Stirling Engine H8101 Grizzly

[ROBERT BLACKSHAWParticipant @robertblackshaw40066]

Hello, as I have now made most of the parts for the Stirling Engine H8101 from the drawings on the Grizzly web site, I need the dimensions for the hot cap which are not shown.

I contacted Grizzly and asked to purchase the part, but a minimum of $200 and a minimum 70lb shipping weight. I also asked the technical department if I could have the dimensions but they refused. They suggested if I knew someone in the USA they could post the part to me.

I understand that the dimensions for hot and cooling pistons are important, I have made the 13mm cooling cylinder and piston. If anybody has the dimensions for this hot cap it will be much appreciated.

Thanks for any replies

[ROBERT BLACKSHAWParticipant @robertblackshaw40066]

[HopperParticipant @hopper]

If you know the stroke, you can probably work it out by looking at other designs. From memory, swept volume (stroke x piston diam.) of the displacer piston is about 1.5 times the swept volume of the power piston. Some engines go as low as 1.2, others as high as 2.0. But it seems 1.5 is a good rule of thumb. You then need to make the cylinder to have 20 to 40 thou (half to one mm) clearance between piston and cylinder bore and about the same between piston and the end of the cylinder at each end of the stroke.

Otherwise, if you want to buy Grizzly's hot cap, there are numerous mail forwarding agencies in the US who charge basic air freight plus a small service fee. Still not cheap, as US postal prices have gone stupid high recently, but you would certainly get a lot of change from $200! If you google "mail forwarding agencies USA" you will find some good options.

Edited By Hopper on 17/05/2016 02:19:40

[Ian S CParticipant @iansc]

Robert, I had a look on line at the plans, I think they omit the hot cap dimensions to make it difficult to build without the bought kit. The OD of the displacer cylinder is 18 mm, so the internal diameter maybe some where near 17 mm, leave a gap of 1 mm gives you a diameter of 15 mm. The length of the displacer should be 3times the diameter, so about 45 mm long. I don’t know the stroke, so you need to work that out (2 x the throw of the crank), add a couple of mm to give the clearance at each end, and you have the size.
Ian S C

[Ketan SwaliParticipant @ketanswali79440]

If SIEG HAE01 kit, then try this:

HAE01-Part 21:

————————————————————————-

HAE01-Part 45:

[Ian S CParticipant @iansc]

Robert, ifall else fails, for the displacer you would get away with using the steel casing of a size AA Nicad battery. It is only 14 mm diameter x 45 mm long, one of my motors uses one for the displacer, and another uses one for the hot cap.
Ian S C

[ROBERT BLACKSHAWParticipant @robertblackshaw40066]

Thanks for your replies on this, I didn't really have clue on the displacer piston being 1mm smaller than the cylinder. It seems obvious now, hot air moved to cooling power piston creating the vacuum.

Can the displacer piston be made out of solid brass, as the drawing shows it being hollow. I have made the power piston out of aluminum as well as the cylinder if thats correct.

[HopperParticipant @hopper]

It is best to make the displacer piston hollow but sealed. That way it conducts less heat from the hot end to the cold end of the displacer cylinder. Stainless steel is a common choice because of its poor conducting properties.

Aluminium on aluminium for the power piston/cyl is not the greatest combo either for friction or wear. I would think about making the cylinder from steel and the piston from ally, or even vice versa. Or brass for one and steel for the other. A popular choice though is a cast iron piston in a steel cylinder, or vice versa. Lowest friction option would be a graphite piston in steel cylinder, but graphite is 'orrible messy stuff to machine.

[Ian S CParticipant @iansc]

If I were building this motor I would still use tha aluminium power cylinder, BUT I would bore it out larger to take a steel liner, and I would make a cast iron piston. One of the most important things with these motors is the reduction of all points of friction, so knowing which materials work best as low friction bearing surfaces is a major part in designing them, this knowledge can then be carried on to design future models, steam, IC, or even another hot air engine.
Ian S C

[ROBERT BLACKSHAWParticipant @robertblackshaw40066]

With advice given I have decided to make remake the power cylinder with a steel liner and cast iron piston. The drawing and advice given shows a sealed displacer piston. I was to put a minimum vent hole in this as I thought of expansion when hot, am I correct or not. I am grateful for these replies as my questions must seem rather basic as to question on this forum.

[Ketan SwaliParticipant @ketanswali79440]

I dont know enough about the subject, but I do know that the displacer piston needs to be light. Generally these systems work well when things are light, and, to the best of my knowlege, avoid putting in a vent hole.

Perhaps invest in this book for guidance. Roy Darlington – Author of the book is a great authority on the subject, along with the members of the Stirling Engines Society.

I am sure that the Society will have a stand at the Doncaster Show over the weekend. If you can make it there, I am sure that members of the society will be a great source of information and guidance.

Ketan at ARC.

[Ian S CParticipant @iansc]

NO, no holes allowed, it will be ok and the aluminium plug in the cold end that the rod screws into can be held in place with shaft lock Loctite. I’m not entirely correct in saying no leaks, you can use a bit of tube for the displacer rod, there by venting the interior to atmophere, I’v done this on some of my engines.
Ian S C

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