This engine was made for "The Chantry Challenge Cup" which is awarded for the Mamod based mobile steam engine which can pull the greatest weight over a certain distance within a time limit; held at the Steam Toy Lincs event. I was going to just call it the 4WD but the name Red Devil was proposed and so I've adopted it. An earlier version, Mk1, competed in the first of these events in 2014. This improved Mk2 competed, and came first, in 2015 and in 2016 (with minor modification).
The Red Devil is based on a Mamod TE1A traction engine, fitted with four wheel drive, gearing and extra ballast to provide the pulling power. The boiler and engine are the standard Mamod parts. I have provided for two burner options. The first option is a standard Mamod TE1 vapourising meths burner. The other option is a Bix butane ceramic burner. An extra heavy duty towing bracket has been bolted directly on the side plates so that the stress is not transmitted through ther burner mounting. There is also a towing bracket at the front which can be used for double heading (or pulling in reverse). There is no steering, both axles being fixed. This has simplified the 4WD implimentation.
The boiler is a standard Mamod TE1A boiler, 1 3/4" diameter x about 4 1/2" length internally (it looks longer on the outside). It has a standard Mamod 1/4" safety valve. The whistle and overflow plug holes have been blanked off. Steam is fed to the standard TE1A engine port face, which has the improved Mamod cylinder and piston. This is the same dimensions as the original; 5/16" bore x 3/4" stroke, but the piston has oil retention rings cut into it. The engine is reversible in the usual Mamod fashion. The piston is connected to the crankshaft and flywheel, which are the standard Mamod parts but with brass bearings to improve lubrication.
Instead of the original belt drive from the flywheel pulley, the crankshaft has been fitted with two modified Meccano pinions, which mesh with unmodified Meccano gear wheels, which provide two different selectable ratios for the first stage for optimisation on the day. The rest of the gearing is done using standard Meccano gears, fitted between Meccano plates bolted to the firebox sides. The front and rear axles are coupled by a miniature roller chain and sprockets.
The rear axle has been fitted with improved bearing surface in the form of a stainless steel tube passing all the way through the firebox. It is lubricated with graphite powder to withstand the high temperature in the firebox. The front axle is similar, but lubricated with grease, and is fixed to the smokebox with meccano parts. All four wheels are fixed to their axles with screws into tapped holes in the axles. The sprockets (and gears in the later, high torque, stages of the gear train) have flats filed onto the shafts to prevent slipping. The wheels have been fitted with rubber tires for improved grip. In order to stop oil and water being splashed onto the wheels from the cylinder, a large drip tray has been added just under the cylinder.
To improve traction, lead weights were fitted inside the rims of the road wheels and also, optionally, in a tray slung under the boiler. The weight inside the wheels adds weight on the wheel rims but not onto the axle bearings, thus reducing friction. The weights slung under the boiler are easily removable if they are not required.
At the STL 2015 event, the Red Devil pulled a total weight of 70 lb plus one house brick, on two trailors, up a slight incline. The main problem was wheel slippage.
For the 2016 event, I added even more weight to the wheels, using lead sheet disks fitted to the outside of the wheels. These are easily interchangeable so that the weight distribution can be changed. (The front wheels tend to lift off the ground if the weight is evenly split front-back). The bottom three photos on the left and the bottom video below show the modified wheels.
The engine has been painted in red and black (hence the name) but very little else has been done to improve the aesthetics!