Fuel and Lubricants


Nitro Engine Basics
Nitro engines run on a highly combustible mixture of methanol, nitro methane (CH3NO2) and castor or synthetic oil.  Rather than using spark plugs, such as in typical 4-cycle engines, these engines use a method of combustion similar to diesel engines (granted diesels are generally 4-stroke).

Using electrical current and a glow plug, a hot spot is created in the combustion chamber.  This, in addition to the compression of the moving piston, creates the combustion cycle.  Within seconds, the combustion chamber and glow plug become extremely hot and maintain subsequent combustion without the need for the electrical "jump start".   This is what is often referred to as "dieseling".  The only thing that breaks this cycle is either lack of oxygen or fuel (or an un-timely death of the engine).

Nitro-Methane Content
Fuels are rated by their nitro-methane content, typically 10-40%.  The higher the nitro-methane, the more power to the engine.  Typically in 1/10 scale cars (with .12 engines), 10-20% is plenty sufficient.  More than that on these smaller scale cars will go wasted, since the engines to not efficiently convert use the extra-potent fuel and the hookup (traction) is usually marginal, at best.  They heavier 1/8 scale and larger cars can see significant increases in usable power by using these higher (30% and higher) nitro-methane ratings

In-Fuel Lubricants
These engines do not use any auxiliary method of lubrication.   Instead, they use the same method of lubrication found in most other 2-cycle engines.  Because of the physics of 2-cycle engines, the fuel passes both sides of the piston, including the crankcase.  This allows a convenient method of lubrication.  By actually combining the lubricants with the fuel, you can continually coat all the moving parts of the engine as the fuel makes its way to the combustion chamber.   Whatever lubricants are not absorbed by the metal they come in contact with are either burned in the combustion chamber or are discharged through the exhaust port.   This is why you will often see these broken down oils seeping from the mufflers or tuned pipes.   It is just the normal process of cycling through the lubricants. 

Most nitro-engine manufacturers recommend using a special "break-in" fuel which contain a higher percentage of lubricants for the first few dozen tanks or so.  This is to insure that the engine has plenty of lubrication in order to properly break in and maintain a good seal in the combustion chamber. 

This is also why we encourage users to tune their engines slightly rich (see Engine Tuning & Maintenance) so that there is a sufficient supply of these lubricants to  the engine.  Although running your engine lean may increase performance (temporarily anyways), it will be short lived if the engine doesn't have enough lubricant to maintain proper engine temperatures.

After-Run Lubricants
An important and often, overlooked procedure in maintaining your engine is after-run lubrication.  The benefits from this are two-fold.  First, as the engine cools after being run, moisture can build up inside the engine, causing corrosion.  The next time it is run, the engine will typically see some undue wear from the corrosion buildup.  Secondly, the lubrication process often enhances the starting ability by providing a better piston to cylinder seal.  Until the engine has had a chance to warm up, this seal is often sloppy, and just like the engine in your real car, a majority of the engine wear happens in the first few seconds before the lubricants in the fuel get a chance to recoat the engine's working parts.   You can find these "after-run" lubricants in your hobby store.  Usually a few drops down the glow-plug hole or in the carburetor right after you have run your car can significantly add life to your engine.

I cannot stress enough how important this is.  Just like running your engine rich is important for your engine's life, so is this simple process.   Don't let this one go unchecked.




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This page last modified: 07/26/11