for a yz250 trailrider with a little abuse?
Try the search function and make some coffee because you will be reading for a while.
Each has its negs. And benefits.
i use whatever is best price on ebay now adays. I used to use pro-x constantly but they cut back on alot of the overbore stuff for the CR250. The Wiseco Pro-lites are nice...
Cast and Forged, had no problems with either
A cast piston is manufactured by pouring molten metal into a mold. The final shape is machined to it's final exacting tolerances.
A forged piston is made by taking a chunk of metal, and beating it into shape with a die-press under enormous pressure. Like casting, the final shape is achieved through precise machine work.
The main difference between a cast and forged piston is the grain structure. A forged piston is beaten into shape, and as a result the metal stretches and compresses as the piston takes shape. The varied, elongated grain structure is like fiber reinforcing, and it makes for a very strong piston. Microscopic cracks don't readily propagate through the structure of a forged piston due to the high density and the irregularly spaced and sized grains.
A cast piston, on the other hand, is made up of grains that are all the same size, because it starts out as a liquid that, after being poured into a mold, undergoes a controlled cool-down process that allows the metal to reach a near-perfect equilibrium right out of the mold. The highly regular grain size and distribution makes them more prone to crack propagation and failure.
The break-in of the two types is very different, because the metal properties are very different. The forging process produces a lot of internal stress from beating the metal into the intended shape. The stress is trapped in the metal of the finished part. A cast piston has lower internal stress, because it was able to seek it’s own internal equilibrium as the liquid metal flowed around inside the mold and then underwent a controlled cool-down. Since a cast piston has lower internal stress, it won’t distort nearly as much as a forged piston will when heated to a high temperature.
Forging produces a higher grain density than casting, making the part much more durable under high-heat, high-load conditions. As long as you are patient enough to break a forged piston in correctly, you will have a piston that is more durable under extreme conditions.
All the OEM's use cast pistons in their 2-strokes for good reason.
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