Cleaning is a continuous process, carried on as the shrouding, fuel tank, muffler, flywheel, clutch, and other components are removed. Use a nontoxic degreaser and, if possible, perform initial cleaning outdoors. Home mechanics like to use Gunk aerosol, which is a strong alkaline that converts grease and oil to soap in the presence of water. [...]
Cast-iron was the wonder metal of the industrial age: inexpensive, easy to pour and machine, and unique in the way it could run against itself without protest. Iron cylinders and cast-iron rings are fully compatible. Classic engines, such as the Harley-Davidson Knucklehead and Volkswagen air-cooled fours had gray cast-iron cylinders that produce a dull thud [...]
Wipe the bore with a clean shop towel. Severe damage is obvious to the eye, although touch is a far better guide to surface finish. Fingertips can detect irregularities as small as 1 μm (1/25,000 of an inch), or about 100 times smaller than those we can see. Cylinder wear appears as: Discoloration that signals [...]
With good maintenance, a piston should outwear two sets of rings before replacement. Normal wear polishes the piston skirt to a uniform sheen without the deep scores, carbon streaks, or weld splotches caused by overheating or loss of lubrication. The piston in Fig. 6-14 exhibits this sort of damage, as opposed to normal wear. The [...]
Most manufacturers chamfer the lower portion of the cylinder barrel to compress the rings as the piston is inserted. Makers of engines with detachable barrels sometimes furnish their mechanics with a ring compressor, although this tool is more of a convenience than a necessity. Oil the piston and rings liberally with two-stroke lubricant and, if [...]
Note the orientation of the rings and any features that distinguish one ring from another. Two-stroke rings abut against anti-rotation pegs in the piston grooves. Newer engines often have offset pegs that eliminate confusion during installation (Fig. 6-8). Older engines had the top side of each ring marked for correct installation. The marks vary, but [...]
Access to the piston varies with engine design: Detachable cylinder barrels, like the one shown back in Fig. 6-4, lift off once the stud nuts are removed. If the barrel sticks, glancing upward blows with rubber hammer will break the gasket seal. Cover the crankcase cavity with a shop rag. It is also good practice [...]
Detachable cylinder heads secure with four cap screws or long studs that thread into the crankcase. Loosen in an X-pattern. Rusted threads can bind the nuts to their studs with the result that the studs unscrew from the crankcase. If this happens, unthread the nut while holding the stud in a softjawed vise. (A pipe [...]
Critical fasteners, such as those that hold the cylinder to the crankcase, should be secured with a few drops of medium-strength anaerobic adhesive, such as Loctite 242 (blue). Locktite 222MS (purple) is appropriate for 1/4-in. and smaller fasteners. These and equivalent “chemical lock washers” from Omnifit, Prolock, and Hernon develop considerable force as they cure [...]
Handheld equipment relies upon a mixture of fastener types. Critical components, such as mufflers and cylinder barrels, secure by cap screws, almost always metric. An M8 screw has a diameter of 8 mm, one thread per millimeter, and a length of 15 mm. The relatively coarse 1-mm pitch is standard for makeup to aluminum. One [...]
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