MAAA Wingspan

27 In some engines, there is a tiny roll pin inserted in the top of this crankcase that aligns the cylinder liner, preventing improper insertion. If it doesn’t have an alignment pin, remember how the ports line up with the crankcase or take a photo with the ‘smart phone’. Now ease the connecting rod off the crankpin and remove the piston and rod assembly. You have to be extra careful not to damage the piston ring (if present) during removal, I had this trouble the first few times. On some engines (usually modern four-strokes) the rod cannot be taken off without first removing the wristpin and piston. These engines will have an access hole in the rear of the case through which the pin is slid out, again just take your time. The O.S. .46 SF does not have this feature. Ok so, the crankshaft can now be eased out of the case and bearings. Remember to place the parts so you know when they came from for your first time. If the engine is bushed, the crankshaft should easily slide out. A light tap with a plastic or brass-headed hammer can tap out the crankshaft. Do not use a steel hammer or you will damage the threads and possibly ruin the crankshaft. Now that the engine is all apart, we can take the old bearings out and see how they are. Most of the time the aluminium case will have to be expanded with heat to release the bearings. I usemy covering heat gun to apply heat to help. You can easily distort the case with toomuch heat or uneven heating. Once the case is hot enough, a sharp tap on a wooden block should allow the old bearings to fall out. CLEANING Now for cleaning, I like to use a water-based citrus degreaser and an alkaline detergent when cleaning engine parts. Pour some citrus cleaner into a plastic container and use a toothbrush and small stainless- steel wire brush to clean the parts one at a time. I only use the wire brush for external surfaces, and the toothbrush to clean all internal parts. The nylon bristles won’t hurt anything but are stiff enough to clean each part well. Now I dilute some of the detergent 50/50 with water and wash the part again, before rinsing the part in clean warm water. After rinsing, set the part aside on a clean towel or even paper towel to dry. Spray a light coating of WD-40 as a rust preventative on any steel parts such as the crankshaft and fasteners after the rinse. If you reassemble the engine soon after cleaning, the assembly oil will also take care of that issue. I imagine that given we are all in lock down at themoment though, reassembly will occur straight away. For the external parts, some stubborn burnt-on oil can usually be removed with the stainless brush. I also lightly scrape off the heavy stuff with a Stanley knife. Heavy carbon that’s built up on the piston top can also be removed with a knife blade but be very careful not to nick the edges of the piston. Sometimes a small piece of a medium-grit 3M Scotch-Brite pad can also be used to clean the stubborn stuff or to at least get it to start moving. Some engines may need to undergo amuchmore extensive cleaning, but for themajority of engines a simple hand cleaning like I amdoing here is more than satisfactory. Once all of the individual parts are clean and dry, we can move on to putting this engine back together. INSPECTION Look over all the parts for wear and damage while the engine is apart. Inspect the piston and liner for scratches. The connecting rod should not have excessive play at either end. Inspect the crankpin for any roughness or wear. If an engine has been run with adequate lubrication and not excessively lean themating parts should be shiny and smooth. Parts that look scratchy and worn are usually signs that either foreignmaterial has passed through the engine, or it has been running without adequate lubrication. The bearings can be cleaned, slightly lubricated with light oil, and checked for smoothness and play. Any roughness will degrade the engines performance and a new set of bearings should be installed. It is also important to inspect the crankcase and crankshaft where the rotary valve is located. Even on a bearing engine, the fit of the crank to casemust be very close to provide a good, leak-free seal for the rotary valve, and to prevent excessive loss of case pressure out the front bearing. If you have an engine with a lot of wear and scoring in this area, it may be the end of MAAALogo. MAY WING SPAN