Horizontal Air Cooled Engine

[brian Rupnow]

Yesterday I finished designing a welding fixture for one of my old customers. Earlier this week I redesigned one of the cylinder heads for my opposed twin engine, seeing how I could relocate the sparkplug up near the top of the cylinder head. I don't really want to mess with a finished engine, so I decided to design a new engine to go with my redesigned cylinder head today. Of course this leads me right down the garden path, and seven or eight hours after I think of it, I've designed it. This engine will be air cooled, and will have two valves and a throttled carburetor. I've put a 2" diameter fan on it, and even designed a fancy fan shroud to support and guard the fan blades. I'm not sure when I will get around to building this one, but winters coming and I will need something to do----

[brian Rupnow]

And a couple more views so you can see where this one is going---

[brian Rupnow]

Today I made the first part for this engine, the cylinder mounting plate. I used my new bandsaw, and what a wonderful bandsaw it is. It zipped thru the aluminum as if it was butter. This is the first part I have made using the new bandsaw, and all I can say is, I wish I'd bought it ten years ago!!!

[brian Rupnow]

People on another forum commented on how ugly that carb arrangement was. The more I looked at it the uglier it looked. I haven't built anything on the head yet, so I was able to go in and change it---carb comes straight out the side now. I left that big air horn that was on the front of the carburetor off too.

[Cuttings]

Good morning Brian. Looking pretty good so far. I noticed one thing. How are you going to get the belt on the fan pulley ? Maybe the fan guard bolts together.

[Lew Hartswick]

The gear ratio "LOOKS" more than 2:1 . May just be my eyes. :-)
...lew...

[brian Rupnow]

The gears have 20 and 40 teeth. Getting the belt on will be a trick.--That fan design is just a quicky, it will have a bolt on fan support strap when I get to it.---Brian

[brian Rupnow]

Today was spent making sideplates. They are finished except for tapping a bunch of holes. I have used up my entire day machining these parts, and will do the tapping tomorrow.

[brian Rupnow]

I had a stroke of good luck this morning. After tapping something like 20 holes, and assembling things, I discovered a length of 01 steel with two cams cut on it. The last time I set up to cut cams I decided to cut over-length while I was in the set-up for use on a potential future engine. The future has arrived!!!

[brian Rupnow]

--I picked up my cast iron today to make the cylinder. The only material that my supplier had in stock was 2.1" diameter ($25 for 4"). I haven't made the cylinder yet, but this gave me an idea. Without changing anything, I can make it look like this if I want to. This shape harkens back to some of the early model two cycle airplane engines that were made in the 1930's to 1950's. I kind of like it.

[aostling]

You ordered the book "Model petrol engines: their design, construction and use" from Amazon. Westbury advises (on p.168) fins on the cylinder head, which is prone to overheating. Fins on the cylinder are not so important on a small engine.

[darryl]

Thanks for the smile Brian. I know you said you'd need something for a winter project, and now you're already building it. You are the model engine man. So- what are you going to do for a winter project?

[Dan Dubeau]

You ordered the book "Model petrol engines: their design, construction and use" from Amazon. Westbury advises (on p.168) fins on the cylinder head, which is prone to overheating. Fins on the cylinder are not so important on a small engine.

One would think it depends a lot on the orientation of the cylinder no? Yeah a lot of heat would propagate through the head, but less so in a horizontal than a vertical? I wonder how much of an effect that would have.

And I agree with Darryl. This isn't a "winter project" You'll have this done and running before the now flies .

[J Tiers]

One would think it depends a lot on the orientation of the cylinder no? Yeah a lot of heat would propagate through the head, but less so in a horizontal than a vertical? I wonder how much of an effect that would have.
...............

Much of the heat is from the exhaust which flows through the head, plus much of the cylinder has hot gas in it for only a very short time. The head sees it all the time it exists. (for 4 cycle engines, 2 stroke may exhaust out the cylinder wall).

Temperature of the head is not much affected by position, unless that affects cooling..

[brian Rupnow]

This morning I made up the main baseplate. This plate has an interesting feature in it. In order to keep everything small, a scallop was cut from the baseplate to clear the 40 tooth cam gear.