Quicklinks – OverviewPart 1 Part 2Part 3Part 4
01 Sentinel Project 2013



This project basically started off back in mid 2012 having made enquiries about some engines which looked interesting as my next and final project.

One of these was another of the Sri Lankan engines of a bo-bo design which I had seen during my trip to Sri Lanka. G2 type engines number 535 was at Galle in May 2006.

Another was of the shunters used at Ratmalana engine sheds during my visit in May 2006. Then Nigel Cox came up with his library of Sentinels information which he kindly loaned to me for a few months.

Thus came to pass the decision to design and build a Sentinel shunter of the Thomas Hill variety build. In all, a total of 292 diesel locomotives were built in the twelve years up to 1971. In 1961 a range of 0-4-0, 0-6-0, and 0-8-0 locomotives was added. All were powered by the 325 bhp Rolls Royce C8 SFL, 16.2-litre, supercharged diesel engines and known as the SR type.

During my visits to the model engineering shows I had noticed a chassis kit which might be suitable as a donor starter pack for my project


added [ 1170 mm long ] added

total new length 110 + 1170 + 110 = 1390mm long.

Use of 100mm x 50mm “U” channels added to each end enhanced the chassis length to an acceptable engine length of model. Plus another new buffer beam of 10mm thickness was added at each end.

actual engine length was 6480mm, divided by 1390 = 4.66 factor

but this gave the steps width as 815 / 4.66 = 175mm

the depth of the steps is about 340mm deep / 4.66 = 73mm

the Buffer beam width was 2590mm / 4.66 = 556mm, this chassis is actually 550mm wide, so conforms to requirements.

This wheel base was 1676mm / 4.66 = 360mm, this chassis is actually 500mm wheel base, but was considered to be acceptable.

So began my Sentinel project

A visit was arranged to the Nene Valley Railway, where I was once a member some years previous. Alan Wheeler, Dave Hartley and John Whitby were all very helpful and with the owners permission I and Clive were able to visit the railway and climb all over Barabel and take measurements to enable my Sentinel project.

These basic measurements were put into a data base and using the 4.66 factor to deliver a set of measurements that equated to my 7¼ inch scale engine sizes. I also used my own judgement to adjust sizes where necessary to arrive at a reasonable set of build sizes.

Now I was able to forward this project into an engine of the Sentinel type.

This new engine was a departure from all my previous locomotives in that this was inspired by Barabel (NVR) and Skippy (BRPS) and would be my first petrol/hydraulic powered locomotive fitted with vacuum pump and controls.

The main chassis kit was obtained from the EE at the beginning of 2013 and has since been transformed into a heavy haul loco of 550mm width x 610m high x 1500mm length, weighing about 315 kg. The body work design has been drawn from my NVR visit earlier this year, however as usual my own preferences of detail has been incorporated in this striking model of that engine type. It is powered by an electric start 196cc petrol engine coupled to an Eaton 7 transmission using heavy duty chain drive.

Once I had the basic engine chassis I now needed something substantial enough to carry the weight of the finished engine. I obtained a garden cart cheaply and then made up a new heavy duty frame which incorporated the cart bits, the rest being discarded into the scrap metal bin.

My custom built trailer only needed a small modification made to the canopy in order to take this new engine plus some more holding down eyes and turnbuckles to keep it secured when being transported.

The body work was laser cut for me by my good friends at Dale Fabrications using my own sketches. It is not a scaled model of a particular engine so any rivet counters could pick out deviations from the range of engines that were produced.

The initial track test debut took place on the 13th of August 2013, since when works are in progress to complete the safety systems before it goes into operational service. Once final testing has taken place and results are satisfactory the engine will be commissioned and put into service.

Another new design feature for this engine is that it will also incorporate a guards alarm control that can be activated by the duty guard to alert and warn the driver for safe operating.

Four bits of mild steel “U” channel were obtained from a steel stockists at Grantham, being cut to order to the required size, these were then offered up to the chassis and marked out for drilling and fixing to the chassis plus the new extra buffer beams had to be fitted. The spare new buffer beams had been ordered with the engine chassis kit and only needed cleaning up drilling and fitting. This completed stage 1 of the works.

A battery platform was needed to be fitted within the front of the chassis in the middle section that would hold a heavy duty Optima yellow top 12 volt battery suitable for powering both starting and operating of the electronics and control systems. This has been fitted so that it does not obstruct the air flow of the engine cooling 2 speed fan.

Inside the cab is a 100amp double pole isolator plus a fuse block for the aux. power services. (these have separate fuses fitted).

  • Engine Start.
  • Horns.
  • Lights.
  • Cooling fan.

On the other inside of the cab is a lever that activates the Eaton 7 transmission units hyd. dump valve to allow the engine to be moved “out of drive” to be pushed as circumstances demand when loading and un-loading. Chris Dixon CMD Engineering has kindly provided me with a “Dump Valve Lever kit” to experiment with which is fitted to my engine and with some modification is working satisfactory.

This engine also has a control lever of the “normal reverser type with notches” for the hyd. drive selector to engage forward or reverse. Thus ensuring a mid gear “NULL” point is engaged.

On moving pulling back the hyd. drive selector to the mid point NULL position it also brakes the engine so this needs careful handling when moving this lever during operation.

Unless a person is familiar with driving this type of engine drive system some serious supervised driving time is essential before allowing a person to drive with passengers or drive during a public running session.

The engine has an OFF valve in the fuel line.

The engine has a choke control lever which is only needed when starting for a couple of seconds from cold. The throttle lever being set to about 30% for starting. When the engine is warm the low revs should show about 1500, on moving off this needs increasing to about 2000 to 2200. Full throttle is around 3200 rpm.

The engine is fitted with a Gresley type drop arm for main throttle control / speed. Max rpm is obtained when in its fully back position.

The key switch has an OFF (shut down), IGNITION ON (running) and ENGINE START position (sprung return).

The engine has a vacuum pump which is powered from the main drive system whenever the engine is running. The vacuum control valve is fitted on the left of the controls desk together with gauges to indicate operating vac. pressures.

Main reservoir and train pipe.

Pressure setting valve is set at 20 ” vacuum, however this is adjustable from 15 to 21 inches vac.

The engine exhaust box has been taken off the top of the engine flange and a pipe made to extend the exhaust down to below the footplate, this then has a jointed box that fits onto the silencer making the silencer hidden under the rear left skirt. This protects the operator and the public from direct contact with hot pipes or surfaces. This pipe also has a heat shield tape applied to offer further protection in the rear of the cab, whenever the roof is removed.

The engine is a single cyclinder OHV air cooled 4 stroke 196cc dual start unit.

The expected design speed at full throttle and in max. forward drive is about 6 to 7 mph.

Chassis W1905 (Jan/2013) Villiers 196cc gasoline engine rated at 6.5 hp.

R200 – A1208004852 – *97/68 SA*2002/88*0112*400

Starter motor; Z.2001.1.0 (12v) BH120614.

The petrol tank is mounted in the front of the cab, replenishment must only be carried out in an area where the public do not have access. The tank capacity is 3.61 litres. Fuel consumption should not normally exceed 1.22 litres per hour during operation. After 2 hours running the engine should be taken into loco in order to top up with fuel.

Engine oil, takes 0.6 litres of SAE 10W-30

So what controls and instruments are fitted ?

A speedometer which can show multiple data as coded out at the time.

A rev. counter showing engine rpm.

A thermostat to show cab / engine room temperature (the two speed fan can then be operated at slow or fast as desired to keep the Eaton Hyd. unit cool.

The vac brakes control valve is on the left side on the controls desk to activate the vac brakes when fitted to the passenger stock.

A set up pressure of 15 in wg is used on this engine.

Quicklinks – OverviewPart 1 Part 2Part 3Part 4