In my previous post about Modeling SP Road Switchers (Part 2) - Medium Steam, I briefly touched on the issues with these models.
 |
| SP 3302 Mk-2, with slanted cylinders. About 1946 photo, silver smoke box, with "Lines" on tender - Eddie Sims Collection |
 |
| Ex-Arizona Eastern 903, renumbered as Second SP 3239 in 1924. Post-June 1946 photo - Eddie Sims Collection |
According to Brown Book of HO scale brass locomotives in 1983 Sunset Models imported 290 Mk-2 and and in 1984 an equal numbers Mk-4. There seems to have been a mix-up at the factory in which the valve gear and cylinders were swapped between the two runs of Mk-2/4. The two models that I received from a customer to work on had the outside valve gear on the boiler and frame of the Mk-2 and the inside cylinder (correct for some Mk-2s, but not Mk-4s) on the model with the boiler and frame details consistent for the Mk-4.
Sunset SP Mk-2 Model "Long"
 |
| Box Label from Sunset Model;s SP Mk-2 2-8-2 |
 |
| Left side of Sunset Mk-2, corrected for SP 3207. |
From what I can gather the Mk-2s were the only class fitted with the inside valve cylinders, following the Stephenson design, but with very weird "crossover" valve gear to outside eccentric motion at the main driver. The way the two models I show here were sent to me, the Mk-4 (AE version) had the inside valve cylinders which is NOT correct for any photos I've seen at all. I will quickly add here that some of the Mk-2s with inside valves cylinders were rebuilt with outside valved cylinders like the Mk-4s always had. All of the Mk-2s and Pacific Lines (SP built) Mk-4s seem to have the large sand domes.
 |
| Right side of Sunset Mk-2, corrected for SP 3207. |
Notice that the Mk-2 framed engines with the large sand dome and "sport cabs" are about 12" scale inches longer than the (AE) Mk-4 model below. The prototype photos below seem to bear this out, that there were two different length engines, the "longer" of which were the engines built for originally for the SP as Mk-2 and Mk-4. I'll discuss the "Short" engines below.
Sunset SP Mk-4 Model "Short"
 |
| Box cover for Sunset Mk-4 2-8-2 |
 |
| SP 3224, Mk-4 with right side air pump. - Eddie Sims Collection |
Notice that the SP 3224 above has the large sand dome, airpumps on both sides, and a "sport cab". The engines built for the SP as Mk-2 and -4 seem to have longer lines as well compared to the model below.
 |
| Sunset Models SP Mk-4 after valve gear swap - corrected for SP 3237 (2nd), ex-AE 901. |
 |
| Sunset Models SP Mk-4 after valve gear swap - corrected for SP 3237 (2nd), ex-AE 901. |
Given that the "Short" framed model's details line up better to the ex-AE 901-905 engines (SP 3236-3240), I would say that the Sunset Models engine with the small sand dome, two air pumps on the left side, and square cab is really a model of the Arizona Eastern built engines.
Swapping Valve Gear & Cylinders
To fix the issue of the "Mk-4" having the wrong domes and wrong inside valve cylinders, I decided to swap the frames of the two engines. This revealed another issue. The "Mk-4" with the small sand domes is about 12" scale inches shorter than the other engine! Swapping the frames is out. I then decided to look again at my books and photos, coming to the conclusion that with the parts I could swap the valve gear between the two models was actually fairly simple. Here's the basic steps to do this swap:
 |
| Remove in Inner Smokebox screw. |
 |
| Remove Rear Cab Screws |
Next, remove the two screws in the rear wall of the lower cab, this will release the boiler and cab from the frame.
 |
| The Left Eccentric Screw is VERY small, but shouldn't be too hard to loosen, do not remove it! |
After the boiler is set asside, use a very fine screw driver to loosen the eccentric screws. Do NOT Remove these screws, they only have to be loose enough to slide off the main crank pin.
 |
| Do the same with the Right Eccentric Screw. |
Make sure to remove and keep any washes that are between the side rods and main rods safe. You will need to place them back between the same rods again. Making notes of this is a good idea!
 |
| Remove the Yoke Screws. |
Almost there, next, remove the two yoke screws, this will release the valve gear. Last is the main cylinder blocks.
 |
| Lastly, remove the "outer" screw from the bottom of the cylinder block. |
Lastly remove the main cylinder block screw. This is the "outer" one, which has a hole through it for the inner screw which we removed first that holds the smoke box and boiler on.
Follow these steps on the other engine, trade parts and reinstall.
 |
| Sunset Mk-2 with inside valve cylinders. |
 |
| Sunset Mk-4 with outside valve cylinders. |
It's possible that the previous owner before my customer bought these two Sunset engines did exactly what I undid in trading the valve gear and cylinders to make a Mk-4 with the "SP-style" boiler and "sport cab"... - however I have heard from other people that the cylinders were swapped from some of the engines when new as well. Hopefully these photos of the prototype engines and book photo references will help you in sorting out which engine you want to model!
Mk-2 Photos & Ref's
Several Mk-2s were rebuilt with the later Mk-4 style outside valved cylinders. In these photos both engines have "Sport Cabs" with the slanted front wall to clear access for the staybolts on the rear sides of the firebox.
I'm going to put together a short list of Mk-2 class engines that had the outside valve gear cylinder.
SP 3201 - Photo Feb'52 Lone Pine, SP San Joaquin Valley - Tom Dill, pg.102. 120-SC-type tender
SP 3202 - Inside Valved Cylinders, "Sport Cab", FWH, 120-C-1 Tender. - Eddie Sims Collection (Below)
 |
| SP 3202, Mk-2 - Inside Valvegear, FWH, "Sport Cab", 120-C-1 Tender, 1946 - Eddie Sims Collection. |
SP 3203 - Outside Valve Cylinders, "Sport Cab", 120-SC-tender. - Eddie Sims Collection (Below)
 |
| Mk-2 SP 3203 right side, with outside valve cylinder as Sunset Mk-2 was imported. Owenyo, CA, Eddie Sims Collection |
 |
| Mk-2 SP 3202 left side, clamshell stack, and footboard pilot. Owenyo, CA, Feb 10, 1951, Andrew Brandon Collection. |
SP 3207 - Photo Livermore, SP San Joaquin Valley - Tom Dill, pg.18. - Narrow Cylinders
SP 3208 - I believe I have a picture of this engine in the Southern Pacific Steam series on Mk-class engines by Jeff Ainsworth. - which I've misplaced just as I'm writing this. I will correct this reference when I locate the book again! - The corrected Sunset Model with 120-C-1/2 tender is correct for the photo of 3208 in this reference.
 |
| Mk-2 SP 3208 with Mk-4 type Cylinder as Sunset Mk-2 was imported. Eddie Sims Collection |
 |
| SP 3211, date unknown, but after June 1946. Eddie Sims Collection. |
Mk-4 Photos & Ref's
Note that the SP built Mk-4s have the large sand domes. The Ex-Arizona Eastern Mk-4's 3236-3240, had small sand domes and
SP 3216 - Photo Aug-1955 Livermore, SP Golden Empire 1954-1958, published by SPHTS, 2011. Pg.31 120-C-7 tender.
SP 3216 - Photo July '53 Livermore, SP' San Joaquin Valley Line- Tom Dill, pg.18.
 |
| SP 3216, with 120-SC tender and large forward mounted sand dome. Engine out of service. - Eddie Sims Collection |
SP 3218 - Photo June'54 Tracy, SP' San Joaquin Valley Line - Tom Dill, pg.25. 120-SC-type
 |
| SP 3218, Mk-4, with 120-SC-tender, FWH, and large forward mounted sand dome. - Eddie Sims Collection. |
SP 3227 - Photo July-1956 W.Oakland, SP Golden Empire, pg.17 120-C-3/6 tender
SP 3227 - Photo Jan-1953 Little Lake, SP's San Joaquin Valley Line - Tom Dill, pg.101. 120-C-3/6 tender
 |
| Right side of SP 3227, Mk-4 with 120-SC-tender with raised bunker, large forward sand dome. - Eddie Sims Collection. |
 |
| Left side of SP 3227, Mk-4 with square cab and no FWH. - Eddie Sims Collection |
 |
| SP 3235, Mk-4, "Sport Cab", 120-C-2 tender, large forward mounted Sand Dome. - Eddie Sims Collection. |
SP 3236 - Photo July-1956 W.Oakland, SP Golden Empire, Pg.18 120-SC-type tender - no headlight
SP 3237 (2nd) Ex-AE 901 - Photo Lone Pine, SP's San Joaquin Valley Line - Tom Dill, pg.101. 120-C-3/6 I believe there is an additional photo of this engine in the Southern Pacific Steam series on Mk-class engines by Jeff Ainsworth. - which I've misplaced just as I'm writing this. I will correct this reference when I locate the book again! - The corrected Sunset Model with 120-C-1/2 tender is correct for the photo of 3237 in this reference as well as the picture in Tom Dill's SP'San Joaquin Valley Line.
 |
| SP 3239, Mk-4, Ex-AE 903, small sand dome, sqr. cab, FWH. Also note how short the engine looks. - Eddie Sims Collection. |
In Closing
From these two photos (SP 3239 above, and Sunset Mk-4 below), it is pretty clear that the Sunset Mk-4 model's boiler was designed to replicate the Ex-Arizona Eastern's 901-905, which were renumbered as SP's Second 3237-3240 in 1924.
 |
| To Make the SP 3239 from a Sunset Mk-4, the rear left air pump would need to be replaced with a Worthington FWH. |
At least now my customer's two models both have a correct prototype to be finished as and be accurate for. I really like these small-drivered 2-8-2s, they have really grown on me over the last few years seeing them in more pictures working locals in the areas I'm interested in modeling.
I'm sure I'll be doing more blogs on these two models as they are painted and finished. This post was mostly to put out some information about the differences between the Sunset Models Mk-2 and Mk-4 models and some photos to show what the real engines looked like at various times in their careers. A big THANKS! to Eddie Sims for the use of the photos in his collection.
Edit: Several followers of the blog have responded to this post and shown their "Mk-4" models that came with outside valved cylinders but the small dome, which they replaced with an after-market dome. I've also seen one model that came as my customer's did with the Mk-2 "long frame" engine with sport cab and large dome, but fitted with the outside valve cylinders. So it would seem that there is quite some variation in what Sunset brought in with the two runs of Mk-2 and two runs of Mk-4.
Jason Hill
Related Links:
Modeling SP Road Switchers (Part 1) - Small Steam
Modeling SP Road Switchers (Part 2) - Medium Steam
SP Tender Swapping (Part 1) - A Game for Prototype Modelers
New Drawbar Mount for Athearn-Genesis 120-C-6 Tender
Enjoy the other Night Owl Modeler blog posts as well.
Thanks for doing this Jason. I recently picked up a MK-4.
ReplyDelete