King & Castle Slide Bars

One for the GWR boys. What are the vertical links between the upper & lower slide bars for on Kings & Castles? They are close enough to the motion bracket to make extra support unnessesary in my mind. It has been suggested they would retain the connecting rod if the crosshead pin failed.

Any Suggestions?

PT

 

You mean something like the bracketry on this Polish loco. Obviously dropping a rod on this single slidebar design would have disasterous consequences if the rod hit the deck.

 

I believe they are purely there for support to help maintain the parallelism between the two slide bars at the far end of the piston stroke. Castle and King slide bars are very long and this stay just helps tie them all together in the middle to keep their shape. If you look at 6201 you will see this design was carried over to the first 'Princess' class locos but when the motion bracket arrangement was changed and slide bars shortened it was done away with. If they were there to retain the connecting rod should the gudgeon pin fail why only fit them to Castles and Kings?

 

I doubt that such a flimsy bracket would retain a flailing connecting rod at any speed. Likewise that system on the Polish locolooks more like a reciprocating drive to either a pump or mechanical lubricator; it certainly isn't sufficiently robust to support the weight of a static connecting rod.

 

I saved the picture & zoomed in on it, although it goes very pixelated it looks like a fixed bracket. The "inner" vertical bar protrudes above the connecting rod so I do not think it is attached to the con rod..

 

These are tie bars or clips as we call them. They are fitted to prevent vertical deflection of the slidebars due to the varying vertical loads imposed by the crosshead resulting from the vertical component of the forces in the connecting rod/piston assembly when the connecting rod is at an angle to the horizontal. Such forces tend to increase as the length of the connecting rod decreases, and as such the Star/castle connecting rods are noticably shorter than those fitted to GW Loco's such as the Halls for instance. It should also be noted that the 2 cylinder engines have their slidebars supported towards the middle of the bars where such vertical forces are at thier greatest.

The early Star class engines did not have the clips, but it is evident that several different styles of plain and fluted slidebars were tried and that there was some difficulty with slidebar deflection, and this ultimately led to the Stars quite quickly being fitted with clips to restrain the deflections, later batches of the class being fitted from new. Thereafter the clips became a feature of all GW 4 cylinder engines as well as the first two Princesses which replicated the arrangement. As an aside it is a well known fact that these 2 engines suffered from a high incidence of hot crossheads in their early years, 6200 running hot on its maiden voyage to London for Director's review, and 6201 doing likewise on the down leg of its epic 1936 test run.

The slidebars fitted to the Castles are not the easiest thing in the world to set up accurately and the fitting work requires some painstaking effort to achieve good results. Having aligned the slidebars the clips have to be filed to achieve a fit where they are able to tightly grip the machined recesses provided for them in the slidebars, before the bolts are fitted. When re-fitting reground slidebars, it is usually necessary to heat and "jump" (shorten) the clips so that they are able to be fitted accurately across the reduced dimension across the seatings. Failure to seat the clips properly will usually result in their bolts loosening and the clip seatings wearing if not attended to properly.

Hope this helps
regards
Bob

 

As a follow up to Bobs comments above. I recall during the early stages of 5029's rebuild at Didcot we had a set of tie bars stamped 5043 - the outside slide bars were stamped 5029. Then one day a visitor gave us one odd tie bar stamped 5029 .... a few weeks later a roving pair of eyes spotted the remaining three..... suffice to say that 5029 now has its original set as does 5043.