2721 Class:- Chassis Replacement

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woode
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Joined: Tue Jun 05, 2012 12:58 pm

2721 Class:- Chassis Replacement

Postby woode » Tue Jul 10, 2018 4:21 pm

2721 Class Chassis Replacement

The Great Western livery is more typical for the 2721 class and only R2534 (RN 2738) and R2534A (RN 2748) have the improved body, route circles on the cab sides and buffer beam numbers. GWR livery models with the same details are R2328 (RN 2799), R2328A (RN2759) and R2328B (RN 2771).

The non traction tyre 2721 can be improved by removing the tank side weights and filling the tanks and smoke box with lead weights 276g. It seams to stay on the track better, dead spots less and will pull a good load.

The traction tyred version only weighs 174g but will pull a good load forward. They can be jerky in reverse but this is a chassis design problem - replacement is the only solution.

The best chassis to fit is the excellent (32-xxx) Bachmann chassis, with its correct wheel spacing and size, brake rodding and NEM couplings. This chassis does not protrude out of the firebox bulkhead unlike the conversion shown on http://Www.gwr.org.uk, which uses the old split 57xx chassis.

The Hornby 2721 chassis has front to centre wheel spacing of 31mm and a wheel diameter of 19.3mm with no external brake rodding. The Bachmann has spacing of 29mm and 18.5mm diameter wheels.

The 2721 front and centre splashers are 30mm apart so do not quite line up with the Bachmann chassis. The 2721 body is 2mm longer than Bachmann locos but there is no problem with buffer clearance on tight curves.

The 2721 body hole was widened with a router cutter tool in a modelling drill. The hole was made slightly smaller than the space between the original 17g weights. The ribs on the underside of the cab floor and behind the front buffer were removed to leave a flat surface.

The 2721 angled firebox bulkhead is in the way of the Bachmann chassis worm gear. This requires the gear to be shortened and an indent filed in the back of the bulkhead. (The DCC chassis has a smaller worm gear than the non DCC chassis so only needs shortening by 1mm.
The non DCC chassis will need a piece more off the gear. Mount the chassis as far forward in the body as possible)

Unfortunately the 2721 cab floor is in the way of the final gear and some of the chassis frame. The floor was cut to clear the gear and the frame cut down. (This part of frame holds the 8750/57xx firebox bulkhead)

The original 17g weights were removed and replaced with lead weights. The tender, whistle and steam dome were filled with liquid lead, this gave a weight of 230g, using the lighter DCC chassis. (The 8750 is 223g, with the heavier non DCC chassis. There is 20g difference in the chassis)
Attachments
HB 2721 - 2 R.jpg
HB 2721 - 1 R.jpg

Bigmet
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Re: 2721 Class:- Chassis Replacement

Postby Bigmet » Wed Jul 11, 2018 11:50 am

Another neat job to put a more competent mech into a dated model.

It is sobering to realise that the current incorrectly dimensioned Hornby 'universal' 0-6-0T mechanism originated with a 1950s compromise. There's one 0-6-0T mechanism in Hornby's range that they tooled themselves and is correctly dimensioned, that's the recent J50. Wonder how long a wait for a second good 0-6-0T from this manufacturer? Still plenty of prototypes going begging as activity by other manufcturers indicates.

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D605Eagle
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Re: 2721 Class:- Chassis Replacement

Postby D605Eagle » Sat Jul 14, 2018 1:29 am

I slightly modified one that had the sspp Chinese era chassis design by fitting wheels with no traction tyres. Amusingly hornby set the quartering the opposite direction on the non traction tyred wheelsets compared to the sspp ones. I also added pickups on the centre wheel set and some lead in the pannier tanks. It ran surprisingly smoothly, would go over any pointwork due to the rear wheels been sprung and pulled well too. I sold it to somebody on here.

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GeraldH
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Re: 2721 Class:- Chassis Replacement

Postby GeraldH » Sun Jul 29, 2018 11:31 am

D605Eagle wrote:I slightly modified one that had the sspp Chinese era chassis design by fitting wheels with no traction tyres. Amusingly hornby set the quartering the opposite direction on the non traction tyred wheelsets compared to the sspp ones. I also added pickups on the centre wheel set and some lead in the pannier tanks. It ran surprisingly smoothly, would go over any pointwork due to the rear wheels been sprung and pulled well too. I sold it to somebody on here.


I've done the same on several of these Hornby 0-6-0s and with slight tweaks to the springing arrangement, the running is significantly improved.
Gerald H - BNR Correspondent :)

My layout: http://www.newrailwaymodellers.co.uk/Fo ... hp?t=28854


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