IndianaRog and the Temple of Steam

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Jensen 51 Replica

The steam power plant pictured above is a 2006 restoration and conversion of a 1967 vintage Jensen Model 50 engine into an enhanced replica of a Model 51 power plant, Jensen's top of the line flagship steam engine.  I have dubbed it 51R001 (now that I have built a 2nd for a friend).  

I have operated it now for 13 years (335 hours on the Hobbs meter) as of this 2019 edit.

Basic features

The heart of the Jensen Model 51 replica is the Model 50 engine/boiler combination that drives it.  The 50's re-nickeled boiler seen below absolutely gleams compared to how it looked upon receipt.  That boiler is 5 inches in diameter x 10 inches in length and made of heavy gauge brass beneath the nickel finish.

In the 50 > 51 conversion process, a condensate/exhaust stack with brass drain line is added as seen not only works well, it sounds pretty cool and sends a large column of steam straight up ! The light green engine base as well as the generator bases are made of heavy cast iron...built like an Abrams tank! 

The cylinder of the Model 50 engine has a 1 inch bore and the piston travels a 1.25 inch stroke.  It is said to create 1/25 horsepower.  The nickel plated, cast iron flywheel is 5 inches in diameter and smooths out the operation of the entire power plant with it's strong momentum.

The governor is both functional and adjustable.  It will begin reducing steam at a designated speed triggered by the rising arms of the governor which turns a steam reducing valve.

The master steam valve (upper round black knob) enables user to throttle things down to a snails pace if desired or let it rip full speed.  The other black knob on the boiler's face allows for complete boiler draining or reducing water level during operation if it has risen too high. 

The eccentric operated feedwater pump can be seen to the left rear of the photo below.  This simple pump can maintain and even gain on the water level in the boiler, consuming feedwater at a rate of 1 gallon in 90 minutes of operation.  Water is supplied to the pump from a functional 30 inch tall water tower and tank.

In photos above and below, you can see the dual open window cross head guide supporting the piston rod as it enters the cylinder.  Also visible are the slide valve and governor linkages.   The Jensen 50 at the core of this setup was built to last...52 years and counting as of this 2019 edit.

Jensen 50 and 51 Background Info.

The Model 51 and the Model 50 at it's core, are huge by toy steam standards and really more closely fit in the machinist built model category, with each getting lots of TLC as they are individually assembled.  

As compared to a standard Jensen Model 50, the factory built 51 adds a functional water tower, a console with 115 volt AC, low voltage AC and low voltage DC switches and analog gauges.  In addition, the 51 adds a unique combination AC/DC generator capable of making low voltage AC to power the single lamp post or DC to power the small DC motor with mounted saw blade for visual effect. 

A working condensate exhaust stack and larger base board complete the original 51...all 75 pounds worth!  I know of only ONE website on the internet where you can see photos of a factory built Jensen 51:  The Steam Gallery...for additional technical detail not covered here or on Jensen's own website, visit The Steam Gallery. 

Jensen discontinued making both the 50 and 51 models in 1996.  Fortunately, they resumed manufacture of the Jensen 50 in 2016 and this model is once again listed on their website for $5,000.  I'm not aware of any plans to re-introduce the 51.

The Model 51 pictured to the right, "was" featured on the Jensen website for many years, though it was a placeholder only.  The Model 51 pictured below was from a 1993 advertising brochure.

A steamer interested in acquiring either an early 50 or any 51 must scour eBay and/or let it be known on the steam "grapevine" that they are seriously looking for one.  Few collectors are willing to part with one of these jewels, but occasionally circumstances change and another steward takes over the reign of ownership.

In total Jensen made between 250 and 300 Jensen 50's.  It is believed about  27 of those were further developed by Jensen into the Model 51. 
As of 2014...I'm aware of seven private collectors who are in possession of several flavors of the "51":
  • the original "prototype 51" built in 1977
  • four Jensen built "production 51's" (one of them was just found in 2013 by a new collector)
  • the last iteration Jensen made, dubbed a "50 1/2" by it's owner (unique in that it was built by Jensen with a water tower, but no console)
  • two enhanced "replica 51's" built by me (my first and last!
The location of the remaining 51's is a mystery...I welcome any additional information to update this list. 

For Jensen 50 and 51 owners, history buffs or those just interested in the many variations of these two models from their inception, the tab entitled "Jensen Chronology & Varieties" was put together by two of the most knowledgeable Jensen collectors in the world...Bill Wheeler and Gil Garceau.  These gentlemen have graciously allowed me to post it on this website.

My original Jensen 50 used as the basis for this project appears to be a transition piece between Type 4 and Type 5 noted in this document, having some of the former and some of the later's features.  This is not uncommon for Jensen as Tom Sr. would frequently experiment and the results of those efforts brought about the next variation in a long progression.

Jensen 51 Prototype

Pictured below is the original 1977 prototype built by Randy Calhoun that was the inspiration for the 27 production 51's that followed (photo courtesy of Jensen Online Museum).  Notice how this initial version actually sported 5 lamps and two Jensen #15 AC generators in a one of a kind orientation.  DC generation was not part of the prototype.

The prototype once went for a continous duration of operation record, surpassing 8,000 hours, sheparded by a group of college engineering students in rotating shifts.  I have seen this prototype in person at Randy's home...the Hobbs meter does indeed bear witness to a very, very long run and the durability of the Jensen 50 at it's core.

Randy's 1977 prototype for the entire Model 51 design was put into production with several changes to simplify it, but the general concept was carried through as he envisioned it.  The first three production Jensen 51's featured AC voltage generation only from a pair of Jensen 15 AC generators oriented like I have done with my rendition. 

After the first three production examples, the paired AC generators were replaced with a single combination AC/DC generator supporting one AC lamp, one DC motor and a console of control switches and analog gauges. 

My Jensen 50 restoration and conversion into a Model 51 replica (and then some!)

What follows is as much to document it for my own satisfaction as well as for the curiosity of other steamers.  I didn't replicate perfectly as parts availability was a roadblock for some components, but I got the "look" and functionality close enough for government work and in my opinion I improved on the least in the fun dept.!

As luck or good Karma would have it, in February 2006 I found a Jensen 50 for sale on eBay.  It looked to be of late 1960's vintage and as the story goes it was the demonstrator once used by a Jensen sales rep. in the Western U.S.   I didn't hesitate to buy, despite some obvious corrosion visible in the pics, especially on the boiler face. 

Here is how my Jensen 50 looked upon receipt in Feb. 2006:

Despite being a little rough, it WAS a Jensen 50, so it was exceptionally rare in it's own right.  This one came packed in Sept. 1967 vintage newspapers from Jeannette, PA, that and it's features make it a good bet it was built about that time.  

My newly acquired Jensen 50 was complete with no irreversible damage and came with it's original corrogated box as well as a sturdy wooden outer shipping crate.  It also ran quite well upon firing it up, although it leaked profusely at the usual gaskets. 

Click here for more "on arrival" pics

On the negative side, much of the nickel finish was corroded, especially the face of the boiler.  Painted parts and wood I could refinish, but I felt the boiler and several other nickel plated parts needed to be professionally replated. 

So, after operating it a few times, I tore it completely apart and sent select parts off to a nickel replater for a 9 week turnaround.  It felt a bit like sending the Shroud of Turin out to the dry cleaners, but I was very pleased with their work upon it's return. 

While waiting for re-plating to be finished, I got to wondering what it would take to restore and convert this engine into a working replica of a Jensen 51?  

I was soon on a quest to build the 28th Jensen 51, (at least a decent replica of one).  Being of 1967 vintage, my boiler is the older flat faced type with a built in stay rod running end to end.  Mine was made about 10 years before Randy's 1977 prototype, which bore the later rounded style boiler face...none the less it lent itself well to conversion.

Replication into a reasonable facsimile was possible after several Jensen 51 owners kindly shared photos of their examples...I'm very thankful for their help.  Those photos gave me a rough idea for how to move forward and for most of the fabrication they were my only plans, no measurements per se.  

The initial project spanned 10 months almost to the day, from receipt of my Jensen 50 until I finished the initial restoration/conversion and first steamed it on Dec. 19, 2006, a nice Christmas present indeed.  Much of that time span was spent searching for parts to build it.  After the initial completion, I continued to modify it and enhance it's capabilities to what you see in these photos.

It's 2019 as of this writing and I believe I have finally enhanced it all I can...she's finished!!! Then again......

Click here for "progressive restoration & construction pics"

To get a perspective of the size of the Jensen 51, here it is next to a Jensen #25 cast iron type engine. 

All factory Jensen 51's bore a custom owner's logo on the water tank, often that of a power co. or university that used these pieces for display and teaching. 

I came up with a logo of my own that was reminiscent of a Jensen logo, but clearly indicating it was a replica. 


The console required learning how to operate a router to mimic the edge design of the box used on the originals. I eventually figured it out, but I went thru a fair bit of wood doing so!

Below you can see the console with it's full complement of 20 switches, gauges, a fuse and a pilot light wired into the front. Building and wiring such a thing is not for the faint of heart!

Finding the same style analog Shurite and Hobbs brand gauges that graced the original Jensen 51's took months to track down from multiple internet surplus sources, as all but the Hobbs hour meter are now out of production.

The biggest challenge of the entire project was wiring up the console, a major hurdle for the electrically challenged like me, but very satisfying to finally figure out how to wire it correctly.  There is the 110 Volt AC incoming power you don't want to mess up, and then the separate low voltage AC and DC circuits. 

The console IS correct, safe and it works as intended, but it gave me fits to say the least.  

The rear of the console seen below, sports a master switch and fuse that control all line voltage, a rotary dimmer switch for more gradual control of one 660 W heater, a switch to route DC power to external accessories if desired and a small computer fan that prevents heat buildup inside the console if that were to occur.

All line wiring, switches and the fuse were upgraded to handle the higher electrical demands of the newer heaters given original setup was labeled as 900 watts and this one is over 1600 watts at full power.

I now have greater respect for the creativity of Engineer Randy Calhoun, who in 1977 perfected the console concept for Jensen and helped build every production Jensen 51 made.

To correctly reflect the "souped up" heaters installed in this project, friend Mike Philips gave me a new Jensen ID plaque upgraded accordingly:

HAPPY below was taken while steaming on Jan 29, 2014 and shows the 250th anniversary (in hours of operation) for my Jensen 51 Replica. 

This is the cumulative run time since initial restoration and conversion from a 50 to a 51 replica in Dec. cool is that !!!   I need another photo as I now have 335 hours on this meter (Jan 2019).

Photo was taken by the light of the console lamp alone, as it was steaming and generating light while I took the picture.


Although the wood base on my original Jensen 50 was in good shape, I opted to go with 100% new wood seen below.
I used furniture grade 3/4 inch thick oak plywood for the bases, a bit better grade than the originals received.

Wood was stained and given five coats of hand rubbed polyurethane to ensure protection from the inevitable water, steam and oil exposure.  I think it turned out nicer than our dining room table!  The console sides were made of pine with a 1/2 inch thick birch plywood top portion. 

The following photo shows the whole plant turned around to show the rear...looks good either way, but I'm biased!

Lights, motor and generators

Three of the 5 lamp posts used were the tall type Jensen made for the Jensen 51's, the other two used smaller Jensen lamp posts friction fit on extensions made from large scale stainless steel veterinary needles used on cattle.

A factory Jensen 51 has the DC motor mounted in a more hidden location close to the rear of the firebox atop a piece of metal tubing.  I wanted mine in a more visible location, yet I was somewhat limited for real estate.  I chose to mount the DC motor up on a little wooden pedestal of it's own as seen lower right.

The DC motor (courtesy of steam friend Mooseman), was extracted from it's plastic Meccano housing and then epoxied inside a tube of aluminum, cut from the body of a permanent marker pen.

The motor with it's aluminum "jacket" was then epoxied inside a nice brass mount found on eBay. 
In lieu of a Jensen style silver saw blade for the motor, I mounted a Jensen line shaft pulley instead, painted red to match the flywheel and generators. 

The lamp sprouting from the AC generator closest to the DC motor (see photo to the right) is more sleight of hand than it first appears.  It shines on the DC motor/pulley and is activated whenever the motor is turned on.

While it looks like it's an AC lamp coming out of the #15 AC generator, in reality it's powered by DC and is insulated from the AC generator base by a rubber sleeve...the location for that lamp was perfect, but I wanted to tap my ample DC power as the motor spooled up.  It works perfectly!

You simply can't find a combo AC/DC generator of the type used on Jensen 51's and the equally rare Jensen 15D accessory set, as they were custom made by Jensen as each 51 or 15D was assembled. 

Before Jensen came up with their single unit/combo AC/DC generator used on most of the 51's, the first three 51 examples were AC only and used a pair of model #15 AC generators tied together by a spring belt in a layout similar to what you see here. 

The prototype seen earlier in this writeup also used two AC generators, but they were oriented differently.  The layout seen here has worked very well for me and generates substantial light.

The following is a nighttime photo of the 51 replica illuminated only by the AC and DC light it generates.  Odd as it may sound, I often run it this way without room light...a bit like sitting by a campfire!

To improve traction between the main flywheel and the triple pulley driving the three generator load, I ran a double set of 2 mm green rubber belts to either side of a 2 mm green rubber belt that runs down to the DC generator beneath.  This setup works very well and was inspired by a two belt configuration seen on the pic of a Corliss engine that headlines this website.  

The generator armatures are oriented in phase and wired in parallel, enabling them to support more lamps than the original, solo AC/DC generator on a factory Jensen 51 could handle.

If you have to substitute, you might as well make an improvement at the same time !

To supply DC power, a small, modern "stepper" motor from a defunct computer printer was used, turning in reverse to generate DC power.  Given that the "stepper" motor was square and ugly looking,  I discretely concealed it within a raised wood platform beneath the paired AC generators (photo to the right).

The DC generator pulley is tethered by the light green rubber belt to the center step of the triple pulley above it.  This setup works beautifully and powered by this engine, it will generate up to 24 volts of DC power under full pressure/no load conditions.

The belts discolor a bit with age and exposure to oil, hence the minor color differences seen in the photos...but as of 2019 they belts have over 195 hours of operation on them without issue (I went to the green rubber belts at 140 hours as the spring type were wearing the aluminum triple pulley into an oblong shape).  A good friend from Australia, known in the steam community as "OzSteamDemon", custom machined a new, solid, triple groove pulley for me, which I mounted at about 140 hours on the Hobbs meter. 

As of Jan 2019, the newly machined triple pulley has 195 hours on it and it continues to work flawlessly.  Thanks Geoff!!

At the same time, I switched from the steel spring type to custom fit, green rubber belts seen above to stop further pulley wear.  I also found an unexpected benefit of less resistance and more rpm's using this type of win!

While I was at it, I also switched to a 2 mm green belt to power the governor and likewise picked up a few more rpms.  I believe the green belting provides the grip needed to avoid slippage without the tension (drag) imposed by spring belts. 

This type of belting remains "grippy" even if oil gets on it, which invariably happens.

Like the generator issue, I had to work with different immersion heaters.  The original 300 watt immersion rod heaters are no longer made today, replaced with 660 watt versions. 

I kept one good condition original 300 watt rod and added two NEW 660 watt rods plus the ability to dim down one 660 watt rod via the rotary dimmer.

Using a dimmer on one heater enables control of amperage down to the single amp...very nice for maintaining boiler pressure at a desired 24-26 PSI.  I have found 24-26 PSI to be a sweet spot where there is ample power generation and the feed-water pump can keep up with boiler make up water requirements.

Since I had ample DC generator power I also added a pair of banana jacks to the edge of the base, allowing DC electrical power takeoff of sorts.  The jacks are discretely installed to the right rear of the console as seen in photo to the left. 

With the flick of a rear mounted console switch, DC power is routed to these jacks and can power an external electrical accessory if desired. 

Water tank, tower and feed-water pump

The water tower provides feed-water to maintain boiler level during operation and holds about 3 quarts. Jensen themselves used an upturned Model 50 size brass boiler for their water tank, but those are not exactly to be found laying about. Fortunately a stainless steel cookie "jar" fit the bill nicely and holds a little more water than the real thing...sort of desirable as this power plant gulps water !  

To the right is a closeup of my "replica" logo applied to the tank.

The water tank (cookie jar) has just one hole bored in it's base for the feed-water down-tube, and it is otherwise attached to an aluminum plate with contact cement, as I didn't want to add more holes and potential leak points than needed.  The tank plate is screwed to the tower frame which was built from aluminum "L" angle pieces.

Screwing the tower together was a bit like juggling Jello, but once assembled it took on amazing strength in all those angles.

I learned several years AFTER I built my replica, that I made my tank and tower somewhat larger than an original, having swagged the measurements from photos only.  But,  I love how they turned out none the less and wouldn't change them if I could.

As was used on the prototype and the earlier Jensen 51's, I added an analog "Inches of Water" gauge directly behind the console and tied into the water tower.  It can be seen to the left under the tower and behind the console. 

The Inches of Water gauge lets you see in an instant what the water level of the tower tank is.  I really like having one more gadget to keep an eye on!!

Although the tank/water tower is 30 inches tall, gravity alone will not overcome boiler pressure to supply the needed water for boiler replenishment while running. 

Water is moved into the boiler against  pressure, by the engine driven feed water pump pictured to the right. 

This eccentric driven pump was quite puzzling to me at first.  I struggled to understand HOW it worked and then to get it working properly.

With help from several Jensen 50 and 51 owners, we figured out it's eccentricities and now it works perfectly. 

A combination of keeping the check valve balls clean, using the proper Teflon packing around the piston, using enough spring tension on the pump's water outlet check valve ball and keeping boiler operating pressure about 25 PSI, made all the difference in the world.

Click here for "how to's" on getting the feedpump working as intended.

In the photo to the left you can see most of the plumbing that supplies the feed-water pump from the tower tank. 

The black oval handle is the water shutoff valve at the base of the tower down-tube. 

The more pointed, black handled valve is meant for totally draining the tower tank if needed for moving or maintenance. 

This sort of valve was not used on the original 51's, but it's very handy for complete draining of the water tank with a bit more elegance than a suction tube.  It makes draining the tank a simple, fast, no drip exercise. 

When all is said and done, this replica will heat water to a boil faster and maintain pressure under load more easily than a factory Jensen 51, primarily because of the higher wattage heaters used.  I bring things to a boil with about 13 amps on the incoming amp meter, then dial that back to 9.0 amps to maintain an optimum boiler pressure of 25 PSI, which will handle any load I place on it.

With greater AC and DC generating ability, I was also able to add 5X the lighting and a larger DC motor. The power consumption and drop in engine RPM's is obvious with increased "load", but that's the beauty of this piece.  With switches and gauges galore, you can see first hand how changes in electrical load on a "power station" really effect things.

I can better understand what is happening when an electrical "brown out" occurs during periods of high energy consumption in our homes.  I also understand why many of the customers who bought Jensen 51's over the years were power utility companies and physics depts. of major universities, it's that great a teaching aid. 

It's a lot of fun to work the switches, monitor gauges and tweak the other controls.  I have no regrets having spent the time and funds to create this is the most enjoyable piece of steam hardware I have and one I can start up and let run in the background for hours, topping the water tower off from time to time and checking the gauges, water level, dab of oil etc....all stuff we model steamers love to do.

Click here for factory vs. replica Jensen 51 Comparison Specs and Parts Sourcing

Filmed as of March 2009 showing most of the features incorporated in this replica...I need to update it again as more enhancements were added since filming.

CLICK HERE for an instant video

Another replica 51?

In the June 2009 photo below, I have my 51R001 sitting next to it's almost identical replica just completed for a friend.  I made his tower and tank to the correct measurements since shared by a Jensen 51 owner. 

You can see my tank is a bit chunkier and the tower a bit taller than "spec"...such is life...makes it one of a kind!

In a separate tab on this website, you can follow the build of this second and last replica, 51R002, in even more detail than I captured for my own.


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