The RC nitro car engine
The rc nitro car engine has evolved over the years into a very robust and reliable little power unit, and modern nitro (also called 'glow plug') engines are much more reliable and powerful than they ever were.
They vary in size of course, but the most popular and widely used engines are the small-block ones. These generally range between the .10cu.in. and .17cu.in. capacity (cu.in. stands for cubic inch). It's common for nitro engines to be referred to by this size ie a '10' size engine or a '17' engine etc.
The engines can have different features such as rear or side mounted exhaust, barrel or sliding carburetor, pull start or non-pull start and can be modified by replacing certain parts to increase performance. But the average rc car or truck owner who isn't in to competition racing will almost certainly just keep their nitro engine exactly as it was when it came out the factory, as the performance of the engine will be more than adequate for the car or truck that it's in.
Browse a selection of rc nitro car engines.
Two fairly typical rc model car nitro engines are shown below; a pull start one (left) and non-pull start (right):
The basic parts of a nitro car engine
A model nitro engine consists of just the fundamental parts of any internal combustion engine.
The cylinder head sits on top of the crankcase and has cooling fins to greatly increase the surface area of the head, to catch more air for cooling.
Inside the cylinder head is the combustion chamber which is home to the piston. This is the part that moves up and down very quickly as the fuel and air mixture within the combustion chamber ignites.
The piston is connected to the crankshaft, which is a horizontal shaft running through the crankcase and is connected to the clutch of the car.
Sitting at the front of the engine on top of the crankshaft is the carburetor, which is the part of the engine that introduces the fuel into the crankcase. The fuel / air mixture inside the combustion chamber is ignited by a glow plug, screwed into the top of the cylinder head.
The basic parts visible from the outside are shown in the diagram below:
How a nitro engine operates
RC car nitro engines are 2 stroke whereas most larger internal combustion engines are almost always four stroke - with the exception of things like small lawn mowers or scooter engines. Being 2 stroke means that it really is a very straightforward thing, with not too much that can go wrong.
2 stroke means that the piston just needs to complete one down-stroke and one up-stroke within the combustion chamber to complete the process of drawing the fuel and air in, converting the ignited mixture into raw power and then expelling the exhaust gases. A 4 stroke engine needs two complete revolutions to do the same.
The piston will keep on moving up and down (hopefully!) so long as the fuel/air mixture is being ignited, but how does the whole process start?
Well, the fuel/air mixture needs to be introduced into the crankcase at the bottom of the combustion chamber before anything can happen. This is done by 'priming' the engine, which either means holding a finger over the carburetor venturi or exhaust opening while slowly turning over the engine by hand, or just squirting fuel directly into the carburetor from a plastic bottle with a fine nozzle. Either action makes sure that fuel enters the crankcase.
Now that fuel is in the crankcase and has mixed with air, the glow plug needs to heat up and the piston needs to move up and down. So to start, the nitro engine needs to be turned over manually which is either done with the pull cord, if it is a pull start engine, or by an electrical engine starter.
At the same time, the plug is made to glow red hot by connecting a glow plug igniter to it for a few seconds; the filament of the plug heats up immediately.
With the fuel/air mixture sitting in the crankcase, it needs to be moved up to the top of the combustion chamber and ignited in order for the engine to start running under its own power. The mixture is forced to the top of the chamber during the piston down-stroke; as the piston moves downwards, so it pressurizes the area of the crankcase where the fuel/air mix is and forces it up small ports, or channels, that run up to the top of the chamber. The mixture is then ignited by the red hot filament of the glow plug.
Unless the engine is in poor condition or badly tuned, it should fire up after just a few seconds of being turned over.
When the piston is at the point just before the mixture ignites, it is covering the exhaust ports which run from the sides of the combustion chamber through to the muffler. When the fuel/air mixture does ignite, the resulting explosion forces the piston back down, and on its way down the exhaust ports are uncovered and the burnt gas mixture leaves the chamber via the ports.
The momentum of the spinning crankshaft makes the piston move upwards again and the whole process starts over.
Although the glow plug was made to glow red hot initially by a battery, once the engine is running then the high temperature inside the combustion chamber keeps the plug glowing. If the plug fails, then the fuel/air mix will not get ignited and the engine will stop.
A failed glow plug is usually the biggest cause of nitro car engine starting trouble and you should always carry a selection with you. Glow plugs for rc cars and trucks carry different ratings, so check your engine requirements according to the manufacturer recommendations.
If you're looking to buy a nitro car engine, try here.
