Oscillating I.C. Engine

[Brian Rupnow]

Allen---I can tell you have been married for a while, like myself. As far as any kind of ducting is concerned--I find it extremely difficult to make up any kind of ducting that doesn't come out looking rather "crude" on these small engines. ---Brian

[Allen Smithee]

A bit of thin sheet brass with a plethora of rivvets and the odd bit of chasing or planishing can give an engine a pleasing "steam-punk" character...

PDR

[Brian Rupnow]

Something unusual here---In his book 'The Shop wisdom of Philip Duclos' where these plans originated, Philip specifies the use of "Hot rolled or cold rolled steel" for the cylinder. He specifies cast iron for the rings. Okay--I can see the need for the strength of steel as opposed to cast iron because of the two pivot bosses on the outer walls of the cylinder, but I have never seen steel specified for a cylinder before.  I don't think that it is a mistake. I'm just very curious as to whether steel will work satisfactorily for the application.--Any opinions??----Brian

[Brian Rupnow]

I really wish I could make the cylinder from aluminum, it would be so much easier to machine.  Almost every plan I have ever seen calls for the cylinder to be cast iron, and any that have an aluminum cylinder always call for a cast iron liner. I know, my weedeater, chainsaw and lawn mower all have gas engines with aluminum cylinders, and they seem to get away with it just fine. The aluminum I use is just common bar stock purchased from my local metal supplier, and I have never asked what grade it is. Probably 6061, but I'm not sure.  I don't know if all the other hundred million small engines with aluminum cylinders are running some special aluminum material that I don't have access to. I hope I get some more insight into this before I actually begin the build process.---Brian

[gbritnell]

Hi Brian,
You're correct that a great many small engines have aluminum cylinders the only difference is that the aluminum that's used has a very high silicon content. Out of the readily available aluminum grades being sold I don't know which one I would recommend to use. If you've ever bored a nice smooth hole in aluminum then tried to slide a close fitting shaft into it the first thing that generally happens is it will gall and freeze up. Naturally with an engine you're going to have some lubrication but I still would be skeptical. By the way, how are you going to lubricate your piston, with oil in the fuel?
gbritnell

[Jasonb]

If you are basically using the Duclos sizes then you should still have room to put in a steel or iron liner, would not go much over a 0.050" wall thickness to save weakening the cylinder, small lip at the top so it is held in position by the head.

You will also need to take a look at the pivots if those supports are also from aluminium, as you don't want ali running in ali, probably have to press a thin bronze sleeve onto the pivots, a matching one in teh support would also be nice to have as well.

[Allen Smithee]

The engines with aluminium cylinders generally have plated bores to avoid wear and galling. I haven't actually tried it, but I'm fairly sure that it's not possible to lap an unplated aluminium part (cylinder or piston) because I'd expect the lapping compount to irretrievably embed itself int the surface of the aluminium. So that means you're stuck with sizes and finishes that you can machine directly. Now while I appreciate Jo will soon be able to shave the sides off neutrons with her Hardinge, many of us would struggle to get a good-enough piston/bore fit & finish without lapping.

PDR

[Ian S C]

A cast iron piston/ piston ring will run in a steel cylinder with very little difference in friction or wear than a cast iron cylinder.
This is the steel cylinder, and cast iron (window weight iron) for a Stirling Engine stove top fan.
Ian S C

[Brian Rupnow]

George--I haven't got that far yet. If I run Viton o-rings as piston rings, then I have to use a bit of oil mixed with the fuel. If I take another shot at making cast iron piston rings, then I will probably add an oil cup to the cylinder.---Brian

[cfellows]

Brian, have you thought of making the cylinder from aluminum then pressing in or loctiting in a piece of thin wall brass tubing for the liner?  I've never tried it but it it seems like it would work OK.  By the way, I've used 12L14 leaded steel for cylinders and it works fine.  It also machines darn near as easily as brass.  I know that Terry Mayhugh, my friend here in Texas also used 12L14 steel for the cylinders on his 18 cylinder Radial engine.

Chuck

[Jasonb]

Yep just done a steel cylinder myself with plenty of fins and found it very nice to machine. Seems to me the slight ease of changing from the Duclos steel design to Aluminium will create more problems that will need as much if not more work to overcome. A liner still won't address the problem of ali pivots in the ali supports.

J

[Brian Rupnow]

If I make the cylinder from cast iron, it will be fairly easy stuff to work with. The only issue I see with cast iron is that the bosses on the sides will be fairly delicate---will need to use a very sharp tool when machining them or they will pop right off of the main cylinder block.--(Don't ask me how I know this!!) However, the bore and fins are pretty easy to machine in cast iron. If I make the cylinder from aluminum it will be super easy to machine, and will be very "flashy", but I don't think the pivot bosses would last very long, and I don't know how the bore would stand up to interaction with a sharp edged cast iron ring on the piston.--Would probably be okay with a Viton ring and a bit of oil mixed with the fuel for lubrication. --Could possibly press fit a thin bronze bushing over the cylinder bosses to take the "wear factor" from oscillating. Steel would definitely be the material of choice in regards to strength and wear factor of the pivot bosses, and it wouldn't be too bad to machine the bore and the outer shape and the bosses.--Could however, be a real "bear" to machine the fins into. I plan on using an HSS slitting saw to cut the fins.--Decisions, decisions--

[Brian Rupnow]

The cylinder is pretty simple. The slots which create the fins are the scary part. I know my small mill does a great job cutting .094" wide x 3/8" deep in aluminum. Probably it wouldn't grunt at cast iron. Steel though---Ah, Jeez, I'm not sure about that.

[spuddevans]

Following along quietly here Brian (until now) Nice design.

The cylinder is pretty simple. The slots which create the fins are the scary part. I know my small mill does a great job cutting .094" wide x 3/8" deep in aluminum. Probably it wouldn't grunt at cast iron. Steel though---Ah, Jeez, I'm not sure about that.

A slitting saw would work easily in cast iron, just take it easy on the feed.


Tim

[Brian Rupnow]

Or---How about an alternate design--aluminum cylinder with radial grooves (easier to make on a lathe), thicker cylinder wall, and hard press fitted steel pivots?