Roundhouse Hackworth Valve Gear

[HereticUK]

Does anyone have any experience using this? I would like to know their thoughts on it; is it a worthwhile investment? Also from pictures it seems like it is tooled for specific locomotives... I have seen a couple of Berties with HW gear but no Millies (for example). Is it possible to fit it to a Millie?

[DLRdan]

I don't think it is possible to fit it to a Millie as the combustion chanber is in the way of the weigh shaft brackets. It would also mean the weigh shaft runs though the fire.

[HereticUK]

So, basically any engine with an externally fired boiler cannot have the Hackworth valve hear, right?

[TonyW]

So, basically any engine with an externally fired boiler cannot have the Hackworth valve hear, right?

Meths-fired Roundhouse Pooters did. The shaft passed through the flames. Just visible here:

I do not know whether it would be possible with a Millie.

[Keith S]

I'm fairly curious about this myself. On Roundhouse's website they state that the special cylinders with the 3 degree slant are required with the Hackworth valve gear. Yet I've seen pictures of Bertie engines with this valve gear. So have the cylinders been changed? Because eif that was the case the frame would have had new holes drilled for the cylinders in a different position wouldn't they? Or is there enough leeway in the mechanism that regular non-slanted cylinders work "well enough" with the Hackworth gear?

I would very much like a Bertie with this valve gear, but I am confused about the issue of the slanted cylinders. It would require fairly major surgery if they were required.

[HereticUK]

Meths-fired Roundhouse Pooters did. The shaft passed through the flames.

Is that safe? I guess it is otherwise they wouldn't have done it... Don't Meths burn at a higher temperature than gas? If so, what's stopping an adaptation for the Millie? Apologies if these are stupid questions...

And Keith has a point: any Berties I have seen with this attached seem to have the standard cylinders, but on RH website it comes with slanted cylinders...

[TonyW]

On Roundhouse's website they state that the special cylinders with the 3 degree slant are required with the Hackworth valve gear.

An interesting point. Pooters had horizontal cylinders, but the later Carries had the inclined cylinders.
Pooter:

Carrie:
[/img]

[laalratty]

I'm sure Dan has said in the past that he managed to fit the Hackworth gear to his Bertie using the original cylinders. It certainly adds something to the aesthetics of this loco in my opinion, and it runs well too, having been lucky enough to see it running at Elsecar one year.
Fitting Hackworth to a Millie sounds like a challenge that someone out there might like to have a go at.....

[GTB]

I would very much like a Bertie with this valve gear, but I am confused about the issue of the slanted cylinders. It would require fairly major surgery if they were required.

Fitting a Bertie with Hackworth gear involves major surgery anyway, as we aren't talking plug 'n play. The frames are too shallow for fitting Hackworth as they come and need modification of some sort over the rear axle to mount the weighshaft. Adding the sloping cylinders only involves drilling two more holes in each sideframe.

If the standard horizontal cylinders are retained with Hackworth gear, it just means the valve timing will be slightly different between forward and reverse, due to valve rod angularity. The valve rod is long, so the timing difference will be small and I doubt there'd be any noticeable difference in performance on the track.

Graeme

[steam4ian]

Graeme

Hackworth gear has a slight asymmetry inherently due to the short eccentric rod. The offset to which you refer may partially correct that.

If you can't get the slide high enough you could always try Heywood gear which is behind the axle.

Ian

[GTB]

Hackworth gear has a slight asymmetry inherently due to the short eccentric rod. The offset to which you refer may partially correct that.

I suspect the effect of a short eccentric rod is minimised in the Roundhouse design, as their valve gear has minimal lap and no lead, so the valve rod pin is very close to the die block. At least most Sm32/45 locos don't have springs, so the valve events won't wander around due to that.

Little locos are very tolerant of valve events in any case and things have to be a long way out before they stop working.

I'm not a fan of Hackworth gear on aesthetic grounds, but it works well enough. Certainly no worse than 'simplified Walschaerts'.

If you can't get the slide high enough you could always try Heywood gear which is behind the axle.

If someone really wanted a Millie with cab reversing and a weighshaft that went nowhere near the burner, the one I'd use would be the Tayleur-Wheldon gear that Jack fitted to his later Pooters.

Again, I don't think it matters much. A lot of Archangel locos have the spirit burners threaded around inside valve gear of one sort or another and they keep on keeping on......

Graeme

[Clinkard]

Sorry another thread I've come to late (make note to self, look at this forum more frequently).

Hackworth gear does not 'require' cylinders to be either level or inclined. The important point is where the weigh shaft is situated. With the axle in the normal running position, a line drawn through the centre line of the cylinder should pass through the axle centre. The weigh shaft should then be situated on a line drawn at right angles to the first line, also passing though the axle centre, which, if the cylinders are inclined, will mean that the weigh shaft centre will be behind the rear axle.

[Keith S]

So I suppose if one were to use the Roundhouse Hackworth gear as supplied currently, and put it on a locomotive with regular cylinders, then it would simply be a matter of ensuring the weigh shaft is directly over the rear axle, and the adjustable spindle on the valve itself could be screwed in until the rod was the correct length.

One day I will convert a "Bertie"... I don't think this valve gear looks nice on all locomotives, but I do like it on "Bertie".

[steam4ian]

I would recommend putting you dimensions into Charlie Dockstader's valve gear program. see http://www.billp.org/Dockstader/ValveGear.html

The best place for the weight shaft may not be directly above the driving axle, depending on how oblique the valve rod is to the valve spindle.

Regards
Ian

[Keith S]

That sounds like a clever program.

[Clinkard]

The best place for the weight shaft may not be directly above the driving axle, depending on how oblique the valve rod is to the valve spindle.

Regards
Ian

Sorry I don't agree, The weigh shaft position must be correct or all the other dims/alignments are thrown out. That doesn't necessarily mean that it wont work at all, but not perhaps to it's best. What aligns the valve rod to the valve spindle, is the bearing positions on the vibrating link.

[steam4ian]

Clinkard

You have every right to your opinion.

But your rule of thumb is not appropriate to inclined cylinders and may not be so if the valve rod or valve spindle is significantly oblique to the line of the cylinder axis.

Ian

[Clinkard]

If the angle I described above does not equal 90 degrees then what occurs at one end cannot occur the same at the other end of the cylinder, as the piston timing is then different to the valve timing.

Therefore it is not a "Rule of thumb" but a necessity.

EDIT :- My apologies for the typos (late night).