IndianaRog and the Temple of Steam

Miniature steam engines by Jensen, Karsten, Stuart & Empire. Lionel & MTH trains. Wind up clocks & watches plus black powder cannons and mortars.


Jensen Chronology & Varieties

I have been most fortunate to have two leading Jensen collectors (Bill Wheeler and Gil Garceau) offer to let me provide a "home" for their historical work on Jensen engines, here in the Temple of Steam. 

My only contribution has been to format and host the information to fit within this website.  The steam community owes Messrs. Wheeler and Garceau a big thank you for researching and making this information available. 

Is this the last word?  NO...both Bill and Gil have stated there are many exceptions to the "rules" and new information continues to surface regularly.  I
n their words the mystery of the history will continue to unravel!  If they provide further updates, I will include them here. 

The information is organized as follows as of August 2010:

1) Jensen Chronology

2) Jensen No. 10 Varieties

3) Jensen No. 20 Varieties

4) Jensen No. 25 Varieties

5) Jensen No. 50 & 51 Varieties

Jensen Chronology.

Model      Years in Production
======   =================
No. 10
  -  1932 to 1960's (to date if you allow for the 25G)


No. 20  -  1932 to present (possibly called No. 10 if with genset or "Big Power Plant")

No. 15  -  1935 to present

No. 35  -  1935 to 1959

No. 5    -  1932 to 1960's

No. 25  -  1932 to present - wood or stamped base ?

No. 55  -  1947 to present

No. 100 - 1947 to 1985

No. 50  -  late 1930's to 1996 (official retired 10/29/10)

No. 45  - 1949 to 1959

No. 75 Version 1 -  alcohol burner early 1950's to 1960

No. 70  -  1959 to present - wood or stamped base

No. 75 Version 2 -  1959 or 1960 to present (stamped base)

No. 80  -  we believe 1980's

No. 30  -  1960 to 1985 (vertical boiler with No. 25 engine) - wood or stamped

No. 40  -  1960 to 1965 (No. 30 with No. 5 engine)

No. 90  -  1961 (approx. 25 sales samples produced) - 1988 (25 more made)

No. 60/76 -  1960's to present

No. 65  -  1960's to present

No. 85  -  1970's to present

No. 51  -  1973 to 1996 (officially retired 10/29/10)

No. 95G -  2006 to present
=============================================

Specific Jensen features & timeframes:
  • Reversing gear introduced? #20 (1956), #55 (1947/48), then #10 & #25
  • Boiler escutcheon pins (rivets) used? 1932-'40 & 1945-'46, none to date
  • Firebox styles used? 1932-'60 smooth black, embossed brick to date
  • Wood base styles used? 1932-'50 solid wood, 1951-'79 plywood, 2003 to date 25G on plywood
  • Handle material/style used?  1932-'34 packing gland/"horn", 1935-'49 black straight wood, 1949-'70 red straight wood, 1970-'02 red contoured wood (small), red contoured wood (large) to date
  • Cord type used?  1932-'48 cloth, rubber to date
  • Plug type used?  1932-'40's bakelite, rubber to date, 2 prong 1932-'73, 3 prong to date
  • ID Plates?  1932-'46 decal, 1947-'51 brass, aluminum to date
  • UL Decal?  1949/'50-'54

Jensen No. 10 Varieties.

Version 1. Four Screw #25 engine with horseshoe magnet genset on same shaft.

V.1a
(1932-1935  -  Robin's egg blue, coil heater, white handles)
V.1b (1935-1938/39 - Robin's egg blue, core heater, black handles, solid wood base,decal, boiler with escutcheon pins(rivets))
ONE V.1b found with "bone" handles - possible variation
Did all have separate light posts mounted on wood base?  Yes

Version 2#25 engine with horseshoe magnet genset on same shaft.

V.2a
(1938-1939 - Robin's egg blue, rivets, decal, cloth cord, bakelite plug)
V.2b (1945-1946 - Dark blue, rivets, decal, cloth cord, bakelite plug)  Used up remaining boilers with rivets, separate lamp post immediately post war.
V.2c (1946-1947 - Dark blue, NO rivets, cloth cord, bakelite plug)
V.2d (1948-49/50 - Red magnet, brass ID plate, cloth/rubber cord, rubber plug, no UL)
V.2e (1949/50 - Red magnet, brass ID plate, rubber cord & plug, with UL label) solid wood base, plywood base from mid '49, possible variation.
Did all have light posts mounted on the gensets?  NO, but they were after the riveted boilers were used up.

Version 3.  #25 engine with red Omega magnet genset on same shaft (1951 only).

Version 4.  #25 cast iron engine with genset on separate base driven by spring belt.

V.4a
  (1952-1954  - with UL Label)
V.4b  (1955-1959  - no UL Label)
V.4c  (1960-1961 forward - brick firebox)

Version 5.
  #25 stamped base engine, brick firebox.

V.5a
  (1961-1979  - cast iron genset)
V.5b  (2003-plus  - stamped genset {called #25G})

Jensen No. 20 Varieties.

Version 1. #20 engine w/horseshoe magnet genset on same shaft                 

V.1a (1932-'33(?))  -  Robin's egg blue, packing gland handles
V.1b (1935-'38/39) - Robin's egg blue, black wood handles
V.1c (1945/'46) - Dark blue, black wood handles (solid wood base, decal, 3" boiler with escutcheon pins (rivets), separate light)

Version 2.  #20 engine w/ separate horseshoe magnet genset

V.2a (1946-'48(?)) - Dark blue, black handles, cloth cord, no rivets
V.2b (1948(?)-'50) - Red magnet, black/red handles, rubber cord (solid wood base, brass ID plate, no rivets, some parts crossover during transitions)


Version 3.  #20 engine w/ separate Omega magnet genset (1951 only).

Version 4. #20 engine w/ reverse

V.4a  (1956-'60)  - Dark blue, separate 3 piece magnet genset
V.4b  (1961(?)-'65)  - transition to new style firebox & boiler boiler, Round window boiler 1965 to date 

Version 5.  #20 engine w/ new style boiler & firebox                              

V.5a  (19??-'80's)  - green, some w/o generator (20R)
V.5b  (1980's - date) - blue-green, some w/o generator (20R)

 

NEW INFO:

All #20 sized engines that had a generator from the factory were known as a Big Power Plant or #20 Big Power Plant before 1992. The style numbers were first assigned post war in the 1940's.  It would not be until 1992 that Jensen added the 'G' designation (for generator). From that time forward, the Big Power Plant became known as the #20-G.

The cylinder assembly overall length is about 1/4 inch shorter on #20 engines from 1932 thru the early 1960's.  Not sure what year they got longer (yet), but it is very clear that a newer #20 cylinder will not work on an earlier cast engine base.  The mounting posts on the earlier style castings are 1/4 inch closer to the main bearing support post.

Jensen No. 25 Varieties.

Version 1. 1932 - ?  Solid wood base, escutcheon pins (rivets), Robin's egg blue, no reverse gear, four screw cylinder, cloth cord & bakelite plug (some have packing gland or "horn" handles)

V.1a  Ceramic, round hot plate type heater
V.1b  Chromalox heater
V.1c  Cartridge heater

Version 2.  1937 - '38/'39 - small cylinder, solid wood base, rivets, Robins egg blue, no reverse gear, cloth cord & bakelite plug

V.2a  Blanket heater
V.2b  (1945-'46) - Solid wood base, rivets, dark blue, no reverse gear, cloth cord & bakelite plug

V.2c  (1946/'47) - Solid wood base, rivets, dark blue, no reverse gear, cloth cord & 2 prong rubber plug

Version 3.  1946/'47- '48 - Solid wood base, no rivets, dark blue, no reverse gear, cloth cord & 2 prong rubber plug

Version 4. 
1949/'50's - Plywood base, no rivets, dark blue, no reverse gear, rubber cord & 2 prong rubber plug

Version 5.  1956-'60 - Plywood base, no rivets, dark blue, with reverse gear, rubber cord & 2 prong rubber plug

Version 6.  1960/'61 - Transition to new style boiler and firebox.  Some have new style boiler & embossed brick firebox.  Some have embossed brick firebox but old style boiler.  All still have blue cast iron engines with reverse gear, plywood bases & rubber cord and 2 prong rubber plug.

Version 7.  1961-'73 - New style boiler & embossed brick firebox, metal bases, 2 prong rubber plug and cord

Version 8.  1973 to date - New style boiler & embossed brick firebox, metal bases, 3 prong grounded rubber plug and cord

Jensen Model 50 and 51 Varieties.

Type 1A v1:   Most likely the 1938-1940 era. 

- The earliest Jensen #50 known is in possession of a steam group, on loan from a present or past member.  It is felt to be the prototype or the earliest production version. 

- Solid wood base, milled like the Jensen bases of the thirties and forties

- Riveted boiler of 6 inches diameter and long angled sight glass standing fairly far off the face of the boiler

- The pressure gauge has a c. 75 degree arc and the whistle handle is black

- The generator has the early large, thin base and a separate light standard

- Generator and engine cast bases are light (robin's egg) blue

- Two ceramic insert heaters were used and the receptacle base only accommodates two larger round plugs

- Cords are cloth covered

- NO decal or ID tag was used

- The most unique feature is the throttle housing which seems to be an oversized standard Jensen type from their other engines of the late 1930's, not the later #50 type with the round valve wheel  

- So far there is only one known example of this very early version


Type 1A v2:  Most likely the 1938-1940 era.

- Most notably has the same 6 " diameter boiler as Type 1A v1

- Standard (to the #50) round valve wheel in a squared housing where the steam line exits straight down

- The generator has the early large, thin base and a separate light standard

- Generator and engine cast bases are light (robin's egg) blue

- Two ceramic insert heaters were used and the receptacle base only accommodates two larger round plugs

- Cords are cloth covered

- Has the Jensen decal

- So far there is only one known example of this very early version


Type 1B:   Most likely the 1938-1940 era. 

- Similar to 1A, but with the standard (to the #50) round valve wheel in a squared housing where the steam line exits straight down.

- Also had 5 inch diameter riveted boiler.  All #50's from this point forward have the 5 inch diameter boilers

- The generator has the early large, thin base and a separate light standard

- Generator and engine cast bases are light (robin's egg) blue

- Two ceramic insert heaters were used and the receptacle base only accommodates two larger round plugs

- Cords are cloth covered

- Has the Jensen decal



Type 2A v1:  Most likely the 1946-1947 era. 

- Breadboard style base (solid wood with end caps)

- The boiler is still riveted, but the sight glass is mounted much closer to the face of the boiler

- The pressure gauge has a c. 180 degree arc and the whistle handle is red

- The generator is the standard blue with a blue horseshoe magnet.  

- Generator and engine cast bases are the brighter dark blue

- Two ceramic insert heaters were used and the receptacle base only accommodates two larger round plugs

- Cords are cloth covered

- Early Jensen decal was used.


Type 2A v2:  Most likely the 1948-1950 era.

- Breadboard style base (solid wood with end caps)

- The boiler is still riveted, but the sight glass is mounted much closer to the face of the boiler

- The pressure gauge has a c.180 degree arc and the whistle handle is red

- The generator base is the standard blue but with a RED horseshoe magnet

- Generator and engine cast bases are the brighter dark blue

- Two ceramic insert heaters were used and the receptacle base only accomodates two larger round plugs

- Cords are cloth covered

- Early Jensen decal was used.


Type 2B:  Most likely the 1949-1950 era. 

- Similar to 2A, but with the red horseshoe generator magnet.


Type 2C:   Most likely 1951

- Given the unique round, Omega style generator magnet machined from a single piece of magnetic iron and offered in 1951 only. Otherwise similar to 2A and 2B except the cords may be cloth or rubber or mixed.  An example was sold in the 1995 Owl's Head auction and had a $1,500 hammer price.


Type 2D:  Most likely the 1952-1954 era. 

- Similar to 2C, except it utilizes the three piece magnet generator style introduced in 1952 to replace the Omega style generator.

- During the remainder of the 1950's, the base was modified to be made from a double layer of plywood and the rivets were deleted from the boiler.  The exact dates of these changes are unknown.



Type 3:  Most likely the 1960-1961 era, based on an original owner's recollection 

- Plywood base used as with all subsequent manufacture  

- The boiler is not riveted, but the sight glass is still the long angled closer mounted type

- The pressure gauge has a c. 180 degree arc and the whistle handle is red  

- The generator is a three piece type.  Generator and engine cast bases are the later darker dark blue  

- Two ceramic insert heaters were used and the receptacle base only accommodates two larger round plugs

- Cords are all rubber covered as with all subsequent manufacture

- There are numerous small variations in the way parts and appliances were made during this period as would be normal as Tom, Sr. brought these into production

- #50's built by Tom, Sr. during this period lagged behind the other Jensens produced at that time in terms of builders plates and some other details

- #20 brass ID plate was used, with the "20" removed and "50' stamped over it as was done with the early #55's (the watts and amps remain unaltered, although not appropriate)



Type 4: Most likely the 1961 - 1965/6 era. 

- Boiler is not riveted and has the three round sight glass configuration as with all subsequent mfg.

- Boiler ends are still flat and the through-bolt is still present  

- The heater arrangement is the same as the previous group with the addition of a third, saddle type heater with the appropriate changes to the receptacle and the necessity of changing to the flat brown plugs still seen on a #50 delivered in 2006

- The firebox and stack base are changed to the embossed copper colored type  

- Generator and engine cast bases are green

- The cylinder lubrication cup is added

- The small aluminum ID plate is stamped with the appropriate style and amp information (assumed to be the first #50's to have correct tag data)

One exception to this type:  The prototype for the 3 heater design was a test bed engine that spent a good 6 months on Tom Sr's. desk as he worked with it.  This engine has what was likely the last remaining left over riveted boiler and 3 heaters and the embossed copper colored firebox.  It still had just 2 heater plugs as one of them was wired to a cartridge heater as well as a blanket heater via the chimney stand.  The remaining plug fed just one cartridge heater.  There is only one like this.



Type 5:  Most likely the 1966 - 1976 era.

- Same as type 4 but with three immersion heaters. It is assumed that Tom, Sr. decided he needed more heating power (or maybe wasn't able to obtain heaters of high enough wattage), so he added the saddle heater as in type 4, using up the existing stock of boilers, then changed to this heater arrangement

- Some of these were painted green and some seem to be metallic green  

- The flange was first added to the feedwater pump and later (maybe in the next variation) to the valve rod chest

- Some of these (possibly the later ones) had small cup like water towers mounted between the firebox and the feedwater pump

- In addition to a larger aluminum ID plate, some of these had a plate with a facsimile of Tom, Sr's. signature as well as a date of manufacture and a serial number. 

- A known #50 example dated 12-15-76 bears #385 serial number (which may have been either the 85th or 185th #50 made), has the small water tower and metallic green paint.  



Type 6: Most likely the 1977-1996 era. 

- It is believed that when Randy Calhoun joined the Jensen team c. mid 1970's, Tom, Sr. was involved with updating yet again the #50, while Randy Calhoun developed and built the #51 prototype in 1977. Tom Sr. decided along with Randy that they would like to make it a high end production steam power plant.  Tom Sr. would build a #50 engine and get it delivered to Randy who then went about acquiring the needed parts and assembled the #51.  Each of these was a hand built masterpiece start to finish.

- At some point between 1977 and 1981, Tom, Sr. changed the front boiler end to the present convex type and eliminated the through-bolt  

- At some time during the Type (5) and Type (6) period, the pressure gauge type became a c. 270 degree arc

- A known #51 example dated 3-15-83 bears serial number #51-411 and it is believed to be the 11th #51 made

- Another known #51 example is dated from 1996 



Type 7:  Since Tom, Sr. passed away in 1992, it is believed that few additional #50's or #51's were made beyond one known 1996.  A #51 was ordered in late 2001 or early 2002 from Tom, Jr., who agreed at the time of the order to make the water tower, but not a complete #51, hence this one sans control panel was dubbed by it's owner to be a #50 1/2, and was delivered in June 2006.  It has a convex rear boiler end as well as the convex front boiler end and is assumed to be Tom, Jr.'s most recent #50.  The owner notes it is an enjoyable runner had logged over 800 hours on it by the end of 2006.

Epilogue:  Jensen officially retired the Jensen 50 and 51 models on Oct. 29, 2010 noting cost of materials and difficulty of manufacture prohibited resurrection.



In Summary: Somewhere between 250 and 300 model #50's were made by Jensen, including those used in the further manufacture of model #51's.  It is estimated that 27 of the #51's were assembled by Jensen and Randy Calhoun and that 1 or 2 were assembled and wired by John Loughner.