Outside Bearing vs. Inside Bearing?

[daveklepper]

I believe the Manor class was the last G.W. steam in service, because it was light enough to a few places where the then diesel fleet was to heavy, or was it because of some other reason?

[M636C]

There were three classes of 4-6-0 on the Great Western that would have been used on freight services:

These were:

the Hall class with 6' driving wheels

the Grange class with 5'8" driving wheels

The Manor class which was basically a Grange with a smaller boiler for lighter track...

It is worth pointing out that while the trailing axle on the King bogie had to clear the outside cylinders, the leading axle had to clear the two inside cylinders, hence the position of the springs. Holcroft, who had left Swindon by that time indicated that the King bogie design was submitted more or less as a joke by a draftsman who couldn't think of any alternative.

The other four cylinder locomotives (Star and Castle clases) used a bar frame truck with beam equalised axles with a semi elliptic spring located each side between the axles. This provided adequate clearance for both inside and outside cylinders. It isn't known why Collett wanted independent springing but in the LMS Princess which had exactly the same cylinder layout and sizes as the King, Stanier used the bar frame design. Since the Princess was heavier, that can't have been a problem.

The original truck design on the King had some problems with detail design of the suspension, and modified springs were fitted to King George V while in the USA for the "Fair of the Iron Horse" in 1927.

M636C

[daveklepper]

Thanks.  Were not some Great Western 4-6-0's also used on freight?

[ACY Tom]

The Great Bear (Great Western no. 111) was built in 1908.  She was the first Pacific in England, and the country's most powerful express engine of the day.  Because of her weight, her operating territory was restricted, and she was never duplicated.  The G.W.R. reverted to the use of 4-6-0's for passenger and express service, and the Great Bear was converted to a 4-6-0 in 1924 and renamed Viscount Churchill.  She was retired in 1953. 

Tom

[Wizlish]

King class is 4-6-0.  Since there is only one truck, 'rear truck axle' is the back axle in the truck, the one that has to clear the crosshead and guides, and the forward truck axle the one ahead of the cylinders. 

Note that I purposefully avoided using the words 'trailing' or 'leading' axle in referring to these two axle positions within a rigid-frame (Adams) lead truck.

The Great Western did indeed  have  a locomotive with a trailing truck -- a rather famous one, named for a famous constellation.  Can you name it and describe its significance?

[daveklepper]

Did not know that the Great Western had locomotives with trailing trucks.  What was the Kings' wheel arrangement?   2-4-2?   2-6-2?   When built?  Swindon?  When last used?  If they were tank engines, it would be strange to be referred to as Kings.

[Trainman2001]

That's what I call a complete answer. Thank you! It gave many more points of thought in their choice than I could come up with. It probably had something to do which department had the most influence...operations who wanted speed and stability and maintenance who knew all these machines needed servicing often and wanted to expedite things a little. I'm conjecturing here...

[Wizlish]

Trainman2001

While the Wootten vs. Belpaire is a preference, there are differences that can lead to this preference. Belpaires were easier to manufacture since most of the inner and outer surfaces were parallel. Since Pennsy made a lot of their own engines this could have been one of the factors they considered. Wootten boxes are a bit sturdier since all those flat Belpaire surfaces made staying even more critical.

Don't confuse Wootten (which is specifically optimized for anthracite or culm firing) with a typical radial-stay or wagon-top boiler structure.

My understanding was that Belpaire wrappers were harder to fabricate due to the complicated shape at the hips and corners, the advantage being that all the crown stays were not only the same length, but at reasonable right angles to both the crown and wrapper.  There is also some additional circulation space above the water legs, although I do not know if this has actual advantage for vertical circulation - note the vaunted advantages in both firebox and chamber for Lima's "Double Belpaire" but also the staying required. 

In a radial-stay box the curve of the crown sheet is very different from the outer wrapper, so some fun geometry is required to figure out the forces and angles to be reamed and tapped for the staybolts.  Pressure (and cracking tendency) is better handled on the radial-stay wrapper - no corners - but the staybolt bending forces are more complex.

But, I still don't know the advantages or disadvantages to inside vs. outside bearings. I imagine that servicing the outside bearing pony truck would be easier.

I had thought by now you'd have had a better answer.  There are a number of advantages to one or the other, and I won't pretend to provide you with either a comprehensive or objectively correct list.  But here are some points:

The outside-frame truck was understood to provide better roll stability, and of course makes it easier to maintain bearings and replace wheelsets.  It has a somewhat higher overall weight, and in my opinion a higher polar moment of inertia in yaw, but some references indicate it is preferable for high-speed use (the PRR T1 being provided with outside-frame and the NYC counterpart design C1a also having it despite the Niagara and other NYC practice being inside bearing).  However, that does not mean inside-bearing high speed design was a compromise -- the Milwaukee A and F had inside bearings, and the Santa Fe Batz truck neatly managed things. 

For high speed and stability in a TWO-wheel lead truck, the best designs were almost necessarily outside-bearing ;it was much more difficult to provide the necessary levers for three-axis control and suspension with an inside frame, as well as to provide progressive weight transfer for swing return.  Obviously there were plenty of locomotives that ran effectively with an inside-bearing Bissel, but the outside bearing design, particularly with cast frame as in late N&W practice, was a better approach.

Roller bearings were more complicated to accommodate in an inside-bearing truck, and wheels had to be pressed on and off with the bearings still installed.

Animportant consideration that isn't always recognized is access to pistons and cylinder bores, and ease of replacing a cylinder head.  A typical inside-frame truck clears the whole end of the cylinder, whereas an outside-brame truck may have to be removed, or the locomotive jacked up, in order to get the piston and rod out, or to install or finish liner bushings,etc..  Conversely there can be more clearance between the rear of a four-wheel inside-frame truck and the crosshead guides, etc. when the truck swivels.

There is at least one famous class, the Great Western Kings, which had the rear truck axle inside-bearing and the forward one outside-bearing - a strange-looking arrangement to say the least!  Trains had an article that documented the specific reasons why this was done.

[Trainman2001]

While the Wooten vs. Belpair is a preference, there are differences that can lead to this preference. Belpairs were easier to manufacture since most of the inner and our surfaces were parallel. Since Pennsy made a lot of their own engines this could have been one of the factors they considered. Wooten boxes are a bit sturdier since all those flat Belpair surfaces made staying even more critical. But, I still don't know the advantages or disadvantages to inside vs. outside bearings. I imagine that servicing the outside bearing pony truck would be easier.

[ndbprr]

Since the engines mentioned were probably contemporaries both bearing types existed. That would lead credence to the choice being a preference Just like the Pennsylvania Railroad preferred Belpaire boilers while others preferred wagon top boilers.

[Trainman2001]

Can anyone explain why some engine trucks were inside bearing where the entire wheel was exposed or outside bearing where you had castings, journal boxes and equalizer bars showing and the wheels were buried within? Was it road preference or was there some distinct advantage of one style over another? Example: Pennsy J1-a Texas had outside journal engine truck whereas the Santa Fe version of that wheel arrangment has inside bearing.