Garden Railway Forum

What's the difference between the two?

I believe Roundhouse changed the design of cylinders used on most classic series locos (Lady Anne, Katie, etc) some time ago.

I can only see a visual difference from the photos I look at of older locos. I only know that you have to specify what type of service kit you want when ordering (old or new style cylinders).

tom_tom_go wrote: ↑Sun Apr 15, 2018 9:16 am What's the difference between the two?

I believe Roundhouse changed the design of cylinders used on most classic series locos (Lady Anne, Katie, etc) some time ago.

The difference is mostly in the valve chest. The current valve chest design is square in plan externally, with a circular cavity, a circular valve and o-ring seals.

The older valve chests are rectangular in plan and aren't flush with the cylinder block along the side. Internally the valves are rectangular and the valve chest uses gaskets instead of o-rings to seal the valve chest. The slide bars are different as well. The step between cylinder block and valve chest is obvious and a marker for the older type of cylinder assembly.

There's a third and even older cylinder assembly used on early Lady Anne and Dylan models that also has rectangular valve chests, but a smaller cylinder bore of 1/2" dia instead of the later and still current 7/16" dia.

Regards,
Graeme

Thank you Graeme for explanation.

Are there reasons not use the older type cylinders anymore?

tom_tom_go wrote: ↑Sun Apr 15, 2018 10:03 am Thank you Graeme for explanation.

Are there reasons not use the older type cylinders anymore?

No technical reason that comes to mind and Roundhouse still support the older design with maintenance parts..........

I think the current design appeared with the Basic series, so it's probably quicker to make and assemble, keeping costs down.

Graeme

I reckon that the new style have better exhaust clearance than the old. My coal-fired Jack running at 60psi used to fight itself with old-style cylinders ... above a certain point the more regulator it had the slower it got and the more noise it made. I swapped old for new and it transformed it in to a lovely free-running loco.

TonyW wrote: ↑Sun Apr 15, 2018 4:08 pm I reckon that the new style have better exhaust clearance than the old.

I take it that both types of cylinder assemblies are physically interchangeable then?

The current R/H valves have 0.5mm inlet lap and 0.2mm exhaust clearance, if I measured them accurately. Set up properly, the valve opens the inlet port a little after dead centre and doesn't close the exhaust port until after dead centre, but just before the inlet port opens. There's no compression at the dead centres that way, which makes for a free running loco in this scale.

I don't have access to any older style cylinders to measure the ports and valve, but if yours are still in the bits box I'd be interested in the measurements out of curiosity.

Graeme

GTB wrote: ↑Mon Apr 16, 2018 3:41 pmI take it that both types of cylinder assemblies are physically interchangeable then?

They are, but the mounting screws/holes are in different places, see picture attached.

GTB wrote: ↑Mon Apr 16, 2018 3:41 pm... but if yours are still in the bits box I'd be interested in the measurements out of curiosity.

Overhauled and sold long ago ... sorry!

.... but a smaller cylinder bore of 1/2" dia instead of the later and still current 7/16" dia.

Isn't 7/16 smaller than 1/2 ?

Keith S wrote: ↑Mon Apr 30, 2018 5:32 am

.... but a smaller cylinder bore of 1/2" dia instead of the later and still current 7/16" dia.

Isn't 7/16 smaller than 1/2 ?

It's a typo. current RH cylinders are 9/16" dia........