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Resurrecting A Jensen 20g Toy Steam Engine

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DoogieB

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I've been collecting Jensen model steam engines for a several years now. It's a no-brainer for me. They are great toys, extremely well built and made right here in my home state of Pennsylvania.

While it's cool to find the mint condition examples, I actually prefer finding a nice fixer-upper as that way I can make it my own and make something old new again.

A few years ago I got a great deal on this engine on Ebay. Typo in the auction title and the somewhat grubby appearance really knocked the price down. Auctions are always a gamble, but let's look at the engine as I received it.

jensen20_1.jpg


jensen20_2.jpg

The Good:
  • It's a Jensen 20: a powerful, electrically-heated toy steam engine. A classic Tom Jensen design.
  • Cast-iron based generator, which are now getting quite pricey.
  • The boiler looks in great shape: no dents, stripped threads or other signs of abuse.
  • It's dirty, but not rusty.
  • Upon opening the box, got a good whiff of the distinctive smell of 3-in-1 oil. At one time, someone cared about this engine.
The Bad:
  • The frame below the boiler it's stained black. Definitely had some leaking gaskets and leaking water is hard on the heating element (the bottom of boiler sits on a curved heater).
  • General dirty, stained appearance
  • Found out later that the valve chest needed a re-solder
The Ugly:
  • The power cord was cut in half and reassembled by twisting the wires together with some black tape. Yikes!
The Weird:
  • The generator is actually at the wrong spot as it needs to be run off the main flywheel to hit the proper RPMS. I believe this was a factory 20 and someone added a generator later on.
None of these problems was really a big deal for me and I was quite happy with my purchase.

Fast-forward some time and I finally decided to get moving on this project. Jensen is happy to sell you parts and the extremely long production runs for their products means they usually have what you want. I actually didn't need that much stuff as I made my own gaskets from PTFE gasket martial, although I did get a new name plate and a few other small items.

jensen20_3.jpg

And here it is all cleaned-up and running like a champ. I'm very pleased with the performance of this engine and even with all the engines I have it's already my favorite.

I still have a bit more tweaking to do until I'm satisfied but the 90 degree plus weather we are having isn't exactly conducive for playing with live steam toys. I might have to put in the box for a bit until late summer/early fall, but I'll try to get a short video up of it running before that. I've already made a pressure-gauge attachment.

You know, it's kinda funny. Making drive pulleys for these steam engines was the original reason I started looking into metal working equipment. At that time I was looking at one of those very small lathes, so I started watching MrPete's videos to see what it was all about. Well, that certainly took on a life of it's own. :) After a few years I ended-up with a South Bend 10K lathe, a bandsaw, belt sander, a mill, a bunch of tooling, etc-roo and etc-raa.

And I still haven't made any of those pulleys yet! :)
 
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T Bredehoft

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Nice job, I made a couple of steam engines early on, in the '70s, never really got into it.

The generator runs the light bulb, could another, (bigger) generator run the heater? Get it up to speed and throw the switch, it's self sustaining..... Just wondering.
 

cjtoombs

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Nice job, I made a couple of steam engines early on, in the '70s, never really got into it.

The generator runs the light bulb, could another, (bigger) generator run the heater? Get it up to speed and throw the switch, it's self sustaining..... Just wondering.

As mentioned above it would violate the laws of thermodynamics. The laws are:


1. You can't get ahead, conservation of energy.

2. You can't break even, entropy (basically disorder) increases in a closed system.

3. You can break even, but only in a pure crystalline substance at absolute zero, which can't be attained.


What you described is a perpetual motion machine which law 2 says is impossible and law 3 backpedals on a bit and says it is possible, but only under impossible conditions. If one were to hook the generator to the heating element and then put enough energy in to get everything going, it would spin down based on loss of that energy to the surrounding air through heat dissipation both directly and through friction generated heat. With the efficiency of that little motor, generator and boiler you would probably have to have instrumentation just to determine the difference between having the generator connected to the boiler and not connected.
 

T Bredehoft

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Just for fun, I'm aware that you can't get ahead, If only....I remember hearing somewhere that steam engines were 17% efficient. lots of loss there. For 100 energy units you put into the boiler, you get out 17. Such a waste.
 

cjtoombs

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I've heard about that for reciprocating steam engines. I think some of the most modern power plants can get close to 50%, but they are pretty exotic (and expensive). The steam engines of the day got by because the fuel they used was very cheap, so efficiency didn't matter much. I've heard it was the maintenance costs that drove transportation to diesel, not so much the fuel costs.
 
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