model does not run

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model does not run

Postby jnt1 » Mon Sep 17, 2007 6:55 pm

I machined and assembled a Stirling engine model
(http://www.grizzly.com/products/H8102/images)
It will not run and the seller has no answers. Where cam I get help?
Jason
IL, USA
jnt1@paa-inc.com
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Response to model does not run

Postby iron_goober » Tue Sep 25, 2007 6:04 am

Jason,

If you give the flywheel a quick spin with a flick of the wrist, it should rotate about 4 to 5 revolutions before stopping, if it does not the engine probably has too much friction to run.

Also check the engine for leaks, any small leaks can completely stop an engine, one way to do this(if you don't mind disassembling it again to let it dry out if there is a leak) is to bring the power piston all the way up to TDC, and then dunk the whole engine under water, and then push the piston down to BDC and see if there are any air bubbles...if there are, you need to fix the leak.

Those are the two most common problems with engines.

Also, have you tried using a propane torch or something on the engine to get it REALLY hot to see if it will run? Sometimes getting it cherry red will overcome any friction or leaks, but of course, you always have to get it this hot to run it..and that isn't as fun as running it off a candle or small flame.

Anyways there are a few ideas...see what you can find and repost if
you can't get it to run.

John
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Response to model does not run

Postby iron_goober » Tue Sep 25, 2007 3:31 pm

Also, I found this comment on the website..be sure to do this between the power piston cylinder and the displacer cylinder.

"The finished kit measures 9-1/2"L x 4"W x 6-1/2"H and the base measures 12-1/4"L x 6-3/8"W. YOU WILL NEED TO DRILL A SMALL 30° HOLE BETWEEN TWO CYLINDERS FOR PROPER OPERATION."

You might have already done this...but just in case...

John
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Response to model does not run

Postby johnemack » Wed Sep 26, 2007 8:08 am

Hi Jason,

Any success, yet?

Because the power of small hot air engines is so tiny (most of them just go, without ever driving anything), I have had to a) minimize friction and leakage, b) use a high temperature and good cooling, c) use a heavy-enough flywheel and get the balance right. Others will have advised of those, no doubt.

You are using metal pistons in metal cylinders, I think. Are they oiled? Although that might help to seal and reduce static friction, viscous drag increases with speed. Are there any eccentricities or offset forces that are increasing the side loading unnecessarily?

If your horizontal piston is heavy, it could be causing sliding friction (you do not need much!). I have found graphite pistons to be the best so far, especially when lapped, because of their low dry-friction (at any temperature), light weight and low expansion (so leakage and binding are constant, unlike with low-friction plastic pistons). Since the forces are also tiny, your metal piston could be foil thin to save weight.

One snag with a heavy flywheel is its bearing friction. On very small LTD engines I have found the drag of sealed-for-life small ball bearings to be greater than that of small plain shafts, so I use the thinnest wire crankshaft that will just carry the flywheel. (True the friction is the same but the radius at which it acts is then smaller.) Would smaller shafts help with your engine?

Good luck with all your experiments! You have a nice looking engine, there, and you will soon get it running, if not already. I bet you then carry on experimenting to make it run better. Everybody does, but that takes longer than making it in the first place!
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