User talk:86.133.61.19

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Hello. I have done considerable work the Bulleid chain driven valve gear article and am interested in your recent edit on chain stretch/wear - what actually takes place and what causes the slack - is it wear on the pivot, the link or the cog?--John of Paris (talk) 11:52, 24 February 2008 (UTC)


Thanks for that.

The use of chains is very rare in steam locomotives; they have sometimes been used for coupling the driving wheels together so that they share the effort in traction, and that since very early days (George Stephenson fitted them in 1815).

The Bulleid chain gear in the article was designed by a very original engineer, Oliver Bulleid, who worked for the English Southern Railway from 1937-1949. The chains there took the drive from the driving axle to operate a normal valve gear, the purpose of which is to vary the timing of steam inlet to the cylinders, at what part of the piston stroke to cut the steam off and use it expansively and when to exhaust it. This is all usually done simply by an arrangement of levers and slotted links — there is usually no cam shaft (not a chain-driven one anyway).

Bulleid has had a lot of flak, especially for his valve gear from other engineers and writers then and since, and it is true that the engines fitted with the chain-driven gear were very temperamental, most writers attributing this to chain stretch. What I was trying to point out was that there were other more important issues with the geometry of the valve gear itself (proportions of the levers etc.) that were more likely to have been the cause of the trouble and your comments give water to my mill.

What you say about the automatic (it would have to be fully automatic) tensioner had occurred to me as one of the most interesting benefits of the chains is that the drive of the valve gear derives from a fixed pivot; if it comes from the axle, the latter has vertical up and down play to adapt to irregularities in the track and disturbs the timing. This means that some sort of sprung pivotal movement should have been given to the idler gear - which it wasn't.

I suppose I am rewriting history, but I have my own hobby horse that for certain uses, updated steam technology could still have a place in the future. The problem is that most people today, including engineers (and steam buffs), have an extremely hazy idea of what it actually is.

- By the way, if ever you should decide to sign up to Wickipedia, do drop a line on my talk page.--John of Paris (talk) 12:37, 25 February 2008 (UTC)

Thanks for the added comment. It's getting a lot clearer now. You'll notice that I did revert one of your edits as, rightly or wrongly, it has been put down to chain stretch by numerous writers. But it may all need expanding upon. I'll sleep on that... Cheers,--John of Paris (talk) 18:36, 27 February 2008 (UTC)