Manson Hot Air Engine Build

Topics include, Machine Tools & Tooling, Precision Measuring, Materials and their Properties, Electrical discussions related to machine tools, setups, fixtures and jigs and other general discussion related to amateur machining.

Moderators: GlennW, Harold_V

User avatar
rmac
Posts: 786
Joined: Tue Jun 26, 2012 12:48 am
Location: Phoenix, Arizona

Re: Manson Hot Air Engine Build

Post by rmac »

Thanks for the offer, Harold! I've sent you a PM.

-- Russell Mac
pete
Posts: 2518
Joined: Tue Feb 10, 2009 6:04 am

Re: Manson Hot Air Engine Build

Post by pete »

Fwiw maybe a few more thoughts Russel. Simple drilled holes may not be all that straight, to size, most certainly not round or have a great surface finish. All that contributes to possible binding and more friction. George Thomas made a point in one of his books that when using fractional sized reamers they almost always cut a few 10ths or more over there listed dimension. So he'd make and polish the pins to that miked nominal size and have right around the correct clearance fit in fractional sized reamed holes. The same idea would work with letter, number size or decimal reamers also. As he said it saved a lot of time turning and trial fitting the parts in small assembly's for the correct close but slip fit. I think you'd find a few reamers in the sizes your needing isn't all that expensive and create a lot less friction. Looking at your last picture shows it's a horizontally arranged engine. Gravity is also very much working against you for creating more friction on both those pivot points simply because the larger surface area moving parts are resting against the fixed non rotating parts. Cutting enough extra clearance to allow the use of small thin plastic washers between those parts might help a lot. Starrett makes a non drying proper instrument oil that might be very helpful for any non heated areas. Graphite should work well for a dry lube where the parts become hot. You wouldn't need much and crushing up a few pencil lead refills used in mechanical pencils to a fine powder is easy to find and dirt cheap. I've no idea of cost, but I've seen it mentioned more than a few times for hot air engine building that many use what's called machinable graphite to build there complete pistons to get ultra low frictional drag. Very messy to machine obviously, so if you ever try that I'd cover your lathe as much as possible and use a shop vac to collect the dust as it's being created.
User avatar
rmac
Posts: 786
Joined: Tue Jun 26, 2012 12:48 am
Location: Phoenix, Arizona

Re: Manson Hot Air Engine Build

Post by rmac »

Thanks, pete, for even more great hints, especially about the reamers and pins.

Lots of the folklore surrounding these little hot air engines suggests that they run best without any lubrication at all. Folks even go so far as to flush out the oil from brand new bearings. Apparently the drag induced by the viscosity of even the lightest oil can be greater than the friction it's supposed to reduce. And in fact I've seen that to be true with both my Stirling engines and this new one. They all run better dry. The Manson engine is now behaving more or less perfectly since I cleaned off all the oil and it's had a chance to "run in" a little bit.

And guess what ... you're right about the horizontal orientation of the flywheel. I flipped the whole engine 90 degrees and it runs way faster with the flywheel in a vertical plane. Gonna have to start worrying about that 10K RPM redline. :D

As I mentioned earlier, I'm still thinking about making a second, improved copy of the Manson engine. A really simple connecting rod would be just a short length of rod with a ball bearing stuck on each end. I wonder if a guy could silver solder the rod to the bearings without destroying the bearings. My gut says no, but it might be worth a try.

connecting_rod.png

-- Russell Mac
pete
Posts: 2518
Joined: Tue Feb 10, 2009 6:04 am

Re: Manson Hot Air Engine Build

Post by pete »

Yeah I can see where oil or even the parasitic drag between the parts oil causes might be a problem. But that graphite in small amounts also might reduce the friction by quite a bit. More money but some ceramic bearings with zero lube might be even better. This would be the place for them or about any other small bearing. https://www.bocabearings.com/ Those ceramic bearings are used by the home builders of R/C jet turbines because of the 120k-200k rpms. In those they have a pumped oil mist supply that's a total loss system through the bearings. I'm pretty sure the lube also helps keep the bearing temperatures down at those speeds. Even with all that there bearing life is pretty short. At your rpms and no oil it wouldn't be a problem. I've never tried soldering directly to the outside of a bearing race so can't help there. I'm not sure that hard soldering temperatures might not upset the heat treatment in the balls and races or possibly warp the outside race enough to matter.

Almost anything will run at high rpms, just how slow you can go measures how well the whole engine alignment is and all the friction reducers you can think up. Removing weight by cutting into both sides of your flywheel leaving maybe .125" in thickness and pressing a steel rim onto the outside rim you already have will greatly increase that flywheel effect for a lot slower running. But physics can't be scaled down. The larger the flywheel diameter is the more you'd see a difference when adding a heavy steel rim.
User avatar
Harold_V
Posts: 20231
Joined: Fri Dec 20, 2002 11:02 pm
Location: Onalaska, WA USA

Re: Manson Hot Air Engine Build

Post by Harold_V »

rmac wrote: Mon Nov 01, 2021 11:59 pm I wonder if a guy could silver solder the rod to the bearings without destroying the bearings. My gut says no, but it might be worth a try.
Not with silver solder. Silver bearing solder, maybe, assuming you could do the soldering without contaminating the balls/races. I suspect that even that would be a poor idea, though.

Silver soldering would exceed, by far, the annealing temperature for the bearings, to say nothing of the damage done by oxidation and distortion.

H
Wise people talk because they have something to say. Fools talk because they have to say something.
tscoupland
Posts: 2
Joined: Sat Sep 04, 2021 10:08 am

Re: Manson Hot Air Engine Build

Post by tscoupland »

rmac wrote: Mon Nov 01, 2021 11:59 pm
As I mentioned earlier, I'm still thinking about making a second, improved copy of the Manson engine. A really simple connecting rod would be just a short length of rod with a ball bearing stuck on each end. I wonder if a guy could silver solder the rod to the bearings without destroying the bearings. My gut says no, but it might be worth a try.

-- Russell Mac
Hi Russ
As you know I have been a bit busy of late, so no time to log in to see what you are up to.
Glad all of my offline help got you going in the end.
Well done for building a working version.
Much better machining than the prototype I built to prove the design https://www.youtube.com/watch?v=eBqhPVnxTKY


Con-Rod
I still think a simple flat aluminium con-rod with the bearings pushed in place would work ok, like in the Fusion design I sent you some weeks ago.

Tim
User avatar
rmac
Posts: 786
Joined: Tue Jun 26, 2012 12:48 am
Location: Phoenix, Arizona

Re: Manson Hot Air Engine Build

Post by rmac »

Harold_V wrote: Not with silver solder.
pete wrote: I'm not sure that hard soldering temperatures might not upset the heat treatment in the balls and races or possibly warp the outside race enough to matter.
Tim wrote: I still think a simple flat aluminium con-rod with the bearings pushed in place would work ok,
Okay, no bearings will be sacrificed!

I saw this engine for the first time just now on YouTube. Note the interesting yoke mechanism instead of a connecting rod, and the really nifty flywheel with a clear plastic web.

yokie.png

-- Russell Mac
User avatar
rmac
Posts: 786
Joined: Tue Jun 26, 2012 12:48 am
Location: Phoenix, Arizona

Re: Manson Hot Air Engine Build

Post by rmac »

Time for an update. As advertised, I wound up starting over on a second, hopefully improved version of the Manson engine. In Fusion 360, it looks like this:

manson_iii.png

I'll probably do something fancier with the flywheel than the drawing shows. The displacer, the piston, and their respective cylinders are all the same as before except I think I got a little bit better piston-to-cylinder fit this time. As pete suggested, I've tried to reduce friction in the rest of the engine by changing the flywheel orientation and by putting ball bearings at each end of the connecting rod. The new connecting rod also weighs a lot less (1.3 vs 8.6 grams) than the previous one.

Here's the new connecting rod with its connection to the piston. Both ends of the connecting rod are the same. There's a little 1/8 x 1/4 x 3/32 ball bearing hiding in that clevis somewhere.

new_connecting_rod.jpg

On the connecting rod, I wound up using the scribe-and-grind-to-the-line method to cut the outer profile. However none of the tricks we discussed in the other thread really worked for the round clevis on the end of the piston. So I wound up setting up the rotary table after all to round over its end. Good thing I don't have to make a living at this.

-- Russell Mac
User avatar
rmac
Posts: 786
Joined: Tue Jun 26, 2012 12:48 am
Location: Phoenix, Arizona

Re: Manson Hot Air Engine Build

Post by rmac »

rmac wrote: I'll probably do something fancier with the flywheel than the drawing shows.
Like this:

flywheel.jpg

All that fooling around with trepanning last summer finally paid off.

-- Russell Mac
User avatar
rmac
Posts: 786
Joined: Tue Jun 26, 2012 12:48 am
Location: Phoenix, Arizona

Re: Manson Hot Air Engine Build

Post by rmac »

All done at last. I'll try to post a video of it running if I can figure how to do that.

Right now I'm using some 1/4" nylon rope for the wick in the little alcohol burner. It works okay most of the time, but sometimes the end melts and burns and leaves a gooey black blob that I have to cut off. I suppose something like that would happen with any material, but I wonder what a "proper" wick would be made of. Anybody know offhand?

-- Russell Mac

manson1.jpg
manson2.jpg
pete
Posts: 2518
Joined: Tue Feb 10, 2009 6:04 am

Re: Manson Hot Air Engine Build

Post by pete »

Looks great Russell. Afaik wicks are made of cotton.
User avatar
rmac
Posts: 786
Joined: Tue Jun 26, 2012 12:48 am
Location: Phoenix, Arizona

Re: Manson Hot Air Engine Build

Post by rmac »

Thanks, pete. I tried some cotton rope also and it slowly gets charred and shorter about like the nylon stuff.

Tim Coupland suggested trying the stainless steel wicks sold by Kontax Sterling Engines in the UK. I've ordered one to try, but it hasn't arrived yet and it's not clear how big it is. If it works, at worst I'll have to remake the spout on the little alcohol burner. Might be worth experimenting by just twisting together a bunch of wire to approximate the Kontax wick. I think I'll go do that right now.

-- Russell Mac
Post Reply