Tangmere

One thing of note was the observation that 34067 is owned by an associate company which has an operational engineer trusted to ftr on behalf of wcr which was contrary to the SMS of wcr. Is this unique to 34067 because of the closeness of the ownership to wcr or common to all externally owned locos used by wcr?

 

True, but it did contain that potentially-ominous "120 ... b. There was nothing to prevent the connecting rod dropping to the ground after the small end joint came apart", which could have led to a recommendation that only locomotives with such arrangements be allowed on major lines on the national network, or something like that. So I think a bullet was dodged...

Noel

 

I hope that "they" don't read that and say "now there's an idea..."!

Steve B

 

My understanding is that what they are concerned about in relation to the SMS is not the employment status of the engineer, but that the same person was both doing the maintenance certification and the FTR examination - one set of eyes rather than two.

 

That would be my assessment as well. My question is whether the single set of eyes is unique to Tangmere or standard practice? There must be quite a small pool of competent persons which must make it difficult at times to avoid the scenario of 34067.

 

Interesting that they looked at an incident in Australia, I wonder if they looked other countries nearer to home.

The only reason I make the comment is that in steam days in Western Germany the Class 01s and 52s and possibly others had a bracket which would have held the rod clear of the track in the event of a small end failure. Whether this was introduced as a consequence of an accident or not I have no idea but would be interested to know.

 

At speed is there belief this bracket is strong enough to hold both the impact stress and weight of the rod ?

There is comment about restorers practice and use of none SR (i.e. LMS/BR/LNER) practice in the overhaul instead of following the design method. Paragraphs 59-61

 

Once disconnected from the piston, there's only the weight of the rod and the the control of the for and aft movement coming from the wheel rotation.

 

At 75mph that's a pretty substantial only...

I think the key thing is the rarity of the incident, something the report puts a reasonable amount of emphasis on.

 

Noel - we are talking a huge number of locos with single slidebars. As well as the Bulleids there are all the LNER pacifics including Tornado, a number of standard classes (4 (4-6-0)-5 - 6 -7 & 8). Lord Nelson and others I cant bother to look up this time of the evening. A question not definitavely answered is would a double slidebar actually contain a flailing rod?

 

If anyone wants a closer look at the standard arrangement (but on the later crosshead design), this is 35028. From the stamped number on the end of the gudgeon pin, I'd say she's been using that pin for around 50 years, and 35028 must have the highest mileage in preservation of any Bulleid.

A long life of the pin doesn't mean anything. I expect it will have had a new cotter every time they took the rods down, and probably a few new nuts too; mere survival only shows that nothing has broken yet. But since 34067 definitely did have a failure in the nut/cotter region, I'd take some persuading to accept that the castellated arrangement was an improvement in the particular case of a Bulleid crosshead. The RAIB recommendation that West Coast should review the benefits/otherwise of the castellated arrangement seems sensible.

 

So what is the position with main line electric units on SWT? Is there an independant set of eyes before the morning commuter run?

 

So would the report writers if I understand them correctly. It seems to me that they are saying that the arrangement ought not to have been approvrd by VAB, although they also make the practical point that it would be nearly impossible for VAB to know that.

An worthwhile sub point is on the value of forum speculation. It seems likely that the root cause was that Tangmere's gudgeon pin arrangement was not of either SR or BR design, but in all the talk, of which I was as guilty as anyone, no-one appears to have noticed. We were blithly rabbiting on about earlier and later designs in complete ignorance of the actual history of the design, which made all our chatter quite worthless.

 

And again reference to my bete noir - materials quality - where at Para 77 it notes "The nut was manufactured at the same time as the gudgeon pin, and witness evidence indicates that it is likely that it was made from the same material, steel to specification EN3b (as defined in British Standard BS970:1955), or a similar grade. This is a mild steel having a tensile strength of around 430 MPa (63000 lbf/sq in, which is lower than the original specification for these components). The use of a lower grade of steel than originally specified, although it may wear more rapidly, is unlikely to have been significant in practice, as the gudgeon pin and nut are not highly stressed."

When I refer to the LMA Handbook (Locomotive Manufacturers Association) it refers to the specification (BS Report 24 Class A or D) for gudgeon pins and nuts as requiring a tensile strength test of 24 - 28 tons (53760 - 62720 lbs) peer square inch for Class A and 40 - 45 tons (89,600 - 100,800 lbs) per square inch for Class D materials. On the assumption that main-line duties would require the higher spec [Class D] I am minded to ask what bearing - if any - the current metal specification has if it is to a lower quality despite the RAIB noting the lower grade of steel but opining that it has no significance in practice when it states "as the gudgeon pin and nut are not highly stressed".

In one respect the report overall refutes this in part by noting that modification of parts needs to be tempered by caution yet it does not consider the parallel of a change in material specifications; is this a point that needs to be considered and investigated further. It may not be relevant when a locomotive is used on heritage lines where stresses will be less and any consequences will be more easily dealt with but on the main line incidents such as that with 34067 may have more serious consequences - and I am yet to be convinced that this aspect is given enough consideration by many.

 

The BR gudgeon pin drawing refers to "steel B R S 102/6" If this is a SR/BR standard spec the actual material required could be discovered if anyone can find the spec

 

As a small aside, just why does anyone consider this arrangement to be "single slidebar"?

There are obviously three, one upper that takes the bulk of the wear load and two lower. A single slidebar has what might be termed a box type crosshead which when assembled fits around the bar.

With a double bar though you can fit links between the two in order to act as lateral restraints to the small end of the rod should it become detached, the application of the same depends on the valve gear arrangement used. How much protection such an application could offer at 75mph is an interesting point. The small end would strike the crosshead and piston rod, be deflected and strike the restraint bars, and so on.

The compact arrangement of the triple bar design has proved itself for decades.

This episode illustrates the importance of understanding design details and why they were used. This horse was nearly lost because of the loss of a nail. The steam movement got away lightly with this one.

 

Not only the horse but the battle and the kingdom. If there had been a derailment and people had died, it would have been politically very difficult to allow business as usual.

 

Material specifications are readily available in the British Transport Commission document "Materials for Locomotives and Tenders 1957"
BRS 102/6 is 24/4/8D which is 970-EN8.

 

I have a saying " If you work to the picture, you can't go wrong."
However, in saying that, I have recently found three errors in B.R. locomotive drawings. Two of these errors are to do with the subject matter being discussed in this thread.

 

Sitting comfortably and with the benefit of hindsight, it is posibly too easy to point the finger at restorers who posibly did not have access to the information we curently have. A mumber of the drawings came via the NRM which arguably did not have the data retreval resource we have.