G Scale Model Train Forum banner

Accucraft GS 4 Chimney&Petticoat

2208 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.

See less See more
1 - 2 of 9 Posts
I would guess that you have read our posts on GS4 modifications.  In the post your will see the arch in the firebox.  This one is a simple design held in place by the wick containers.  One could also do a baffle/arch as did Gordon (if I get a chance will post photo).
The reducing ring on the center flue in the smoke box was documented by Dave Hottman long time ago.  Recently we repack a burner set of wick using Gordon's layout of wick material- outstanding fire!  Might be the fuel flow, maybe need an extension adjustment on the sump.

Dave Hottman reference in archives(with contributions from Brooks, John and Andrew):

Try original wick design with arch and restrictor in center flue.
Assumptions...given Gordon kit and the numerous ones we hae done; exhaust nozzle was spot on, so I never questioned that but it would effect the performance.  One can solder the hole and re-drill, 2mm
1 - 2 of 9 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.