walking beam engine does not run

[lasanderson]

I built a walking beam engine from boydhouse.com online plans and timed it as was said. The piston was made from JB Weld and is made like the Haige type. All the parts move very freely. I use Sterno for the fuel.
Everything looks correct but It will not run. It doesn't even try to run.
So where do I go from here? I built a different type of stirling engine which runs great but this one has me puzzled.

Hope you can help.
Thanks

[jimlarsen]

Post some pictures or a video and I am sure you will get lots of feedback. It really helps us to see it.

[vile_fly]

There seems to be an "update" to the tin can walking beam engine. The displacer piston rod has a 90 degree bend in it to keep the displacer piston from falling off of it during overheat conditions. Hopefully, the displacer piston is sealed up well enough to be submerged in water without leaking. If the displacer is not sealed, then you have alot of dead-airspace that will prevent it from developing enough energy to run.

[lasanderson]

Yes I saw that modification with the bend in the rod. I soldered both ends of the can at the rod. I also soldered the top of the displacer piston can. I can see the displacer moving thought the piston hole. But you have to wonder just how hot it is inside the power cyclinder. I might be hot enougt to melt 50/50 solder. I checked for air leeks on the power cyclinder. I found a very small amount around the rod fitting an sealed it. The only leek that might seem to be a problem is the fitting that the displacer rod enters the power cyclinder. I just don't see how I can make that tighter without adding friction.

[jimlarsen]

Are you cooling it with ice? Ice water? How much of a temperature differential do you have?

[lasanderson]

No, I haven't tried that. How much differential do you need for this engine? My other engine does not have a cooling on it. I use a small candle. It runs fine untill the engine is all the same temperature and then it stops.

[jimlarsen]

Try cooling with ice. Increasing the temperature differential is usually beneficial.

[lasanderson]

I just tried ice water and it made no difference. One thing I did notice was smoke bypassing the piston and also a small amount exiting the displacer rod bearing. The piston and the cyclinder are correctly sized according to the plans. So I'm still puzzled.

[jimlarsen]

That sounds like a pressure leak.

Smoke coming from the inside? That can't be good.

In an ideal setup you should be able to feel compression on your piston. This is tested by disconnecting the piston from the flywheel to remove all load. Press it in or pull it out and then release it. It should spring back a little as a result of the air pressure. if you don't get any pushback on your piston you have too much pressure leaking or too much friction.

Some small leaking is necessary, but too much will cause it to stop working.

Another test you can do also requires the piston to be disconnected from the flywheel. Light the candle and bring the engine up to operating temperature. Manually move the displacer and watch the piston. You should be able to get the piston to move in and out by manipulating the displacer. If the piston does not move in this zero-load state, you have a problem.

Sometimes a pressure leak around the displacer pushrod can be fixed by applying a drop of light oil. Oiling the piston may help too.

[Junkie]

I always disconnect the displacer and move it by hand. You can then feel/see the movement on the power piston. If there's non, there must be a big air leak somewhere.

[Administrator]

lasanderson,

I sent you an email.

I will post a sheet here on how to trouble shoot the engine when I get home. It is probably a timing issue.

Darryl

[Administrator]

These engines are very fussy about friction. That is, all the joints and moving part have to be "loose", very loose. If the parts fit too tight, it will not work. This is the reason most of the engines don't work right off. Make it loose (but not sloppy). The power piston and piston cylinder need to be close, but not tight. It needs to be able to transfer the power without dragging, but tight enough to not leak down the sides. Oil the heck out of all the joint and the inside of the power piston cylinder and the rod going into the displacer with something like WD40 or a very light oil. Don't use heavy oil ! A lot of people have built this engine and email me with the same problem. It will work if built to specs.


What kind of heat source are you using?

When heated up, turn the flywheel in a counter clockwise direction (this is the direction it runs). Can you feel a “push” as the flywheel goes around? Or maybe a “pull” as it comes around? If so and it won’t run it is a “timing issue” The rods are slightly off dimention. It does not take much at all and it seems like some are fussier that others. You can try bending the rod that goes from the flywheel to the walking bead slightly and check it again.

Remember, this engine will not start on it’s own. When heating you have to give it a little turn counter clock wise to get it to start.

If it stop right away there is another problem. If it seems to coast a little before stopping, it is probably a timing issue.

Most of the time they run for the first time right off the bat. But every once in a while one wants to be stubborn!


Stirling engine test:

You can tell how much pressure you are building (or vacuum) in the displacer cylinder by doing this test

Remove the power piston connection rod. (the rod from the power piston to the flywheel) and let it just hang.

Place the power piston in the center of the power piston cylinder (half way).

“Rock” the walking beam to where the left side is down (displacer is in the lower position)

What we are going to do here is light the fire under the engine and after a short time “Rock” the walking beam where the left side is “UP” (displacer is in the upper position). This will immediately start to heat up the air in the displacer cylinder and build pressure. This will push the power piston outwards.

Immediately “Rock” the walking beam on the left side down and the air will cool in the displacer. This will create a vacuum in the displacer cylinder and that should pull the power piston back into the power cylinder.

If your power piston is not moving back and forth, you have a problem. If it is moving back and forth then you have a timing issue or too much friction. Or too much weight on the flywheel or somewhere.

If the problem is the power piston is not moving, then you have either a leak in the displacer cylinder or power cylinder, or your piston is too loose and the pressures are blowing by the sides of the piston. Another possible problem (less likely) is your piston is too tight. It should move very freely in the cylinder.

[lasanderson]

Well it finally runs! After reading the the trouble shooting paper you sent me. I made a new piston of JB weld that has a closer tolerance. However I did not use the Haige Type. Having a pivit joint so far back from the center of the piston didn't seen right. The piston has to fit tight enough to seal but not create friction. The pivit point that far back was causing the piston to twist in the cyclinder. So I made the new one like the plans original show. That picture was a rear wheel cyclinder piston. JB weld is a hard epoxy but is easly worked. Once the epoxy cured I center drilled the middle of the piston and crossed drilled for a wrist pin. This piston now looks like any other and seals well.
The only problem now is the displacer piston bearing / seal on top of the power cyclinder. If I do not keep lubricating it starts to leek pressure. You can hear it. It makes a slurping sound and the engine starts to slow down. It will stop if I don"t add oil. Once I do the bearing seals and the engine picks up speed. I would like to find a fix for that so that oil does not get down in the power cyclinder. It smells.
So I guess I'll keep tweeking until Its perfect.
Again thanks for the help.

[Deepwater]

Just completed my first Tin Can Stirling as per plans. Ran fine @ about 60 rpm.
Made the small 1 1/2" long linkage which joins Displacer rod to Walking Beam, from 1/8 aluminum strip with several adjusting holes. Found linkage dimensions per plans to be spot on. Set displacer timing per plans.
Removed displacer and made a regenerator from roll of aluminum screen door material approx 4" long x 6 ft.long and wound and attached to outside surface of displacer. using ss wire and a little JB to prevent selvage edge from unrolling. The displacer can lip is slightly smaller than the can bore, so the regenerator has to go through that opening!!!!!

That little rascal romps along @ several hundred rpm. Lost count at 250rpm since I was using only manual count and a clock second hand.
No sign of overheating the cool water end. Noticed it takes a while to run down after heat is removed.
Very happy,... ready to move on to my next Stirling project..

[Administrator]

Very happy,... ready to move on to my next Stirling project..

See, that is why I have the plans there. I love hearing that. The little engine is a great learning device and is a great prep for a "more challenging" model.

Have fun!

Darryl