Monday, September 8, 2008

Adding push rod guides, need to replace 1 case piece

I could see from the push rods bending when I turn the engine over, that there was a lot of lateral force from the curved edge of cam. I believe this was causing the pistons to rub too hard against the sealing bags. After cutting the guides to center of where the rods travel, I discover that one of the case pieces has its push rod shaft slight off center. So now I have to make a new one. I may just drill the guide pin hole in push rod to compensate instead.

I also realize now that the the direction of wrist pin should be parallel to the shaft rather then perpendicular like it is in a crank based engine. With the cam driving the piston, the lateral forces from the curve of the cam will translate to pressure against the wall of cylinder. The push rod of this design can slide along the wrist pins, if the pistons are rotated 90 degrees. This along with the guides should reduce wear of the piston seals.

I just got found another older digital camera, so I can keep it handy and try to take more pictures. I apologize that I haven't taken too many.


Gustav Johansson said...

This is so cool. I'm a Swedish student doing the exact same thing as you do, making a free version of the Stirling engine. Even more strangely, I have the exact same name of the project and we started at the same time, in the begining of July. You can see for yourself at, but everything is in swedish so you probably wont understand anything (well in the begining, my project was called "stirlinginafrica" but I have changed)

It would be awesome if we could contact each other by mail, please!!! do so my mail is

Sorry for my sometimes bad English, but I hope you can understand.

//Gustav Johansson

Tom said...

Hi Gustav,

Thank you so much for your comments. I hope some of the lessons from my project will help you with yours.

I used Google to access your site and have translate it to english, so I could read it. Looks like an interesting project. Please keep us up to date with your progress. I also have a Google website for my project and will add a link to your site from there too. That will be where the official documents will be posted to.

I also have some Google documents, which I haven't published yet, but am willing to give you access to. They are very rough and need much work before I would publish them.

These documents include:
Spreadsheet with a partial parts list with dimensions, thermodynamic calculations for volume ratio, temperature difference and cam size.
Some dimensions from other diagrams if found on the web, where I scaled the pixels so the cylinder diameter is 2". There were 2 diagrams and I kind of averaged, the sizes.

Very old presentation, that includes the images I used for the spreadsheet. Tell me if you want to view them and I will add you as collaborator.

Good luck,

- Tom Belpasso

I assume my response will be mailed to you.

Gustav Johansson said...

Yes I would very much like to see your documents. Interesting that you have made thermodynamic calculations on each pieces.

It seems like we are doing to different kinds of Stirlingengines, although I havn't started yet. It will be exiting to see which is more effective. I will begin my construction of an not free engine next week, found a blueprint on the Internet

Are you doing this as a
school project or just for fun?

Tom Belpasso said...

Hi Gustav,

In order for me to share my Google documents with you, I need your e-mail address. It seems Google is protecting us.

As far as my motivation, just trying to save the world.

Soon I will explain all the engineering trade off and rational for the current design.

Please send me your e-mail address, preferably a Google account and will give you access to some of my documents.


- Tom Belpasso

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