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speedy valve gear and drawings

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fizzy06/01/2013 20:37:49
1706 forum posts
115 photos

Ive been given a complete set of speedy castings and drawingd. The drawings are very old, so if I buy new drawings are the castings likely to tally up with them? I also read about the valve gear being suspect - whats the truth??

Stub Mandrel06/01/2013 21:08:40
4307 forum posts
291 photos
1 articles

>whats the truth??

Face it - you're a lucky b****d!


Speedy Builder506/01/2013 22:02:00
1988 forum posts
139 photos

I am slowly making a 5" Speedy and I know of another builder on this site. I don't think that the castings are a problem, but id you work to Don Ashton's modifications, you must look out for sheets 1A and 2A even then some of the valve gear dimensions I think are wrong.. Look up SPEEDY on this site. Bob

6196206/01/2013 22:59:33
65 forum posts
1 photos

My understanding is that there is little wrong with the LBSC valve gear design, other than he never drew the valve gear quite as accurately as he would have done for the engines he built himself. I've seen plenty of Speedys with LBSC valve gear working well enough.

The main reason for Don Ashton's modified design was to make the gear prototypical, since the GWR 1500s had no drop link from the crosshead as has the LBSC design, the union link being connected directly from the gudgeon pin end to the bottom of the combination lever.

As for the drawings, old as they are I suspect that they, in common with the rest of the Model Engineer published drawings, have never been modified or corrected and the available castings will be as appropriate as they have ever been.


duncan webster06/01/2013 23:51:42
2549 forum posts
49 photos

If valve gear is built to LBSC dimensions the maximum cut off is quite small, which can occasionally give rise to difficulty starting. Both KNHarris and Don Young have published modifications to give longer full gear cut-off.

julian atkins07/01/2013 22:01:16
1235 forum posts
353 photos

the original LBSC valvegear is fundamentally flawed. it was so bad that ME commisioned KN Harris to re-design it, and separately Reeves commisioned Don Young to re-design the valvegear too.

don ashton's re-design corrects errors that neither K N Harris or Don Young completely corrected, and was published in EIM. i would strongly recommend following don ashton's re-design.



Roger Froud06/11/2013 10:18:08
27 forum posts
14 photos
Posted by 61962 on 06/01/2013 22:59:33:

The main reason for Don Ashton's modified design was to make the gear prototypical, since the GWR 1500s had no drop link from the crosshead as has the LBSC design, the union link being connected directly from the gudgeon pin end to the bottom of the combination lever.


I think you're mistaken about the motivation for Don Ashton's reworking of the valve gear. It's true that the Union link isn't correct on LBSCs design, but it's the fact that it radically changes the performance that prompted it being moved back to where it should be. Don has hopefully come up with the best geometry based on modern simulations and years of experience, and that's the pattern I'll be following.

nipper07/10/2014 18:51:27
31 forum posts

i seem to be coming into this forum rather late but I would like to know which Speedy valve gear design requires the minimum of changes to the original and where can i find a copy of the Don Ashton design.


julian atkins07/10/2014 23:41:46
1235 forum posts
353 photos

don ashton's superlative re-design requires the minimum of changes and was published in EIM in 2009.

have a look at roger froud's excellent wiki site here which has don's dimensioned drawing

there is also roger's fascinating and informative build thread on

which already runs to 119 pages!



Edited By julian atkins on 07/10/2014 23:42:15

nipper09/10/2014 22:44:59
31 forum posts

Thanks Julian for leading me to Don's Speedy dimensions. It looks as if I need to make a new drop link, combination lever, radius rod, return crank, lifting arm and maybe move the gear frame. A lot more than I hoped for. I think my cylinders have already been moved forward so that's OK but there is still a lot of work bearing in mind I have all of these parts already made as I am overhauling (bringing back from the dead) a finished chassis. Don's dimension drawing is not very clear but i managed to work out the imperial dimensions by converting the metric drawing back to imperial. Two dimensions were not covered on the metric drawing, the valve head width and the position of the expansion link to eccentric rod attachment. I could not decipher these from the drawing. I assume also that Don does not require any changes to the expansion link size or radius. It would be a great help if these dimensions are available.

Cheers Dave Murray

Edited By nipper on 09/10/2014 22:46:23

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