DETAILED REVIEW RETROL Model Beam Steam Engine Kit and Horizontal Boiler with Flyball Regulator - EngineDIY & Chiltern Model Steam Engines

DETAILED REVIEW RETROL Model Beam Steam Engine Kit and Horizontal Boiler with Flyball Regulator - EngineDIY & Chiltern Model Steam Engines

Review Summary

 The Retrol Beam Engine and Boiler kit is fully machined and can be assembled easily into a working model steam plant with simple tools (provided). It is not actually a kit of individual parts more a number of subassemblies of parts. This reduces the potential pleasure of building the steam plant but may help a complete novice to model engineering.

 On opening the box the initial view is that this is a small but quality beam engine and boiler kit, well presented especially for the low price (at time of writing around £250 depending on shipping options). It does however have areas of poor design and some in its manufacture which will reducethe pleasure of ownership. The burner in particular would stop me from recommending its purchase for a child or complete novice.

 An experienced model engineer could correct or find workarounds but most experienced model engineers would want something more of a challenge, look more authentic, have fewer compromises to cost and have the ability to create something unique to themselves.

 In operation under steam the engine and boiler runs well with some limitations mainly due to the burner.


 EngineDIY ( is a Chinese WEB site that acts as an online retailer for several brands of Chinese model engine manufacturers, such as Musa and Retrol – I have bought many of these products in the last couple of years some excellent, many needing rectification because not enough time has been spent on the final prototype before going into full production.

 EngineDIY approached me in May 2024 to give an honest review of one of their recent products, the Beam Engine and Boiler model steam plant kit.

 It is possible Retrol/EngineDIY will take note and rectify the points I have found but best to assume it is likely they have already made a large batch and so an improved version will be some time in the
future, if ever.


 It is clear Retrol have invested in excellent packaging and glossy documentation sheets, great to show to customers in a shop environment. Included are all the bits and pieces, tools, etc., needed to build and operate the engine, apart of course from the fuel.

General Assembly

 Reviewing the assembly sheets there is a diagram mentioning some safety aspects, but there needs to be more guidance about safety and not leaving young children unsupervised, dangerous flames,
safe handling of fuel, carbon monoxide risk, etc.

 The step by step assembly instructions are drawings rather than actual photos which are good but lack often needed supplementary information. There is a numbered parts diagram but no part names, which is important from a learning perspective; for example rather than just “part 3” include a table that names this as the Connecting Shaft, likewise “part 7” is the Cylinder and Chest Subassembly.

Step by Step Assembly Observations

Available is a YouTube video of the engine assembly steps, see;, but not the boiler.

Taking each of the assembly sheet steps in turn, these are my observations;

 1. I cannot see how the Cylinder and Chest (part7) are fixed together. There are no screws or signs of solder. I would be concerned how long the parts would stay together if they were just glued. It should be pointed out the retaining screws should be left slightly loose at this

 2. I like how the retaining screws for the parts in step 1 are accessible through holes in the mounting plate – needed for fine adjustment later. It should be pointed out the nuts/screws securing the Main Bearing Pedestals (parts 11) should be left slightly loose at this stage.

 3. It is a shame the Beam, Watts Parallel Motion, Piston, Shaft, etc., (part 1) are provided as a completed subassembly. As assembling all these parts would have been very satisfying.
Disappointing that there is no Piston Ring – hard nylon would not drag much but dramatically reduce steam leakage.

 4. The Roller Bearings (part 18) are too loose, they should be a press fit in the Main Bearing Pedestals.

 5. As earlier, it is a shame the Eccentric Rod, Crank, Valve, etc., (part 12) are provided as a subassembly and not separate parts. As an important education point, the Eccentric/Valve controls the flow of the steam into the Cylinder which is key to a steam engine’s operation.

 6. Good that the grub screw is preinstalled into the Flywheel hub (part 4) as it is difficult to do when assembling on the Shaft. The Flywheel is made out of Aluminium; a bigger and/or steel Flywheel being heavier would allow the engine to run slower, which for a Beam engine is more visually appealing. There is a noticeable wobble on the Flywheel which I know many people will not accept.

 7. The screws for the Bearing Pedestals (part 11) need to be tightened up gradually while rotating the Flywheel ensuring very smooth rotation. Also the Eccentric Wheel (part 12), Spacer (part 15) and Pulley Wheel (part 16) should be pushed up to the Main Bearings to hold them in place. The Spacer’s internal bore is drilled out slightly too large so appears to wobble on the Crank Shaft (part 14).

 8. The diagram does say to screw the Crankpin (part 10) anticlockwise as it has a left hand thread, which is fine but it would have been easy to design the engine run in the opposite direction hence a normal thread could be used. The rest of the screws should be tightened up gradually while rotating the Flywheel ensuring there is no binding – generally all the moving parts have a loose fit so it should be easy with care to get very free movement. Any tightness will consume steam pressure.

 9. Similar to earlier comment, it would have been nice to build the Fly-ball governor/regulator (part 17) from separate parts rather than just a bolt on a subassembly. The bearings holding the Regulator’s shaft are very loose but there does not seem to be a way of easily tightening them up by pushing them together as it looks like the components are glued. I don’t like the silicon tubes (parts 35) but they allow the price to be kept low – the design should at least be adjusted so that the brass tubes align accurately (they are around 1mm out). The longer of the screws (part 23) should be tightened gradually ensuring the regulator valve can move freely up and down.

 10. Before continuing the assembly I tested the boiler using air pressure. The safety pressure valve released at around 20 psi which is fine being the highest pressure I would risk in this setup and the boiler held most of that pressure for a couple of minutes, so no serious leaks.

 11. The Boiler support/mount (parts 29 – 33) went together nicely.

 12. The Boiler slotted into place easily in its mount.

 13. As did the Boiler Bands (part 32), again keep the screws loose until they are all in place and then tighten.

 14. The brass pipe coming out of the regulator for connecting to the boiler is far too short. I would recommend that the brass pipes from the regulator to the boiler should be long enough, aligned and bent such that they are close together so that the silicon connecting tube is only bridging a short distance and is kept straight. This would be more secure, look better and would not cost much more to make.

 15. The Burner (parts 36, 37, 38) is just an easy push together, however….

 16. The instructions say the Burner uses 95% alcohol as fuel. In the 1960s and 70s Mamod steam engines, amongst others, ran on methylated spirits (denatured alcohol is the same as methylated spirits aka meths). For safety reasons this was superseded by solid fuel tablets and more recently by fuel gel when the fuel tablets were regulated in the United Kingdom.
So the Burner should be redesigned to use fuel gel, see Forest Classics for fuel gel As a priority I would recommend replacing the alcohol/meths burner provided with an open pan fuel gel burner which would be safer to use and cheaper to manufacture.
 As mentioned earlier there needs to be more guidance about safety and not leaving young children unsupervised, avoiding burns from flames, how to handle fuel, carbon monoxide risk, etc., etc. – as this is not obvious to a novice.
The tank/tray (part 27) to catch the condensed steam from the engine is a nice idea, unfortunately it is too high to just slide under the base, a simple design change.

Operating the Engine

 The following observations were made when running the engine and boiler, see also my accompanying video;

 1. The engine should be operated in a very well ventilated area, preferably outside. Emphasising my earlier comments on the burner, it is very easy to spill the meths when filling the burner which is a safety concern and meths is not a pleasant smell.

 2. To reduce the time to get the boiler up to steam hot water can be put in the boiler. Filling the boiler is by unscrewing the pressure relief valve – a syringe or similar will be needed as the fill hole is too small for a funnel, also open the steam outlet valve on top of the boiler.

 3. Using the sight glass on the end of the boiler, fill to approximately three quarters, that leaves space for the steam to be produced.

 4. Wear flame retardant gloves to light the burner as spilled meths may also get ignited – it can be a little difficult to see in bright light but it seemed easy to light both wire wicks (part 38). Push the lit burner under the boiler.

 5. Make sure the steam outlet valve is closed. Depending on the initial water and ambient air temperature, the pressure valve should start to release in 5-10 minutes, hence indicating steam is being generated.

 6. Open the steam outlet valve and if the engine does not start, rotating the flywheel should get it going and clear out any water/condensed steam.

 7. The engine ran well straight away, steam/water does leak from the fly-ball governor valve but not enough to cause a problem and surprisingly very little from the piston despite no piston ring. As mentioned earlier any binding will consume steam pressure but if the engine is assembled properly it should need little pressure to run unloaded.

 8. Testing by manually operating the fly-ball governor (first removing its pulley belt) the governor does cut off steam to the engine when the fly-balls are moved outward. I think some adjustment may be needed to get the engine to run slowly controlled by the governor but I did not have time to further test. Overall however the governor is good visually even if the speed can be controlled quite well by the steam outlet valve.

 9. The burner output is not sufficient to keep the engine running very quickly for more than a couple of minutes before the steam outlet valve has to be turned off and steam pressure allowed to rebuild. The meths in the burner will last around 10 minutes.

 10. The whistle works okay but its steel operating lever gets very hot and drains steam out of the boiler very quickly, so best not to use it – Retrol should either make a much smaller version with a plastic lever or just save the cost and not include at all.

Review by Simon at Chiltern Model Steam, June 2024

Useful links;

EngineDIY product page;

Video of engine assembly;

Other video of engine in steam;

Other video of engine in steam;

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