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Accucraft GS 4 Chimney&Petticoat

2205 Views 8 Replies 4 Participants Last post by  Charles

After carrying out some of the modifications recommended for the alcohol-fired version of Accucraft's GS4 (incl. Gordon Watson's combination levers and nozzles and new wick material) I am still not REALLY happy. The performance is quite OK but could be better.
So I referred to some textbooks and articles on the subject, e.g. Martins Evans' books and J.v. Riemsdijk's articles in the G1MRA Newsletter.
As regards the front end, i.e. arrangement of nozzle, petticoat (chimney extension) and chimney, both authors recommend the same geometrical dimensions. I built two templates to check these dimensions on my Accucraft GS4, see first picture

The template tapered 1:6 governs the height of the chimney top above the nozzle, which appears to be OK, see second picture

However, after applying the second template tapered 1:3 which determines the extension of the petticoat, it appears that the petticoat is at least 1/4" too long!

How's this? This template has 8 stripes green/yellow each 7/64" wide. The template shall sit in the blast nozzle with the tapered part still inside the chimney extension or petticoat by about 3/16". So at least six of the eight stripes should show underneath the petticoat, however, on my GS 4 only three and a half are not covered by the petticoat. That means it is too long and most likely impedes draft!
Has anyone else observed this?
Has anyone unscrewed the petticoat? How is it fixed? I would like to shorten it to make another test.

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Thanks for the hint! Did I miss something here? What's the dimension for the reducing bush? Was this stated in your instructions for the combinations levers, too?

I changed the blast nozzle that was included in your package, but haven't modified the blower nozzle. I have no problems in raising steam, howver, while running I can't get over 50 psi with whatever train. I would like to see the safety valves release some steam at least once in a while to ensure to generate enough steam.

Anyway,  Aster locos raise the bar!


The arch has yet to be installed...

That' s one of the reasons why I consulted the 'classical' sources: before venturing into 'fancy new areas', I wanted to make sure that the 'basic' design rules have been complied with.

Talking about 'fancy new areas': in one test run I had replaced the asbestos(?) wick sheet with fine stainless steel wire mesh - and nothing else! Each burner could only to be ignited by heating it with a miniature soldering torch from underneath until enough Meths had evaporated. This type of burner 'worked' , too, but the impact on the running qualities was at best marginal.


Yes, I downloaded all the threads on the topic I could find, but it looks like I missed the one with the reducing ring (now, after re-reading the instructions provided with Gordon's kit, I see that he mentions the ring , too ).

I'll tackle these last mods over weekend.

Thanks to all for the help.

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