• Dismantle an Engine

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    The page provides information on how to disassemble your R/C Model Boat engine. Eventually, you will need to disassemble your engine. For changing piston rings, to wipe off water ingested on a flip-over or for any other reason, the day will eventually come.

    It's not a very complicated task, it only requires caution and the right tools. And that's the problem. Besides general tools you will need two special tools not readily available on hardware shops.

    Fortunately, none of those tools is too sophisticate and you may be able to manufacture then at your home shop easily. Below, you will find a explanation on how to:

    Removing the flywheel (rotor)

    To disassemble the engine, you must take the flywheel off. It is "well" fixed to the engine shaft by means of a nut, by the conical shape of the shaft, that locks it against the also conical hole of the rotor and by the key that runs into the shaft slot. Bellow, a picture of a stock Zenoah flywheel already disassembled from the engine.



    Shaft nut

    • The first step is to take off the nut that holds the rotor to the shaft. To do this, you must lock the piston, to prevent the engine from turning with the nut. Putting levers or screw drivers between the rotor and the crankcase may damage the rotor and/or the case.
    • The correct way to do this is locking the piston with a tool - a stopper - that you can manufacture as follows:
    • use a spark plug the same thread as the engine's;
    • break and take off the spark plug isolator. To do this you will need to use a grind-stone or a lathe to cut off the steel ring that fixes the isolator to the metal body of the spark plug. With time and patience a Dremel will do the trick.


    • put a 6 mm Allen screw into the spark plug, with the head at the bottom of it;
    • on the other tip screw a 6 mm nut. Your tool is ready.


    • To use it, screw it into the spark plug hole and turn the rotor by hand until the piston touches the tool.
    • From that point, you can take off the nut that holds the rotor without damage to any part of the engine.


    Taking off the flywheel

    • Just taking off the nut doesn't free the rotor. Remember: the engine shaft is conical, as the center hole of the rotor. They were tightened against each other at the time of the original assembling of the engine and to separate them you will need another special tool, that, as well, can be made with minimum resources and a little skill. Introducing levers or screw drivers between the flywheel and the case and hitting the shaft with a hammer will certainly damage your engine.

    Follow these steps to make the right tool:

    • use a aluminum bar with those dimensions:
    • length: 4 inches (100 mm)
    • width: 1 inch (25 mm)
    • thickness: 1/2 inch (13 mm)


      Note: those dimensions are just indicatives and are not critical. Use the material available, just take care not to use a very thin one, to avoid the tool bending when in use.
    • mark the center of the bar;
    • carefully, measure the distance between the center of the engine shaft and rotor's threaded holes;


      A: central hole B: left threaded hole C: right threaded hole
    • transfer those figures to the aluminum bar, from the central mark done in (c)
    • drill the central mark with a 6,5 mm drill;
    • make a 8 mm thread on the 6,5 mm hole;
    • check the diameter of the rotor's threaded holes (6 mm on Zenoah engines)
    • drill the marks made in (d) with a drill slightly bigger than the diameter of the threaded holes of the flywheel. On Zenoah's engine use a 6.5 or 7 mm drill.
    • You tool is done.




    To use it, screw a 8 mm bolt on the central hole and put two 6 mm bolts across the other two holes. Screw the 6 mm bolts to the rotor, until the 8 mm central bolt touches the engine shaft.



    Screw the 8 mm bolt against the engine shaft until a crack is heard. Done. The flywheel is loose. Disassemble the tool from the rotor, unscrew the stopper from the spark plug hole and take the rotor off, taking care not to lose the little key that runs in a slot on the engine shaft. Continue disassembling as per manufactures instructions.

    Carlos Andrade