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How To Rebuild Your RC Engine - Diagnosis and Teardown Part Two

Article by Kenny McCormick

We're now ready to remove the sleeve. Remove the head bolts you threaded back into the block and set them aside somewhere they won't roll away. Next, take note of any indexing marks present. My sleeve has a notch in it that points towards the exhaust port.

Yours will likely differ, but there WILL be something to align the sleeve with the ports. With that noted, slowly rotate the engine.

The piston should hit the pinch at the top of the cylinder, as mine did, and push the cylinder up a bit. If you're lucky you should be able to just grab the sleeve and carefully slide it out. If not, you will need to insert something into the port.

NEVER USE A METAL OBJECT FOR THIS! Use a plastic or wooden one instead, I like the end of an old mechanical pencil. With your non-metallic object in the port, turn the engine again. The engine should force the sleeve back up through the top of the block and out. Set the sleeve aside, it's now time to remove the piston.

If you use pliers for this make sure you put fuel line over the jaws. You do NOT want to nick this part.

With the sleeve out the piston should be loosely flopping around inside the block. The engine should be near TDC now, if not put it there. Then, stick your finger inside the back of the engine and carefully slide the rod up and off of the crank. If your engine is too small for this, you may use needle-nose pliers, forceps, or tweezers, but be 100% sure you put some fuel line over the jaws first. If you nick the rod you may weaken it to the point it breaks, and when the rod breaks it usually destroys the block as well. There's no rebuilding an engine that failed because of a snapped rod. The rod should smoothly slide off of the crankpin, once it does, turn the engine upside down with your hand over the top of the block and the piston will drop down into your palm. With the piston out you may re-install the head bolts, again only far enough to keep them from getting lost.

With the piston out you have good access to inspect it. Look for deep scratches like the ones above. The piston should be a bit dull on the sides, this is normal, the piston is softer and thus is designed to wear more than the sleeve. It should, however, be smooth and free of any scratches. Check the rod play as well, it shouldn't rock against the wrist pin, only sliding up and down the pin as well as side-to-side in the direction it's designed to. If there is play, replace both parts... rods and wristpins are cheap and you don't want either one letting go. If your engine failed due to age you should replace the rod anyway, as the bushings in it are designed to wear instead of the wristpin and crank and likely have done so.

The next step in the teardown is to pull the pin out and seperate the piston. On some engines it will slip right out, these engines have two teflon buttons that center the pin inside the cylinder while the engine is assembled. DO NOT LOSE THESE BUTTONS! You will need them. My engine uses small metal snap rings that retain the piston, and there's a bit of an interference fit as well. I highly suggest you buy spares of these even if you don't need them, as they tend to mistake themselves for a space shuttle when they start to come out. Removing them is pretty simple, a pair of forceps makes pretty short work of them and I usually work with the piston below a paper towel or washcloth to catch any skyward clips. You need only remove one clip.

Don't worry about scratching the pin bore, you won't be using this piston again. Just don't ruin the pin itself.

With one of the clips out, grab an allen key that is just slightly smaller than the pin bore. Grip it as shown in the above picture and squeeze. It should push the pin out. Mine was a bit tight, what I did was I grabbed a screwdriver and gave the allen key a few light whacks with the handle end. Knocked the pin right out, didn't damage anything.

The final step, and this is mostly just for inspection purposes, is to pull the crank. On some engines the drive washer pops right off; it's just a matter of lightly tapping the threaded end while the back of the engine rests on a pillow or something. Your hand will also work. My Super Tiger, however, has a pressed on drive washer. On this engine, heat the crankcase in the oven. 15 minutes at 250 degrees Fahrenheit oughtta do it. Grab it with pliers or oven mitts and give it the same whacks. The drive washer should pop right off and the crank slide out. It may take the rear bearing with it as well. Be careful not to lose the copper cone that goes between the drive washer and the crankshaft, without that cone it won't work come reassembly. Once you're done with either method set the block aside and inspect the crankshaft. The area where it rode in the bearings should be smooth and shiny, and the area around the induction port should be free of scratches. If there's really deep scoring here the engine likely sucked in a lot of dust and dirt, very small minor ones are pretty normal for high-mileage engines. The crank should also be free of rust, although some castor varnish on the end inside the crankcase is entirely normal.

Oh, and give those bearings a spin. They should feel buttery smooth. If they do not, replace them, they are cheap and when they fail they tend to take the rest of the engine with them.

With that, your engine is torn down! You're ready to put the new parts in and get it going. I cover that in the Engine Reassembly article that can be read here.

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