Questions that keep getting asked. This is your resource for the answers.

Updated 2/7/2021
  • Building the T1 5550 Reasons

  • Why choose the T1 Duplex

    There are a number of reasons why we chose the T1 for our project. First and foremost, we’re PRR fans in general, and T1 fans in particular. Personal preferences aside, there are a number of other reasons why we feel it should be recreated: – The PRR didn’t preserve one in the historic collection at Northumberland. – Of the PRR duplexii, it was the most widely produced (52 units), and if we want to build a late PRR design, it would be the most representative. – Of all the Duplexes, it was the only class capable of running anywhere in system (The S1 was limited to between Crestline and Chicago, and the Q2 could only move light as far east as Altoona) – It possessed a combination of features that wasn’t utilized anywhere else (Franklin Poppet valves, Duplex drive, and Loewy styling), and was therefore unique. The uniqueness of the design is the main reason we’d like to see it reproduced. There are a lot of other large steam locomotive restoration projects ongoing, and we need to do something to set ourselves apart from other organizations making appeals for donations. If completed, the T1 would be the only poppet valve locomotive operating in the USA, and the only rigid frame duplex anywhere in the world. Finally, there is so much conjecture on the T1’s actual performance – whether it could actually attain the speeds attributed to it, or how difficult they were to operate and maintain – that it would put to rest a lot of questions regarding what the design was capable of. There is more potential for learning in the process of rebuilding a T1 than there would be a more “conventional” design, and we’d have the opportunity to validate the revolutionary ideas of the men who created it.

  • Why not build something proven like a A, J , Berkshire, or a modern Hudson shrouded like the 20th century limited?

    As was alluded to in another question – there’s very little to be learned from building a “proven” design. Moreover, most of the other classes suggested either still exist, or are similar enough to other extant locomotives that their configuration is already represented in the heritage fleet. There’s no point in building another Berk or 4-8-4 when there are so many running or restorable examples already out there. There are 4-6-4 and 2-10-4 projects ongoing that we don’t want to be in direct competition with for resources or public attention.

  • The money spent on building a T1 would go a long way toward restoring the PRR engines in Strasburg. Why don’t you restore one of the other existing PRR locomotive classes to operation, or build a replica of one of them?

    Numerous reasons – foremost is that we don’t own any of the existing locomotives, nor are we likely to encounter one that is available for sale. The bulk of the PRR historic collection, now in the possession of the Railroad Museum of Pennsylvania, is owned by the State of Pennsylvania. The PA Historic Museum Commission regards these locomotives as artifacts, and presently will not allow the sort of “alterations to the historic fabric” necessary to restore them to operation. Unless this policy changes, that leaves the two Long Island G5’s (#35 and #39), The I1 in the possession of the WNYRHS (#4483), and the K4 owned by the Railroader’s Memorial Museum in Altoona (#1361) as the only potential restoration candidates. The 39, 1361, and 4483 are already being restored, or considered for restoration by their respective owners, so we wouldn’t want to duplicate their efforts, or compete directly with a similar design. That leaves the D16, E6, H10, L1, or M1 as candidates for duplication, or one of the extinct F3 or N1 classes for replication. The D, F or H would make a great candidate for a short line, but not so much for mainline service. Besides, there are plenty of 4-4-0’s, 2-6-0’s and 2-8-0’s already running, so if there were interest in replicating one of those for short line service, The Strasburg Railroad or another locomotive builder would already have done so. An L, M, or N would be great to see run – but they’re an awkward size that’s too heavy for most short lines, but not fast enough for mainline service, except possibly the M1. We’d probably have a harder time answering the “where will it run” question with one of those than a T1. We could replicate the E6, which certainly is small enough to operate on a short line, and fast enough for mainline service – but by the time we built the three (or four) of them needed to pull today’s excursion trains, it might be less costly to just build the T1.

  • General Trust Background

  • How Much Will It Cost?

    The short answer is 10 million dollars. How did we get there? That’s the fun part, but only if you like math. There are several ways to approach the question. The most obvious way to estimate cost might be to consider inflation. The average cost of a T1 in 1945 was about $320,000. Using data from the Federal Reserve, and its Consumer Price Index (CPI), the cost of a new T1 in 2013 is an estimated $4,175,324.68. Unfortunately, that number does not take into account lost skills, knowledge, and tooling that will have to be relearned, rebuilt, or replaced with modern alternatives as the T1 project progresses. In the worst case scenario, the cost could be seven times as high. Consider for a moment the following example. An original A1 built in Darlington cost £16,000 in 1948. The inflation in Britain over the time period 1948 to 2008 was 2,623%. At that rate, one would expect the final cost of Tornado to be £419,680. It was in fact more, seven times more. The final price tag for Tornado was in excess of £3 million. Why is that? In many instances batch production tends to spread cost, whereas the production of a single unit tends to add cost. There is however a silver lining. In the case of Tornado cost savings of up to 33% of the original cost were achieved during some stages of construction. For example, fabricating a disposable mold used for one part is less expensive than manufacturing a mold which will be used repeatedly to produce 50 parts. In order to reduce expense, the 5550’s construction will employ modern techniques such as CNC, and rapid prototyping when, and where-ever possible. Smaller castings with specialized joints for welding may help to further reduce costs, especially in the case of the T1’s large frame. Another method of calculating cost, is to do so by weight. Tornado weighs 167 tons and cost 5 million dollars. That’s a cost of $30,000 per ton for Tornado, and we’ll use that to calculate the T1’s cost based on its weight. Depending on who you read, production model T1 weight is reported from 318 to 346 tons. The average is 332 tons, almost exactly twice the weight of Tornado. So that should be just about twice the cost, or $9,960,000. Let’s call it 10 million. Next, we consider total heating surface, and firegrate area. Total heating surface for Tornado is 2,461 sqft, and at a total cost of 5 million dollars, that’s $2,031 per sqft. Total heating surface for the T1 is 5,639 sqft, at $2031 per sqft, that’s $11,452,809. Turning to firegrate area, Tornado has a grate area of 50 sqft, and that’s pricey real estate at $100,000 per square foot. Grate area for a T1 is 92 sqft, so 9.2 million dollars. Finally, we look at length. Tornado measures 73′ buffer to buffer. That’s $68,500 per foot. The T1’s wheelbase is 107′ which gives us $7,329,500. That helps take the edge off the earlier 11.45 million dollar figure. In the end, it’s going to come in really close to 10 million dollars.

  • Alternative Fuel Options

    The locomotive will be used as a test bed for alternative environmentally friendly fuels to allow operation of America’s steam locomotives into the foreseeable future. The locomotive would be a national touring education center when complete while testing coal alternative fuel sources such as torrefied biomass, natural gas, vegetable oil, recycled oils and propane. As well as fuel sources being tested, combustion and drafting would also be tested for increased combustion performance and reduction in carbon output. Results would be shared with operators around the country as well as plans for coal to other fuel conversions.

  • How Can I help?

    Spread the word The T1 Trust has had volunteers promote the 5550 project at train shows and at museum open house events. Trifold brochures are free for the asking and supporters are encouraged to request and distribute the Trust’s trifold brochures. Perhaps you could put The T1 Trust in touch with your local historical society, we’d be happy to give a lecture about the history of the PRR T1 and about the 5550 Project. Pledge your Support To date The T1 Trust has raised over $1,375,000 in cash and in-kind donations. A variety of exciting opportunities to give are featured in the Fundraising portion of the Trust’s website these opportunities include driving wheel sponsorship, the sponsorship of other parts, blueprint sponsorship, regular monthly giving, one time donations, and membership in The T1 Trust Founders Club. As part of its 2015 Kickstarter campaign the PRR T1 Trust offered bronze keystone number plates cast with the original T1 #5550 pattern made by Chuck Blardone. The keystones were offered as premiums for donations of $5,000. The T1 Trust is pleased to continue this remarkable opportunity for interested supporters to secure their very own piece of railroad history. If you would like more information on how you can support the PRR T1 Trust and receive a full sized bronze 5550 keystone please send an email to or send a letter to the address below. Some donors may be less interested in the month to month fundraising drives and more interested in the project’s success overall. For these donors a life-income gift to The T1 Trust may be the preferred method of contribution. In order to meet this need, the Trust has established the 5550 Keystone Society. This name was chosen to emphasize the pivotal role these gifts have in making 5550 a reality. The 5550 Keystone Society is a group of PRR T1 Trust supporters who have made an enduring pledge to railroad preservation by offering a charitable life income gift to the PRR T1 Trust or by naming the Trust as a beneficiary in their estate plans. The 5550 Keystone Society is a way for us to appreciate and honor these remarkable individuals for the generous contributions they have made to secure the future of the PRR T1 Trust and PRR T1 #5550. Members of the 5550 Keystone Society, receive exclusive benefits and confidential details about the efforts of The T1 Trust. 5550 Keystone Society members receive the Trust’s quarterly newsletter, “The T1 Trail Blazer”, which contains news and special features describing how the Trust is building the magnificent T1. Keystone Society members also receive a personalized certificate of membership suitable for framing, a full size print of the 5550 launch painting, The T1 Trust’s annual report, and invitations to special events. For further details, or to become a member of The 5550 Keystone Society please send an email to the Trust’s Legacy Manager or write us: The PRR T1 Trust PO Box 552 Pottstown, PA 19464 Make a Donation

  • Where will the T1 Trust find someone to make a cast engine bed or frame for this project.

    So far, we’ve identified one foundry that is capable of making a casting that large, and has expressed interest in participating – Bradken Engineered Products in Atchison, Kansas. They have the ability to pour up to 120,000 lb. of steel in a single part, and have experience in casting parts for the railroad industry. Unfortunately, a 60 ton pour will typically yield a part of about half that weight after gates and risers are removed, and we estimate that the T1 frame is somewhere between 37 and 44 tons. Because of the weight and complexity of the T1 engine bed, we may be forced to fabricate the frame from several smaller castings, or from welded plate. The exact details of the revised frame design are still being evaluated.

  • How much of the original drawings, material specs, etc. exist for the T1?

    According to the master drawing lists for the T1, there are 1,530 PRR part numbers associated with the T1 and Tender. Of these, 350 of the original large format drawings are known to exist in the PRR collection at the State Archives in Harrisburg. We do not yet know how many of the original small format drawings still exist, but most of the PRR engineering drawings were microfilmed in 1954. These films are available in both the State Archive in Harrisburg, and the PRRT&HS archives in Lewistown. If a component can’t be found in either of the PRR sources, the BLW archives are also available at Harrisburg, although they have not been fully catalogued, and we don’t know how complete the Baldwin T1 drawing set is. Most of the major structural components are identified as either Nickel Steel, or Timken High Dynamic steel, both of which we have identified the mechanical and chemical properties for. We feel that presently, we will be able to access better than 90% of the original design information. We may have more difficulty in documenting the Timken bearings, Franklin Railway Supply components, or other catalogue items purchased from outside suppliers.

  • Is it going to be “Amtrak Compatible” with ATC and ACSES for the NE corridor plus PTC for mainline operation in the rest of the country?

    Yes. We will outfit the engine as needed to communicate with the host roads on which it will operate. At present, the original PRR cab signals would still work over portions of the NS system. However, as each road uses a different set of hardware, and there is no “standard” system, we have not yet determined how the system for the 5550 will be configured.

  • Will 5550 be fitted with ditch lights, like most modern locomotives?

    At this point – no, there are no plans to equip 5550 with ditch lights. FRA regulations for steam locomotives have no specific requirement for ditch lights: § 230.86 Required illumination. Basic Version a) General provisions. Each steam locomotive used between sunset and sunrise shall be equipped with an operable headlight that provides illumination sufficient for a steam locomotive engineer in the cab to see, in a clear atmosphere, a dark object as large as a man of average size standing at least 800 feet ahead and in front of such headlight. If a steam locomotive is regularly required to run backward for any portion of its trip other than to pick up a detached portion of its train or to make terminal movements, it shall also be equipped on its rear end with an operable headlight that is capable of providing the illumination described in this paragraph (a). b) Dimming device. Such headlights shall be provided with a device whereby the light from same may be diminished in yards and at stations or when meeting trains. c) Where multiple locomotives utilized. When two or more locomotives are used in the same train, the leading locomotive only will be required to display a headlight. But since we’re new construction replicating a historic piece, not an *actual* historic piece, we may be in a grey area. From our initial conversations with the FRA, we got the impression that they don’t differentiate between old and new steam locomotives. However, we’ll need to confirm this with both the FRA and host railroad before the locomotive enters service.

  • Looking at the pictures of the T1 there seems to be massive amounts of weight from the steel. I’m sure to some extent this is figured in the design and balance of the locomotive. With new technology in metallurgy since the original T1’s, will any lighter weight metals be used on this T1 to save weight?

    Generally speaking, the answer to this question is “no” – or at least, not to any significant extent. The principal reason for this is that the T1 needs all of the weight it was originally designed with for rail adhesion. The T1 had a designed factor of adhesion over 4.1, which is generally considered ideal for a steam locomotive. Even though it would be possible to reduce weight by going with higher strength alloys in some applications, taking weight out would reduce the factor of adhesion, resulting in an increased propensity for wheel slip. Given the T1’s reputation, it would not be advisable to reduce factor of adhesion significantly. To counteract a sizeable weight reduction and maintain factor of adhesion, we’d need to significantly reduce the power that the locomotive was capable of, which would severely limit the locomotive’s high speed potential. We do not need to reduce weight to satisfy modern axle loading limits, so there’s little to be gained by a weight reduction program. Another reason not to go for lightweight alloys is stiffness. Even though there is a lot of variation in strength to weight ratio among various alloys, there is almost no difference in stiffness to weight ratio. A thinner, lighter alloy will reduce stiffness, which may result in unforeseen failure modes not present in the original design due to the increased flexion. As it is, we may need to add ballast to counteract weight loss resulting from manufacturing decisions. For example, we intend to build a fully welded boiler instead of the riveted design originally used. Even though we will be maintaining the overall size, thickness, and alloys used originally (to maintain structural stiffness of the boiler), the loss of the overlapping seams of the riveted design will result in weight loss. This will probably be in excess of any weight increase resulting from the thicker firebox needed to maintain the current federally mandated safety factor of 4.0 on boilers. (PRR Belpaire boilers were designed to a lower safety factor acceptable at that time.) Additionally, we also intend to use the Franklin Type B2 rotary cam valve gear, instead of the Type A oscillating cam gear that the T1 originally used. Our decision to use rotary cam valve gear is driven by ease of maintenance and reduced fabrication costs compared to the oscillating cam gear, but the rotary cam gear weighs about three tons less, so we may need to ballast the locomotive to maintain weight distribution. The only area that we may elect to substitute a different material is the poppet valves. The originals were made of a high alloy steel that had some issues with durability. To improve reliability, we may investigate an alternate high strength material such as titanium. This might reduce the valve weight from approximately 4 pounds to as little as 2.5 pounds. Not a significant savings in the big picture (50 pounds total), but lighter valves will reduce reciprocating mass, which will allow for softer return springs. This will reduce the closing force on the valve seats while keeping valve float in check, which should improve reliability beyond any improvements based on alloy strength alone. Despite its age, the T1 used a lot of very high strength and light weight alloys in its construction. The cab, boiler jacket, and streamlining were made of 6000 series aluminum, which saved about 16,000 pounds compared to a steel skin. Siderods, piston rods, crossheads, and crankpins are made from Timken high dynamic steel, which has a yield strength of 110,000 psi, and a high elongation. Spacecraft grade 7000 series aluminum was used for the crosshead shoes. Nearly all the large castings used General Steel Castings’ Nickel Steel. This nickel steel alloy had a much higher elongation than is typical in commercially available steel alloys today. Fortunately with the help of Beaver Valley Alloy and a national materials testing laboratory, The T1 Trust has been able to utilize 21st Century technology to successfully replicate General Steel Castings’ Nickel Steel.

  • Who will build it?

    There are a number of railroad contractors who can fabricate the components necessary to build the locomotive. These include Diversified Rail Services, Steam Operations Corporation, Steam Services of America, and the Strasburg Rail Road. The T1 Trust has already worked with the Strasburg Rail Road on engineering for the T1 and in tapping the threads for the 5550 Keystone. Diversified Rail Services has completed construction of the headlight for 5550 and is currently making the prow hinge. The T1 Trust is looking forward to doing business with a multitude of qualified vendors in realizing the completion of T1 number 5550.

  • What work as been done already?

    The research alone involved in this project is no small task. We’ve read most of the published literature on the T1 to get a feel for the real problems that existed with the design, and develop plans to address them. T1 Trust volunteers have gathered over 1,000 original engineering drawings and test reports for the T1 from the PRR and Baldwin Locomotive Works collections. The archival blueprints have been used to generate 3D CAD models for many of the parts in Solidworks, and we’ve contacted suppliers for tooling and component manufacturing. The massive and complex wooden patterns for the T1’s driving wheels were constructed at Liberty Pattern in Youngstown, Ohio and on February 26, 2016 the first driving wheel was cast at Beaver Valley Alloy in Monaca, Pennsylvania. The T1 Trust’s engineers have developed plans for an all welded boiler, and as the CAD modeling effort continues, more attention will be focused on the design of a revised locomotive frame. Ultimately the design will be subjected to multi physics testing to ensure optimal performance. In addition, The T1 Trust plans to produce a few more “showpiece” parts for public display, to raise awareness and to encourage donations.

  • When will the project be done?

    Our current estimated completion date is 2030. This was based on our own internal estimates of the number of man hours required to complete certain tasks, as well as the duration of the A1 “Tornado” project in the UK. In reality, the program timing will likely be dependent on manpower and funding. If we don’t get the volunteers needed to complete the engineering and construction, or the funds to produce the parts, it could take much longer. Conversely – if we received a donation of $20 Million tomorrow, we could hire a full time professional engineering and fabrication staff, and the project could be completed in as little as 5-6 years.

  • Where will it run? Something like an NKP Berk can run on just about any mainline, not so a PRR T1.

    A more relevant question would be “where could it run?” The answer to that is – just about anywhere. Unlike the S1, the T1 was designed to operate anywhere on the PRR mainline circa 1942. With the original lateral motion configuration, the T1 could negotiate 16 degree curves, and according to the timetable, could operate in areas where even the M1 was restricted. A specific problem with 130 lb no.8 switches prevented them operating through Pittsburgh – but an increase in lateral motion in 1946, and track realignments in the modern era (required to handle longer freight cars than the 1940’s) mean that this particular issue has been resolved. Based on the revised lateral motion, and the overall dimensions, we’re confident that the T1 can operate anywhere on the current mainline network that the N&W J class can. As part of our project, we will investigate a further increase in lateral motion to allow negotiation of 20 degree curves, which would let the T1 operate on any track currently accessible to a NKP Berkshire. At this point in time, the Trust does not have an agreement in place to operate the locomotive on any class 1 railroad. We will attempt to secure support from a Class 1 carrier once the project is further along. The T1 Trust has received letters of intent from three well established tourist railroads; the Steamtown National Historic Site in Scranton, PA, the Steam Railroading Institute in Owosso, MI and the Cuyahoga Valley Scenic Railroad in Independence, OH. All three of these fine organizations are experienced in handling mainline steam locomotives and can easily support the operation of the T1 locomotive when complete.

  • Where in the USA may the T1 run beyond 120 mph with a decent train consist?

    Presently there are only two possibilities, neither of which is likely for revenue service – The USDOT test loop in Pueblo, and portions of the Northeast corridor. The DOT facility is where we would intend to perform high speed testing to confirm the locomotive’s tracking qualities and top speed potential, with an instrumented test train, and only in compliance with all applicable DOT regulations. High speed running is not necessarily part of the routine service plan. Our intent is to maintain schedule on whatever railroad is willing to host the locomotive for excursion service. We anticipate this will be limited to 79mph top speeds on one or more of the Class 1 railroads. If, however, Amtrak can be persuaded to allow excursion trains on their system, we would plan on operating at speeds of 85-110 mph plus to match their timetable.

  • Did the PRR T1’s ever get east of Harrisburg?

    We haven’t researched the full service career of the T1 fleet, so we can’t say for certain how often it happened, but the answer is definitely yes. 25 of them were built at the Baldwin Locomotive works in Eddystone, PA, just south of Philadelphia, and there are references to one being displayed at railroad equipment shows in Reading PA, and Asbury Park, New Jersey. T1 #5542 was assigned to pulling train No. 17 between Broad Street Philadelphia and Pittsburgh station at least once. However, there was little need for the T1 to run east of Harrisburg, as that region was electrified, and blue ribbon trains were serviced by the GG1.

  • It’s said that the poppet valves had some metallurgy issues that made them a real problem to use at speeds above 100mph but yet at the same time that crews would routinely bring the locomotives up to very high speeds to make up for lost time resulting in very expensive maintenance bills. Would you plans involve fixing those issues?

    From what we’ve seen, the PRR solved this problem by 1947, by changing the valves from mild steel to a higher strength alloy that was better able to cope with the fatigue issues at service speeds. We will run durability and fatigue simulations for speeds in excess of the T1’s rumored top speed, and select alloys and manufacturing processes to maximize reliability.

  • What caused the wheel slippage issues the locomotive had and what if anything could be done to rectify this if you were to build another one today?

    The wheel slip issue had two root causes. The first was ineffective spring equalization. As originally designed (engines 6110 and 6111), the engine truck was not equalized with the drivers, and all four pairs of drivers were equalized together. When entering curves or moving over track that was less than perfectly level, weight was transferred off the front engine, causing the front pairs of drivers to slip. This condition was observed at all speeds, and we believe is the basis for the “uncontrollable” reputation the T1 has. The PRR addressed this in the production fleet by splitting the spring rigging in two – the front engine was equalized with the engine truck, and the rear engine was equalized with the trailing truck. The other root cause was improper handling. Engineers assigned to T1s were given no formal training on how to operate them, and their performance was very different than the K4’s most of them were accustomed to. The front end throttle, high boiler pressure, very large diameter steam delivery pipes, and poppet valves combined to make the T1’s very responsive to throttle application compared to a K4. Too much power applied too quickly resulted in wheel slip, especially at speeds around 15-25 mph. We will be performing kinematic and compliance simulations of the spring rigging and equalization to determine whether further improvements in adhesion are possible. We will be applying a wheel slip alarm, so the engineer would be made aware of a wheel slip more quickly should it occur, and reduce power manually. We will also investigate fitting an electro-mechanical anti-slip device similar in concept to that fitted to the Q2, but with more reliable valves and modern electronics, so no involvement from the engineer would be required.

  • Why are you planning to use the Franklin Type B2 valve gear, instead of the Franklin Type A gear originally used on the T1?

    The Type A gear, while effective, presented a challenge with regard to maintenance, especially for the rear engine. To illustrate this, it’s necessary to explain the main features of the Type A system. Power for the gear was taken from a lever attached to the crossheads of both engines. This lever actuated a bell crank, which actuated an adjustable length rod, which was attached to another bell crank, which actuated the input shaft of the gearbox. The gearbox itself was a sealed, cast steel box which was located above (front engine) or between (rear engine) the locomotive frames. Inside each gearbox were two complete sets of miniature Walshaerts’ valve motion, which were immersed in about 30 gallons of SAE 30 oil. One set provided drive for the intake valves, the other for the exhaust valves. Each set of motion actuated a separate output shaft from the gearbox. Each of these output shafts had a bell crank, which actuated another adjustable length rod, which then actuated another bell crank attached to the inboard end of one of the camshafts. The camshafts were mounted in a second sealed box, mounted between the steam chests, and filled with 2 gallons of cylinder oil. The Camboxes then opened and closed the valves, which were mounted in the steam chests. When the gearboxes needed to be serviced, they were very difficult to access. To reach the front gearbox, located on the frame just ahead of the front cylinders, all of the streamlining on the smokebox and pilot had to be removed. The rear gearbox was almost completely inaccessible, and had to be removed via a drop pit for major servicing. The gear boxes weighted about 3700 pounds each, so removing one from beneath a locomotive was no easy task. Once serviced, all of those adjustable connecting rods between the crosshead and gearbox, and the gearbox and camboxes, had to be re-adjusted to keep the valve events square. That’s a total of six rods, whose lengths were specified to the thousandth of an inch, for each engine. The Type B system avoids all of this. Power is taken from a gearbox driven by a return crank on the main driver crankpin. This gearbox is attached via a jointed driveshaft to a matching gearbox on the outboard end of the cambox. There are very few moving parts, no adjustments required, and everything is accessible from the outside of the locomotive without having to dismantle anything. It’s simpler, lighter, easier and cheaper to fabricate, and much easier to maintain. The Type B is also not without precedent on a T1. In 1948, locomotive #5500 was involved in a sideswipe accident with a K4 on the St. Louis division, resulting in heavy damage. Instead of repairing the locomotive with the Type A Oscillating Cam gear, it was rebuilt with the B2 Rotary Cam gear. Afterward, it gained a reputation as being the best of the fleet, by both engineers and maintenance men alike. There is evidence in PRR correspondence that consideration was given to fitting the type B gear to as many as five T1’s, but this idea was not acted upon. It’s reasonable to speculate that, had the T1 not been replaced so quickly by Diesels, that additional units would have been similarly modified.

  • What are the differences between Franklin Type-B and Caprotti? They look very similar.

    Outwardly, they *are* very similar – they both are powered by jointed driveshafts, driven by a gearbox from a return crank on the main driver crankpin. The main differences are inside the cambox mounted above the power cylinders. Both mechanisms are hard to visualize without referencing drawings, but a basic comparison follows: In the Franklin Type B, the valve timing is set by a continuous contour camshaft. Valve opening and closing events are determined by the profile of the cam, which varies continuously along its length. To adjust the cutoff, or switch from forward to reverse, the camshaft slides laterally via the reversing mechanism, thereby presenting a section of the cam profile to the cam follower on the valve stem. The cam follower is a spherical bearing that makes point contact with the camshaft. The valve timing is controlled by the shape of the camshaft where the follower makes contact. In the Franklin system, the cam follower acts in direct line of action on the valve stem, which is oriented horizontally, parallel to the piston rod. Valves are closed by coil springs acting on the valve stem. In the Caprotti gear (British Caprotti specifically) a variable geometry cam assembly is used. Essentially, there are two very similar cam lobes for each valve, each on separate concentric shafts, which can rotate relative to each other. To adjust the cutoff, or switch from forward to reverse, the angle between the two adjacent cam lobes is altered via a worm gear and crank assembly. The cam follower is a cylindrical roller that makes line contact with both cam lobes simultaneously. The valve timing is controlled by the combined shape of the two cam lobes where the follower makes contact. In the Caprotti system, the cam follower acts via a bell crank on the valve stem, which is oriented vertically, perpendicular to the piston rod. Valves are closed by steam pressure acting on the valve stem. In both cases, the camshafts are mounted parallel to the driver axles, and operate hollow, double seat poppet valves. When the valves are open, steam passes around and through the body of the valve. There are detail differences in the shape of the valves between the two systems, but they are generally similar in design. The rotary cam T1 uses a derivative of the Franklin Type B system, called the B2. Unlike the Caprotti system, which uses one cam assembly to operate both intake and exhaust valves, the Franklin B2 has two camshafts – one exclusively for intake valves, and a second one just for exhaust valves. Also, the B2 has 4 valves (2 intake and 2 exhaust) where the Caprotti has 2 (1 intake and 1 exhaust) at each end of the cylinder.

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