Repairing Seized Engines
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The bottom endThis is also a good time to check the wrist pin and connecting rod bearings, as loose wrist pins or worn bearings will cause a rapping or knocking sound and will accelerate engine wear. Always replace worn or damaged bearings and wrist pins, and check the connecting rod for any damage, as well. Simply lay the rod on a straight edge or the top of a table and check to see if it's warped. And check for cracks - rods can break, so look carefully.
Before installing the rings, make sure you know which way the bevels (if there are any) are orientated, and don't forget that the gaps at the end of the rings need to be properly positioned. If the gaps are lined up in a row top to bottom you'll lose compression as combustion gases escape through the gaps. Generally speaking, you want to space the gaps at 45 degrees to each other, starting at the top, trying to avoid any overlap.
New piston rings are surprisingly sharp, so wear gloves to protect your fingers. The rings have to be expanded to fit over the piston and into the groove, and because piston rings are brittle you need to open them slowly and carefully to keep them from breaking. A piston ring expander is the best option, but you can install piston rings by hand with just a little extra care. If you have any old, unbroken rings, practice with one of those first so you can get a feel for it.
Once the rings are installed, coat the piston and the cylinder with clean engine oil. Double check that there isn't any dirt or grit in the cylinder befores installing the piston. Use a ring compressor (a large hose clamp will do just as well) to compress the rings into their grooves before inserting the piston into the cylinder. Don't force a piston into the cylinder with the rings sticking out of the grooves. This will break the rings. Gently shove the piston into place, and then install the connecting rod bearings and end cap, making sure you didn't get any dirt on the bearings. With everything back together try rotating the engine - it should rotate freely, and it will feel so good you won't stop until your arm falls off.
Contact engine enthusiast Gary W. Grinnell at 9 Laurel Pak, Northampton, MA 01060-1196.
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