Piston question for stirling engine

[dnp101677]

I am working on an engine that I am missing some plans for and I cannot figure out what the counter bore is for. The only thing I can think is that there is supposed to be some kind of nut that I am supposed to make that I, again, don't have the plans for. Does someone know how this piston attaches to the displacer rod? I think I may have it on backwards in the picture.

Thank you,

Dan

 

[vlmarshall]

Is the displacer piston made of a difficult-to-thread material? Perhaps it's something brittle, like graphite. In that case, my guess would be that the insert is a threaded reinforcement to attach to the displacer rod, and that you have it backwards in the picture.

 

[Stan]

There is no dimension on the depth of the counterbore but looks to be less than .1" so probably just clearance for the end of the bushing screwed into the end of the cylinder.

 

[vlmarshall]

...probably just clearance for the end of the bushing screwed into the end of the cylinder.

Ah, yeah I didn't think of that possibility.
Although, scaling the drawing, that counterbore is about .115" as drawn, and the through-hole .105" . Also notice both bores are not threaded, which is why I assumed the "missing part" must have the threads. ;D

 

[Stan]

Vernon: The piston rod is likely threaded into the piston and the counterbore may provide clearance for a locknut but it could also be held in with Locktite. The bushing however is the most critical part of a Stirling. It has to screw into the end of the cylinder and make an airtight seal and then the piston rod has to polished to get the least friction and best seal between the rod and the bushing bore.

A Stirling is never a source of power. It is difficult getting it to produce enough power to keep it running. HTH Stan

 

[dnp101677]

The print calls for aluminum material. And the displacer rod is threaded into the piston. I was kind of thinking there was supposed to be an insert too. Only I was thinking more along the lines of a machined insert - kind of like a female screw, if you will. The female screw could have a slit cut in the end for a regular screw driver. This way the displacer rod could be tightly fastened. I think either way I have the piston backwards. I would appreciate anyones thoughts on my insert idea. I don't have a CAD system on this PC so MS paint is all I have the portray what I am thinking. The picture would be a side view of the insert.

I just don't know if this is even necessary. The displacer rod has a 5-40 thread so, can I find a nut that is thin enough for the .125 deep .625 dia. counterbore? I don't know, maybe I am over thinking this thing. All I need to do is fasten the displacer rod to the piston and make sure the piston is facing the right way.

Thanks again! You guys are great.

Dan

 

[dnp101677]

Sorry, here are the piston dimensions.

Dan

 

[shred]

There's not a skinny little gland that fits into that space during operation? That looks a lot like the crank end of the displacer piston on one of mine-- it has a long gland to keep leakage down.

 

[rleete]

Is there a set of notes to go with the plans? That "A" in the circle is a notation, either for the mating part or a fit.

 

[vlmarshall]

Is there a set of notes to go with the plans? That "A" in the circle is a notation, either for the mating part or a fit.

It's a notation for the cross-sectional view made on the other half of the drawing. ;D

 

[dnp101677]

Sorry, I cut that part off when I took the screen shot. It's actually a revision mark for when they removed the 45 degree chamber from the c'bore. I will just attach the whole print this time. So, I guess I do have piston backwards in the first picture I am showing (the SW assembly pic). I just don't' know if I should make an insert or just deviate from the print and make a c'bore for a locknut.



View attachment 3016 Displacer Piston.doc

View attachment 3016 Displacer Piston.doc

 

[idahoan]

The drawing I have doesn't have a lock nut; the piston just screws onto the displacer rod. You had it assembled correctly in the first picture. I think the counterbore is just clearance for the displacer gland. Although I'm not sure why the dia. needs to be so large. This piston is just the end cap the rest of the displacer piston is a section of lighter fluid can cut to length and pressed on to the cap.

I hope this helps.

Dave