Tangmere

I think poor, uneconomical writing is rather more to do with the teaching of English than the ubiquity of word processor software.

 

Any one got a picture of the small end, gudgeon pin and assembly, for those who know less on these things.

 

I tried to attach a photo but it wouldn't work for me . . .

Take a look at this one - not my photo

http://locoyard.files.wordpress.com...r-winston-churchill-wheels-and-valve-gear.jpg

If the pin remained in one piece the vertical pin/cotter in front of the nut would have either failed or dropped out, the large nut on the gudgeon pin itself could then unscrew, and the gudgeon pin then would need to travel backwards towards the frame to then fall out . . .

I assume if the 'pin was found on the locomotive' it ended up on one the brake hangers - a lucky place for it to end up for the investigators . . .

Hope that explanation helps.

Fergus

 

You need to look at the photo posted on the Capital Christmas express thread (post 165) http://www.national-preservation.co...christmas-express-23rd-november.164731/page-9. 34067 has a different type of small end from 34051. On the earlier style of small end their isn't a safety device to stop the pin from coming out. Looking at your photo of 34051 the oil pot stopping the pin from coming out.

 

There is a locking device. If you look closely there is a castle nut with a split pin. The only comment I would make is that when securing castle nuta on my old Land Rover i would use a much longer split pin and bend it round the nut

 

Mentioned in #108 that the cotter pin was found on the bogie splasher.

 

Starting to edge towards rather dubious speculation here folks. Yes, speculation is great fun and all that, but it gets into risky territory. Interesting that more than one design apparently existed and survives for the component though. Ne interesting to hear about the history behind those variations too.

 

I agree what your saying about a split pin. But on the later style. The split pin can't fall out of the castle nut because the cross head oil pot stops the pin from dropping out. Which must be a later added safety device to stop the pin from coming out. I also see 34007 has the later style of cross head modification.

 

73129, please explain how an oilpot positioned above the cotter stops the cotter dropping out?

 

I would of thought as its a tapered cotter which is driven in from the top, that the only way to remove it is upwards and with the oil pot in the way . . . . . . - although it wouldn't be very secure but at least it can't fall out altogether.

 

The above post by fergusmacg explains how the pin can't drop out because the oil pot is in the way. The split pin is too long to go by the oil pot. I've posted a photo of this below. I hope this shows what I'm on about.

 

Lots of locos have castellated small end nuts. Including the apparently more modern BR Standards.

 

A shot of Tangmere's small end arrangement (driver's side)

http://www.flickr.com/photos/spinner673/4029464666/in/set-72157622451319342

 

i'm a bit confused is the small end on the connecting rod secured by cotter pin or split pin? i always thought it was by split pin what ever the cause, it seems even more lucky that the engine stayed on the rails. so it was the small end and not the big end that came adrift. If the pin was found intact, is there any circumstance that might cause the castle nut to split and either work loose or split totally in half?

 

best advise RAIB not to bother, it will be sorted on here

 

No mention of the cotter pin being found on the splasher. It was the gudgeon pin. Two different things. The cotter pin has yet to be found.

 

Photos of two quite different crosshead/small end arrangements have now been posted. The bottom slidebar on Tangmere appears to be much deeper than the one on 34051. Not being knowledgeable on the finer points of a Bulleid, which is the later arrangement?

 

I don't have experience of steam locomotives, but in the ten years I spent working in the motorcycle trade I saw some astonishingly unlikely and unpredictable failures. I suspect that folk who say "never" or "absolutely impossible" might be either very brave or just a little inexperienced. So, I'd say there are always circumstances, even if no-one can predict them beforehand.

 

Cotter pins is a confusing term. In the US and consequently much of the world, a split pin is referred to as a cotter pin. I presume that you are meaning a flat cotter or a split pin?

 

Round gudgeon pin with thread on outer end passes through crosshead, through the small end of the connecting rod, and then through the crosshead again. The gudgeon pin is retained by a castellated nut, which in turn is secured by a flat cotter pin.

And the cotter pin could drop out of the later style arrangement on Wadebridge if the head broke off the cotter pin