Con Rod Screws

[ColinB]

Has anyone any idea why Hornby use different diameter and obviously different thread con rod screws?

I recently changed the conrods on my Tornado to A4 ones as the A4 ones are in two pieces as opposed to the single length used on the Tornado, giving the loco a better ride. When I was fitting the conrods I suddenly realised that the screws were different, although the heads are the same size. I know some of you will see it as knocking Hornby but why? It can't be a "cost save" as they don't make enough of them, plus you have the complication of sourcing two types which negates any cost save. It just seems weird as it means you have to keep several different types as spares.

[atom3624]

There are smaller ones, generally in the centres, and slightly larger on the outer ends of the coupling rods. These latter ones have changed quite a lot in recent years - smaller than before.

Some have a shoulder, some may be smaller, for the tacho cable which some have, which like those in the centre driver of '6-coupled locomotives' screws into the centre of a small shaft, rather than directly into a socket in the wheel.

Details appear to have been finer, less cumbersome in the later years - that big shaft sticking out for the tacho cable is now quite a bit smaller, more 'prototypical' shall we say.

I think it's simply to try and advance the detailing.

Al.

[96RAF]

Likely some models are legacy Imperial thread screws and newer ones are metric. Progress like kgs from lbs.

[ColinB]

No it is none of those. Yes I know the centre one is thinner with no shoulder as it holds on the valve gear, unless it is an original West Country or Merchant navy then it is one with a very long shoulder. There are also thin ones for holding on the speedo or pump, but that is reflected in the wheel having an insert as is the case with the centre wheels. These are thin shouldered ones that only seem to be used on the Railroad Tornado, they don't even seem to use them on the Railroad Mallard. It is not even the difference between metric and imperial, I have some of the old imperial ones, they are totally different. I assume some designer thought they might save some money. I have the Bon Accord and a Tornado locos that use the same chassis, which seems to also use the singular con rod, 3 pole motor and small diameter con rod screws. I don't know if the latest Railroad Mallard is the same, most of the earlier Railroad A4s I have, use the old chassis with slightly "chunkier" valve gear.

[atom3624]

The Lord Nelson speedo is much-closer mounted, with no spacer - the insert barely stands proud of the wheel.

Al.