Time for a Rebuild?Edit
Determining if your engine is worn out can be quite difficult, especially if you are new to the hobby. Common symptoms are that the engine will start and run for a bit, and stall, refusing to restart until the engine is cold again. This is because of the tapered design of the ABC sleeve in most engines. It will get enough compression to run when cold, but when it warms up and expands, the piston can't seal properly with the sleeve. The engine may also get impossible to tune, constantly overheating even when rich. This can all be frustrating and confusing to people who are new to the hobby.
While these symptoms are a good sign the engine is worn out, there are other causes of these problems, including air leaks and bad head gaskets. If you have a local hobby shop, you can probably take the engine there and have them do a compression test. Or you can buy a compression gauge and do it yourself. If the compression is low, or a compression gauge is not available, the only way to continue is to tear the engine down, and examine the parts for wear. There are only 3 moving parts in the engine, other then the bearings. At this point, you should read Rebuilding a nitro engine
A nitro engine requires the sleeve to 'pinch' the piston to maintain proper compression during operation. One can test an engine's pinch by removing the glow plug and rotating the flywheel while watching the pistons movement. As the piston comes to TDC (top dead center) the sleeve should 'pinch' the piston head, causing some resistance, if you can't feel any it is time to get re-pinched or replace sleeve/pisto
Glow Plugs Edit
A very easy to diagnose problem that will effect any nitro engine in its lifetime. Make sure that your glow plug coils glow bright orange almost instantly. The entire coil must light up.
Correct Pres Edit
The heatsink must be bolted/screwed onto the cylinder block in the correct manner and to the correct torque. Tighten fasteners opposite to one another first lightly and then tight. If you tighten them fully one by one you will not get a proper seal between heatsink and engine. There is a gasket in between the engine block and the heat sink.
Engine performance will suffer with any leaks, things to look out for are damaged o-rings and gaskets.
Engine troubles could be as simple as bad tuning. A good rule of thumb is that the factory settings on any engine will at least be startable. Check the nitro tuning page for more info.
Fuel Tubing Edit
Even a tiny leak in a fuel tube can cause an engine to lose tune and run erratically, when in doubt replace the fuel tube as it is inexpensive.
Old Fuel Edit
Nitro fuel captures water from the air and therefore goes bad very quickly. (think 5/7 months )