Hornby Rebuilt Royal Scot mechanism.

[ColinB]

This is just meant for discussion. The chassis on my Rebuilt Royal Scot suffered from the dreaded Mazak rot, on the chassis, and motor mounts. I was able to get a secondhand chassis and motor mounts but still the motor kept disengaging. Anyway looking at the way the motor is clamped in, I decided to modify it so it worked better, this involved making the clamp sit more vertical. Sure enough it did. Fast forward a year and suddenly Peters Spares has new chassis available. So last night I swopped everything over to put it back to the original motor setup, but still the motor slips, so I reverted to my modified design.

Can anyone explain to me why Hornby went for such a complicated design? It is sort of a cantilever that puts undue stress on the post and doesn't work very well, as the clamp is angled so difficult to clamp the motor properly. I did wonder if it was so under the boiler was a clean profile, but looking at mine I am not even sure that is correct. So any ideas why it is like this? It is definitely not for cheapness.

[96RAF]

Got a service sheet to refer to Colin, as I don’t have a loco to look at. I wonder if the design has been used on other variants.

[Ruffnut Thorston]

Service Sheet HSS 429 Royal Scot Class from 2017.

Motor area...

[Going Spare]

305 and 429 cover the rebuilt Royal Scot.

[ColinB]

I don't really know if the design was used on other variants, definitely not on any of the locos I own not even the unrebuilt Patriot Railroad model. The trouble is the more I look at it the more it looks wrong. Trouble is as you screw down on the screw (self tapper to make things worse) the more you are putting sideways stress onto the chassis spigot, which is probably why you see so many chassis with it snapped off. I did think of helicoilling mine so at least there is a decent thread to screw into but there is not enough metal to take the helicoil. I assume it is an old design, long before the current regime, it just intrigues me as to why?

[96RAF]

Item 20 looks as if it has other duties than holding the front of the motor down and Item 9 upright plate looks as if it takes all the load pushing it into the cast base unit. Any distortion of the Mazak parts will lead to misalignment.

[atom3624]

I think 20 is an additional weight, front motor locator, and was used for DCC / blanking plug mounting?

No wish to pull any of my 3 apart to confirm!

Al.

[ColinB]

No atom3624 leave well alone. I have a brand new one I bought cheap and I no intention of taking it apart, for one, the fit between body and chassis is incredibly tight. The one I had all the issues with was a non runner mainly due to Mazak rot. I have enough spare pieces to build a chassis, I will see if I can do that and then you can see what I am getting at. Either way it doesn't matter much, unless Hornby do a retool on it, it just intrigued me. On the one I modified I opened up the spigot hole and filed the motor end mounting down so that it fits parallel with the chassis, meaning that there is only upwards stress on the spigot.

[ColinB]

Well I eventually got to the bottom of the issue. On the new part that clamps onto the spigot, Hornby undercut the hole so that the hole at the top is larger than the one that attaches to the spigot. They had not undercut it deep enough so the mount doesn't go fully home, so the clamp is not tight. I just drilled the hole to be the same diameter all the way through and used a screw and large washer at the top, rather than just a screw as Hornby did. I assume on the production ones they get it right.

[Ruffnut Thorston]

Hornby Service Sheet HSS 305C from 2008.