The hole is offset from the piston's center slightly so that when the piston and rod reach TDC, they do so at slightly different times. This hole accepts a pin that connects the piston to the connecting rod. They support the shock loads the rings receive during combustion. They are similar to the lands in a gun barrel. The solid pieces between the grooves are called ring lands. This helps the groove stay clean of carbon. In the four-stroke engine, natural harmonics cause the ring to rotate as the piston goes up and down in the cylinder. The closely manufactured groove accepts the third part, the precisely made piston ring. Moving down the piston, the next thing is the ring groove. It must therefore be quite thick so as to not collapse, though it is not always the thickest part of the piston. Consequently, the crown is the hottest part of the engine after the spark plug. The piston's top or crown takes the brunt of combustion's forces and heat. The piston is made of essentially seven parts. In fact, nearly 80 percent of the cylinder's excess heat is drawn away by just the piston's rings. Finally, the piston is a heat conductor, transferring some of the cylinder's heat to the outside. The piston is also a seal, as it seals combustion's forces and compression's trapped air. It is a bearing, receiving loads from combustion and transferring them straight and true through the connecting rod to the crankshaft. Following is just a brief outline of the piston's function and construction. It may be the hardest-working part in the internal combustion engine. The piston is under-appreciated, for sure. A person can't be as dogmatic as they would like, and anyone who is insistent just doesn't know the facts. During the 1970s it was a frequently debated topic: The answer used to be simple, because one type of piston was in fact better than the other. Which is better, the cast piston or the forged piston? This argument doesn't come up as often as it used to. This is a hot topic and I expect some very informed argument will come from this but do your homework because the cast pistons of 25 years ago aren't what they are todayl. The article was wrote and researched by Mike Varse but worth keeping in it's original content rather than summarizing it. (In most applications ).īelow is some research I put together and thought I'd pass it on. But the cast pistons seem to have a better life because their ability to disapate their heat over the entire surface is a lot better than a forged. In short, I don't see why their cast pistons are the wrong choice for their engines that they sale at a greatly reduced price than most others, who want upwards of $5000 dollars.Įach on these piston types have their own place in the world of efficient engine combustion and from what I read, the forged pistons are best used in modified engines. I've come across several posts that mostly have to do with the 4-TEC engines and SBT using the wrong pistons when it comes to the OEM remanufacturer of these engines.
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