Mountain wrote: The GWR 101 was an economical and more practical compromise having simplified rods, larger wheels for better current collection and shared the motor, conrods and wheelbase with the last of the Triang 0-4-0's.
No 101 continued Hornby's practice of basing it's little 0-4-0 on a protoype. Nellie could be traced back to an LSWR C14, but grew a little to fit it all in. No 101 matches up quite well to the only photo and drawing I've ever seen of her. It was built as a test bed for Holden's oil firing system, which like many GWR trials was never allowed to run for long, then converted to a coke burner, working first on the Wrington Vale branch, then as a yard shunter at Swindon until the one off boiler was due for replacement, at which point it was scrapped.
I'm not sure which came next, but the chassis, minus the conrods and cylinders was used for an 0-4-0 diesel, and the full chassis was used for the CR Pug/Smokey Joe, which was produced with a diecast footplate to give it a little more weight. but again the dimensions were allowed to expand, the wheelbase was about a foot too long, so an extra foot was introduced into the saddle tank, behind the dome I think. The section of firebox between the tank and the cab front was raised to clear the back end of the motor.
The same chassis has also been used in an cut price 0-4-0 Thomas, and as Percy. They then had second thoughts and no more 0-4-0 Thomas models appeared but the body was used without a face as a freelance side tank. The early versions are renown as pocket rockets, some being very difficult to run slowly. At one time Dad-1 and I each had one example that would crawl along when needed to and so we were unlikely to see another smooth running one for years, however recent China made examples do seem to be more tameable. Worth knowing if you have a favourite one but wish it was less frisky, a quick chassis swap may be all that's needed.
