Engine Operation & Care
As with all things mechanical, an engine needs to be operated correctly and have regular maintenance to be at it’s best. Many an engine has been ruined by not observing basic rules.
It is a good practice to disassemble an engine to check for remnants of production ‘swarf’, dirt , flaky chrome plating etc before ever turning an engine over. It is very rare that an engine can be checked (no need to remove the ball races) and found to be perfectly clean.
Use very fine abrasive paper to imitate a needle file, to carefully remove any sharp edges in ports etc.
DISASSEMBLY ETC
Much of the following page or so assumes the user has the skills to dismantle an engine and reassemble it correctly. To do this is not hard provided several golden rules are followed.
Work on a clear and clean bench top, and use the correct tools to fit the bolts etc.
Always keep a record of how the engine comes apart, some components may need a fine scratch mark for identification, for example put a very fine X on the rear of the conrod before removing it.
Never force a component with a metal tool, for example never use a screwdriver in the exhaust port to lever out the liner.
To remove the crankshaft which uses a tapered collet to lock the prop driver (generally very difficult to disassemble), A) use a bearing puller to pull off the driver if it can be fitted (usually not), or B) placing the prop nut on the end of the thread and with the backplate off and conrod removed, use a wood block to cover the nut, and knock the assembly loose with a hammer.
Bearings should not come loose without the aid of heat. NEVER force the bearings out .... let them drop out with heat. Heat the crankcase (with all other parts removed) by placing it in an oven (try at 120 degrees C, and increase as necessary), or heat the area evenly with a portable gas torch. Often the rear bearing will drop out with a sharp knock on the bench. The front bearing will need to be pushed from behind with a suitably sized wooden dowel.
To install bearings, use the process in reverse. It is vital the bearings go back into the housings all the way, and square. It is often necessary to make special wooden or Teflon holders to aid the process. Take care to not force the inner race of the bearing when installing (or removing if the bearings are still in good condition).
The bearing holders etc, should be made to only push against the outer rim of the bearing, and to be an interference fit inside the bearing shaft hole, to hold the bearing onto the mandrel.
The process of removing and installing bearings with heat works on the principle of expansion rates, the aluminium crankcase expends at a greater rate than the steel bearings. On some occasions the liner may also need removing via this method.
RUNNING IN
The modern ABC or ABN engine generally does not require much running in, and can often be done in the aircraft in flight.
The first 5 minutes should be done with a small prop running very rich with intermittent faster periods. If it appears obvious there are no problems, go flying ... assuming the model will fly OK under powered.
It is vital that the next 30 or more minutes of operation be done without stress. The best procedure is to use a smaller than intended prop running richer than usual at about the same as the intended end use rpm. If after a time it is obvious the engine can maintain a correct tune without leaning out (a sign of excess heat due to being too tight), then bolt on the intended prop and go fly, still keeping it rich for a while.
OPERATION
The same rules for running in also apply to general operation. There are no prizes for running an engine too lean, except the hobby shop, who will sell you another engine sooner.
Always use fuel filters and maintain the fuel system in good order. It is a good idea to provide the tank with some sponge rubber insulation to prevent ‘frothing’.
Mount the engine securely, and only use balanced spinners and props.
GLOW-PLUGS
Glow plugs are a vital and commonly disregarded part of engine performance. More than half of the cost of a glo plug is the element. The fine wire elements are made from alloys combining platinum, iridium and rhodium in different proportions. Variations of the alloy, thickness of the wire, length of the wire and the volume of the plug cavity are adjusted to produce different plugs for different applications.
Use the correct plug, and change it if it looks a bit worse for wear. Use the warmest plug practical.
Plugs come in many different shapes and sixes. All common plugs use a 1/4 x 32 thread. It is handy to own a tap for this uncommon thread size. If you have any doubt about the quality of the thread in the head, a quick use of the tap can save a lot of trouble.The common variables in plugs are..
Heat range ‘Hot’ plugs for small / slow running, engines that do not develop much internal heat of their own, through to ‘cold’ plugs in hot running engines (i.e. racing engines). Using a ‘hot’ plug in a racing engine will cause pre ignition and quick destruction of the plug. Using a ‘cold’ plug in small engine will cause very unreliable running.
Reach Plugs come in short, long and medium reach. This refers to the depth of thread. The ideal depth of plug is one where the bottom of the plug is level or marginally short of reaching the combustion chamber (at the end of the threads in the head). It is often necessary to use extra plug gaskets to achieve this.
Voltage Plugs are sold in different voltage ranges, from 1.2v to 2v. Using a 2v battery on a 1.2v plug may ‘blow’ it, and using a 1.2v battery on a 2v plug may not heat the element sufficiently. Many ‘hard to start’ situations are caused by a weak starting battery.
Important Tips When starting an engine, leave the plug leads on until after the engine has been run up to full throttle for a few seconds. Take note of what happens to the engine RPM when the leads are removed (it is safest to do this at idle). If the engine picks up RPM (rare), the plug is too hot or the combustion ratio is too high. The reverse applies, if the engine drops a lot of RPM, the plug may be too cold or the compression ratio is too low. Please note that a small RPM drop is normal, especially at idle.
If the engine is ‘crunching plugs’ or sounding harsh or hot and bothered when it shouldn’t, add an extra head shim to decrease the compression ratio. This is most likely to happen when using large props, high nitro or a cowled engine.
If an engine which is normally very reliable, suddenly starts to ‘crunch’ plugs, it is often a sign of internal wear. Usually it is a bearing or conrod beginning to fail.
COOLING SYSTEMS
For cowled engines it is vital that cooling air be provided to the engine and exhaust system. It may even pay to up the oil content of the fuel.
The hot part of an engine is the exhaust. Rear exhaust engines require air to be ducted to the back of the cylinder. The hot spot for side exhaust engines is to the rear of the exhaust.
Remember the air outlet should be double the inlet area.
CARE
If flying on a dusty field, use a good air-filter.
Regular cleaning (externally and internally) is necessary for continued good performance. A build-up of carbon deposits will impair performance by making the engine run hotter. If the deposits on the head (internally) build up enough, the effects can be severe.
The outside of the engine should be kept clean. Eventually baked on fuel deposits will need to be removed, especially if not regularly cleaned. One product to use for this is an aluminium frypan cleaner, but take care to follow the instructions.
The head and exhaust port etc should be periodically cleaned. If done regularly they can be wiped clean. If the deposits have baked on hard the only alternative is to carefully scrape the areas clean.
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