Stirlingengineforum.com

Hello. I am a newbie to Stirling Engines. Thank you for a wonderful site.

Recently, my daughter and I began work on the Dr. Senft LTD Stirling Engine that he details in his amazing book. We’ve made the parts, got to the testing phase and hit a snag. I’d like to run down our thinking so far and ask for feedback or direction.

It seems that no matter how we angle the displacer link, we either hit the top or the bottom plate. We’re using an Airpot cylinder and that seems to be perfectly fine.

We think this means that either the displacer chamber is too short or the distance between the axle center and the displacer bearing is too large. As far as we can tell, both are within tolerances, so we’re scratching our heads here. We could remake either. However, it seems that we should remake the axle assembly to be a shorter distance since he was very specific about the size of the displacer chamber.

Secondly, o-rings. We didn’t (but should have) counterbored the displacer gland and the base block for o-rings. We were a bit shaky on our lathe skills. Now that we’ve made every piece, we are confident enough to counterbore should the need arise. Also, the plans call for a groove to be cut on both ends of the displacer chamber ring for a large o-ring. Any reason a think piece of cork wouldn’t work instead?

We have a few other things to tweak, but I believe these are the major issues. I hope my descriptions are clear.

Thank you all for any advice.
Mosa

Mosa, I'll try and help, I design and build my own motors. I'm not familiar with your motor, determine which end of the displacer is hitting the end, and either shorten, or lengthen the con rod, there should be an equal gap at each end. The displacer leads the power piston by 90*, so if this is adjustable, you can make the motor run in either direction. If you find that both ends touch, the crank will need to be shortened
On my LTD motor one end of the displacer cylinder (piece of 6" plastic drain pipe) is glued to the cold plate, an O-ring is glued to the other end, and that bears on the hot plate, that way I can open the chamber by undoing 12 x 5 mm nylon screws.
Ian S C

Ian,

Thanks for the reply! Good advice. Now that we've looked at the con rod, we've noticed that the pin that connects the con rod to the crankshaft is not 90 degrees. It looks like it is pitched out, thus making the distance along the crankshaft from the axel to the con rod larger than specified, and thus lengthening the displacer throw. So, that'll get fixed first. Also, good idea to the bottom being glued to the displacer ring. One less thing to have to worry about.

Mosa