Loyal Cycle Engine

A model engine by Mick Cherry. This engine has undergone some major design changes to get it running exactly right and so you will see some changes to the design as it progresses through the article.

I knew about the Loyal Cycle engine but had put it to the back of my mind. After my Flame Engine had got damaged I thought it a shame to not use the main casting for something, and that′s how it came about.

I started to search online and found this article by E T Westbury.

There were some diagrams but the best thing was a timing disc, and it was from this that I built the engine. It is dead simple, with the inlet valve being sucked open and the exhaust valve being blown open. Imagine the engine is already running, and it has just fired. The piston is on it′s way towards BDC, when it reaches the exhaust port the pressure blows open the exhaust valve and the first part of the exhaust cycle takes place. Once the pressure has dropped the spring will then close the valve. With the piston still travelling down we now get a vacuum, which in turn sucks open the inlet valve and draws in a fresh charge of fuel. The piston now passes BDC and starts going up to TDC. As the compression starts to build up the exhaust valve blows again clearing any further burnt gas out, and trapping the new charge in the combustion chamber. When the piston finally covers the exhaust port, it is now on it′s compression stroke, where it carries on to the point of ignition, and off it goes′ again.

So from that you can conclude that it is a 2 Stroke.

You must excuse the lash up for the cooling system, but the engine was running on the hot side, what you see is the end result, so the next move will be to make a proper job of it. With the engine getting nice and loose I took it round to mate Dick Barnes, you can see his Hot Air Engine on the site. I ran it up and got it nice and warm then Dick got the following readings using his rev counter, 100 rpm tick over and 900 rpm max.

When I first ran it I had the flywheel from the flame engine on but although the engine was very fast it was far to fierce, and it had to be calmed down. The combined weight of the two flywheels is 51/2 pounds, and it needed all of it. What I have now is a nice steady engine that thumps just how I like it.

The engine does not have piston rings, it has a cast iron lapped bore and piston, they never wear out.


A Major Update

I have finally got the Loyal to a standard that I am happy with. It was very vicious when I first built it, but have now calmed it down. It does not throttle all that well but runs nice at a constant speed, so that is how I have set it up.

The result is an engine that sounds glorious running, switch the speakers on and watch and listen to it run in the video below…

and now the engine modified and running really well:


About Nigel 192 Articles
Have been making models since I was around 7 years old and using a lathe from the age of 11, a self taught engineer with a passion for making model engines.

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