Handing of connecting rods

Discuss model railway topics and news that do not fit into other sections.
Elmo
Posts: 2
Joined: Thu Mar 04, 2021 9:48 pm

Handing of connecting rods

Postby Elmo » Fri Mar 05, 2021 6:51 pm

Hi everyone, I'd like a bit of advice or help. I've recently got hold of a second hand O gauge Nellie 040 tank, similar to the Southern C14 class. I think it's a Connoisseur model. It's been constructed pretty well, although I intend to re do the paintwork, but the seller did mention that the wheels lock due to not being handed correctly.

I'm a reasonably competent modeller but this is new to me so forgive my ignorance, but am I right in assuming that the connecting rods need to be at precisely the opposite to each other on either side? Ie when one side is at the top of the wheels the other side needs to be at the bottom on the other side? Ir is there more to it?

The model is conventionally powered, in that the motor drives the rear wheels which in turn should rotate the front wheels via the connecting rods. I'd be grateful for any advice, many thanks.

bnb
Posts: 23
Joined: Sat Apr 02, 2011 10:25 am

Re: Handing of connecting rods

Postby bnb » Fri Mar 05, 2021 7:03 pm

Hi
Rods should be 'quartered' if one is at 12 o'clock the other should be at either 9 0'clock or 3 o'clock. One side should lead to be accurate according to the engine being modelled but that is beyond my knowledge so hopefully someone will be able to give that information.

Elmo
Posts: 2
Joined: Thu Mar 04, 2021 9:48 pm

Re: Handing of connecting rods

Postby Elmo » Fri Mar 05, 2021 8:38 pm

Thanks, that's a big help and makes sense. I'll give it a go.

User avatar
Mountain
Posts: 4757
Joined: Mon Oct 24, 2016 3:43 pm
Location: Somewhere in Wales, UK.

Re: Handing of connecting rods

Postby Mountain » Fri Mar 05, 2021 11:50 pm

Quartering is a strange thing. It will work well with one side a quarter of a turn forward or backwards to the other side, but any other angle and it does not work. Most people assume that they should be at equal opposites (180 degrees) but it does not work that way and I don't know why. I tried it as a child, and it was only trial and error and persistance that I learned that I had to put them at 90 degrees. (Yes, I took my models apart and back together from an early age!)

You mentioned though about the con rods being upsidown? On a four wheeled model loco this makes no difference other then visual, but if one has 6 or more coupled drive wheels, and some have a different wheelbase, it obviously will not work if the con rods do not match up to where the inner pairs of wheels are. The outer 4 wheels will always be the same wheelbase and therefore the con rods will line up with those, be they upsidown or the right way up.

I actually had a BR standard class loco body and a tender sold to me at a very low price (It may have been given when I bought other things fromthe man. I don't remember now). But I found that Bachmann sold new motorized chassis so I thought "Ideal". I also bought some Romford tender wheels and I had myself a working 00 gauge loco. The only problem was that Bachmann had put the con rods on upsidown on both sides. I had to take off the tiniest little circlips to remedy the issue. It was a success but I don't fancy doing that again if I can help it!

User avatar
stuartp
Posts: 1203
Joined: Sat Feb 28, 2009 7:40 pm

Re: Handing of connecting rods

Postby stuartp » Sat Mar 06, 2021 1:43 am

If the wheels are locking then either the quartering is slightly out on one or more wheels, or one coupling rod is slightly longer than the other (or the holes are not the same distance apart on both sides), or the axles are not square/parallel.

The quartering needs to be exactly the same on both axles - 90 degrees as Mountain said. It doesn't really matter if they're 89 deg or 91 deg, as long as they're both 89 or 91.

The other two possibilities need accurate measuring to identify.
Portwilliam - Southwest Scotland in the 1960s, in OO - http://stuart1968.wordpress.com/

Bigmet
Posts: 8259
Joined: Tue Aug 14, 2007 2:19 pm

Re: Handing of connecting rods

Postby Bigmet » Sat Mar 06, 2021 10:14 am

Elmo wrote:...the motor drives the rear wheels which in turn should rotate the front wheels via the connecting rods...


So the first test is to remove the coupling rods, (that couple the wheels) and to remove the connecting rods between cylinders and wheels if these are present. Does the mechanism drive the powered wheel smoothly? If not that will have to be sorted out first.

Elmo wrote:...am I right in assuming that the connecting rods need to be at precisely the opposite to each other on either side? Ie when one side is at the top of the wheels the other side needs to be at the bottom on the other side? ...

As already mentioned by 'stuartp' the wheelsets identically quartered is the way, and typically 'right hand lead'; imagine the driver looking out of the right side of the cab, and with the right hand piston at front of stroke, the left hand piston will be 90 degrees behind, midway through its back stroke. (Back in the day this really mattered for the drivers, to know where the pistons were in order to have maximum torque available when starting a train.)

Side note, a problem with 'lead' is that some works went for left hand lead, but you need knowledge of works practise, drawings, or examination of the prototype to determine this.

Mountain wrote:Quartering is a strange thing. It will work well with one side a quarter of a turn forward or backwards to the other side, but any other angle and it does not work...

Sorry, but that is simply not true. But first, 'quartering' (90 degrees) is the simplest and most tolerant setting, and mechanically optimum for a self starting two cylinder machine. It is also far and away the most common in steam loco traction.

However, a quick examination of a three cylinder simple loco will reveal that their wheels were 'thirded' (nominally 120 degrees), and other angular settings are feasible too for multicylinder locos, but very rarely applied to steam rail traction. For anyone interested, if you want your Gresley, Holden, Fowler, Maunsell, Raven, Stanier, Bulleid, Thompson, Peppercorn, Riddles, three cylinder models externally more correct, it is possible to reset the wheels for 120 degrees in OO and larger scales. But this setting is significantly more demanding of precision; so don't expect the RTR manufacturers to take it up; the greater tolerance permitted by quartering will maintain it as their favoured method forever more.

User avatar
Mountain
Posts: 4757
Joined: Mon Oct 24, 2016 3:43 pm
Location: Somewhere in Wales, UK.

Re: Handing of connecting rods

Postby Mountain » Sat Mar 06, 2021 11:09 am

I know that when I tried other angles I could not get the things to work. I have not heard of the thirding of the con rods. Makes me want to try it. :D


Return to “General Model Railway Discussion / News”

Who is online

Users browsing this forum: No registered users and 6 guests