be about .031. You want to minimize dead air space when displacer piston is at its lowest. The length of the displacer piston is determined such that you have similar clearance between power piston and displacer piston when power piston is at its lowest point. Did you use high temp black paint on your displacer piston to minimize flaking?

Could you do a video with it all together and just rotate the flywheel slowly by hand so I can see the motion sequence. At least two rotations of the flywheel.

Whose castings are you using?

Bob
 
The castings are from Meyers Engine Works 1/4 scale. I also may have located some problems with my machining. Also you haven't commented on the fact that I'm using grill brick instead of a steel displacer. First off, as I assemble the displacer rod through the Power Piston Center, the displacer piston is NOT centered in the heat exchanger. Next when I looked at the blueprints, I may have NOT looked at the comment, "align the tapped holes for the power piston in the walking beam with the center of the cylinder". Because before just now, I kept thinking, "If those 2 tapped holes were moved a little this way, it would move the displacer more towards the center". Also I can tell there is way more room than 0.0625 inch as you informed me above. (2 inch cylinder, 1.875 inch displacer. Difference of 0.125 divided by 2 leaving 0.0625 clearance all around. I just might make my own heli coil out of aluminum, install in the tapped holes, secure with some Loc Tite (I have some strong stuff) and re-bore and tap new holes to center the displacer better. Then probably make a new displacer to get that 0.0625 clearance all around. Anyway here is the video you requested.
 
I used a grill block also, sort of mentioned it above when asking about paint, see my write up for design. I only used one set of bolts for the power cylinder and displacer cylinder like the original. I could not see any advantage too a bunch of blind tapped holes. Again see my writeup for prints changes.

Bob
 
Bob,
Happy New Year. I've gone through most of your build on PDF. I had originally made the displacer piston per the plans. Then I saw your blog a few years ago and decided to go with grill brick. So I just cut off the bottom portion and left the the small top portion with the set screws. Made a displacer out of the grill block and epoxied it to the round top. What I'll do next is to first make sure the rod moves up and down in the tube centrally. Then, following your PDF, make another grill brick displacer, cut off my original and with the rod and aluminum top installed, turn the unit upside down, re-epoxy the new grill brick and make sure I have equal spacing all around. Or do what you did with the Forstner bit and make another rod, top and piston. When you turn the unit upside down, at least you can look down the tube to make sure everything is centered, put the epoxy on the grill brick, stick it back in and put shims to keep it centered till it cures.
 
My wife is making all our trip reservations this week and NAMES is on it, have not missed one since 1993.

Bob
 
That site does not look real official. Anyway you got it now
 
Bob,
Well, probably in a few days, I'll find out if I have a working engine or a nice paperweight for my desk. I read and re-read your PDF, especially on the displacer piston. I chucked the original grill block and bought and made a new one. As I've said previously, my displacer rod isn't quite centered but does move up and down without hitting the sides. I did get the displacer piston down to 1.880 and the cylinders are at 2.020. I did go and get some irrigation PVC fittings and machined them down to 2.010 OD and 1.885 to use as bushings. Installed the bushings into the cylinder. With the displacer rod and top (the one with the two tapped holes) installed at so called TDC, I put some epoxy on my displacer piston (grill block) and pushed it through my bushings to meet the top. Hopefully the bushings will keep the piston centered as it rides up and down with 0.0625 space around the piston and cylinder. I did it this way as I'm trying to use what I've machined and make it smooth and hopefully easy moving. I see what you mean about painting the grill block. When I tried to see if it would work with the old grill block without paint, not only did it flake, but chunks at the bottom popped off. I hope to see you at NAMES this year with a working engine instead of a paperweight?
Grasshopper
 
I am a bit concerned about the PVC bushings. It gets real hot in that cylinder, you need to make sure they will not melt. Not sure what the bushings are for, where do they go?

Bob
 

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