Author Topic: Old School Barstock 2 Stroke  (Read 79340 times)

Offline Brian Rupnow

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Old School Barstock 2 Stroke
« on: February 14, 2016, 09:03:28 PM »
In my quest for a simple two stroke engine which I could make from barstock, I looked at many different engines. I didn't want a high rpm screamer with a propellor, nor did I really want to use a design that required me to make rings and figure out how to get them past the ports without breaking them. I also wanted to use spark ignition with Naptha (Coleman fuel) as the fuel, mixed with a bit of 2 stroke oil.--and the potential of maybe experimenting with a glow plug. The 1912 Hubbard Marine engine model seemed to offer up everything I was looking for. It has a 24 mm bore, and a 25 mm stroke, no rings, is water cooled, port induction. and a whopping great compression ratio of 4.45:1. The main body is an aluminum casting with a steel liner. There are videos of this engine running on the internet, and from my research, many have been built and ran successfully. After much messing about, I have come up with a design using barstock which copies all of the Hubbard engines critical dimensions and port dimensions. At first glance, it is uglier than Frankenstein's bulldog, but it does hold a lot of promise.

« Last Edit: February 14, 2016, 09:45:19 PM by Brian Rupnow »

Offline Brian Rupnow

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Re: Old School Barstock 2 Stroke
« Reply #1 on: February 14, 2016, 09:04:31 PM »
I have been able to incorporate adjustable ignition timing, and my old standard Chrysler ignition points. The carb shown is a Traxxas Pro15. The piston and the liner will be machined from cast iron. Almost everything else except the flywheel and crankshaft and crank bearings will be from aluminum. The crankshaft will be "two piece"--that is to say, the main crank, the crank throw, and the rod journal will be 3 parts pressed, pinned, and Loctited together forming one "Piece", which will support the flywheel and be driven by the connecting rod. The other crank throw and shaft which runs out to drive the ignition cam will be pressed, pinned and Loctited together to form the second "piece". This second piece is actually a "follower crankshaft" which is driven by the rod journal fitting with a "slip fit" into the crank throw. This helps greatly with alignment issues between the crankshaft and bearings.



Offline scc

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Re: Old School Barstock 2 Stroke
« Reply #2 on: February 14, 2016, 09:26:51 PM »
Looks beautifully simple Brian, My old Seagull outboard similarly has no oilseals and relies on the oil between the crankshaft and the bushes to maintain crankcase compression. I look forward to following the build.                      Terry

Offline Brian Rupnow

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Re: Old School Barstock 2 Stroke
« Reply #3 on: February 14, 2016, 09:32:45 PM »
This shows the overall dimensions of the engine. I will be posting the detail drawings as I make the individual parts. I will not post them before making the parts, because I have found that quite often the machinist at my house has to go back and remind the engineer at my house that "You can't make it this way!!!---Change the damned drawing please!!!
« Last Edit: February 14, 2016, 09:44:55 PM by Brian Rupnow »

Offline Brian Rupnow

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Re: Old School Barstock 2 Stroke
« Reply #4 on: February 14, 2016, 11:50:46 PM »
Actually, I had another look at the old drawings, and the carburetor has a 1/4" steel ball valve setting in a vertical tube against a seat. The vacuum in the crankcase lifts the ball and draws air/fuel mixture in thru the carburetor. As soon as the vacuum turns to pressure, the ball is dropped back into the seat by a combination of gravity and pressure from the crankcase side.

Offline Brian Rupnow

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Re: Old School Barstock 2 Stroke
« Reply #5 on: February 15, 2016, 02:16:32 AM »
The original plans have an elliptical cam machined on one side of the flywheel, which operates a short stroke piston pump to circulate the water. I don't know right now if I will do the same or not. First thing will be to get the engine to run, with just a plain Jane disc of metal as a flywheel. Then, if I get it to run at all I will worry about refinements like a cam and waterpump. Willy--I'm as confused as you in regards to the glow plug. I have never used a glow plug, but like you I thought they would only work with a "specialty" fuel with a low combustion point. Also, by my understanding, a much higher compression ratio is required to run with a glow plug. The plan set I have says that this engine runs really well with a "glow fuel" and a glow plug, and is very easy to start by hand. It also says that the engine works just fine with a conventional spark ignition system and plain "gasoline" but that it is more difficult to start by hand. I never start my engines by hand anyways. God created variable speed drills to start engines with. As far as a degree plate on my variable timing---No, not likely. I find that the variable ignition timing is wonderful for first start ups. Then, after I find the "sweet spot" where the engine runs best, I lock up the variable timing and probably never use it again. On engines with a wide range of speeds, it is great to have timing that you can advance as you open the throttle. I have seen one of George Britnell's engines that does that, with the ignition advance mechanically linked to the throttle advance.---Sweet!!!. However, this particular engine has a moderate range of throttle induced speed, so I will find the optimum timing setting for a low idle and lock it up there.---Brian

Offline Brian Rupnow

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Re: Old School Barstock 2 Stroke
« Reply #6 on: February 15, 2016, 05:09:37 PM »
This is a totally new one on me!!! I have never seen this type of throttle control and one way valve on a carburetor before. There is a needle valve and metering jet directly below the brown 1/4" ball bearing, which "floats" in the vertical passage. When the piston travels upward, it creates a vacuum in the crankcase, which allows atmospheric pressure to lift the ball of it's "seat" against the tube immediately below it and be sucked into the crankcase, picking up a charge of fuel on it's way past the metering jet immediately below the ball. Once the piston has reached the top of it's movement and starts back down the cylinder, pressure builds in the cranckase, and that pressure, helped by gravity push the ball back onto it's "seat" and prevents backflow of pressure thru the carburetor.----And the really neat thing is that the red screw on top of the carburetor is threaded, and screwing it in or out determines how far the ball can lift off the seat, thus giving throttle control!!! this is very old school, and very clever.---I love it!!! Apparently this system works best with the fuel tank ABOVE the carburetor, depending on a gravity feed to the carburetor, and you must have a fuel shut-off valve on the tank for when you are not running the engine.


Offline cfellows

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Re: Old School Barstock 2 Stroke
« Reply #7 on: February 15, 2016, 05:36:55 PM »
Nice design, Brian.  I tried building a horizontal 2 stroke a couple of years ago.  I, too, didn't want to use piston rings but could never achieve sufficient compression to get it to run reliably.  Hope you have better luck getting a good piston/cylinder fit than I did.

Chuck
So many projects, so little time...

Offline NickG

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Re: Old School Barstock 2 Stroke
« Reply #8 on: February 15, 2016, 05:59:57 PM »
I like the look of this Brian, will read it properly later.

Offline Roger B

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Re: Old School Barstock 2 Stroke
« Reply #9 on: February 15, 2016, 06:06:41 PM »
Looks like you are settling on a design. You will need some sort of valve in the inlet passage if its not controlled by a cylinder port or a rotary valve. Controlling the lift of a ball valve looks to be a good solution.
Do you have a copy of Hiscox's book?

https://ia700508.us.archive.org/2/items/gasgasolineoilen00hisciala/gasgasolineoilen00hisciala.pdf

or on paper

http://www.amazon.com/Gas-Gasoline-And-Oil-Engines/dp/1559182032
Best regards

Roger

Online Jasonb

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Re: Old School Barstock 2 Stroke
« Reply #10 on: February 15, 2016, 06:21:52 PM »
Very similar to a Lunkenheimer carb that has a valve that is lifted by the intake vacuum, closes again and saves the fuel draining back into the tank, found on a large number of hit & miss engines.

I've got to ask why the cooling fins on the head of a water cooled engine?

Offline Brian Rupnow

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Re: Old School Barstock 2 Stroke
« Reply #11 on: February 15, 2016, 07:02:15 PM »
Jason--why did I think you'd be the first person to ask that?--it is basically eye candy. The water cooling is all in the walls of the cylinder, with no cooling at all to the head. Fins are just about the easiest thing to do to a flat plate like the cylinder head. They can't hurt the cooling, and they add a bit of "dress-up" to an otherwise "slab sided" engine. Chuck--I was thinking of you, as I modeled that carburetor, hoping you would see it.--I have not seen a design like that before, and I think it is really neat.--And yes, my primary concern is whether the ringless piston will seal well enough to give the compression required to let the fuel ignite. I did call my local machine shop to ensure that they have a Sunnen hone for back-up just in case I can't achieve the seal I need to.----Brian
« Last Edit: February 15, 2016, 07:07:05 PM by Brian Rupnow »

Offline Brian Rupnow

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Re: Old School Barstock 2 Stroke
« Reply #12 on: February 15, 2016, 07:11:34 PM »
Roger--I am not able to access the link to the "Gas and Oil Engines" pdf. Does the link work for you, or is it perhaps my anti virus keeping me from being able to access it?---brian

Offline Roger B

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Re: Old School Barstock 2 Stroke
« Reply #13 on: February 15, 2016, 07:17:32 PM »
The link doesn't seem to work any more (it was posted by another member in the books/reading section). I do have the pdf, but it's 25MB so I will have to transfer it by Dropbox or similar. I think that I have an email address for you somewhere.
 
Best regards

Roger

Offline Brian Rupnow

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Re: Old School Barstock 2 Stroke
« Reply #14 on: February 15, 2016, 07:24:03 PM »
The link doesn't seem to work any more (it was posted by another member in the books/reading section). I do have the pdf, but it's 25MB so I will have to transfer it by Dropbox or similar. I think that I have an email address for you somewhere.
 

Roger---Thank you

Brian, now that the email address has been read, I deleted it to avoid spammers getting hold of it here in the open forum.

Bill
« Last Edit: February 15, 2016, 11:42:14 PM by b.lindsey »

 

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