300cc Kit

[Duckati]

Originally Posted by Weldangrind

No disrespect intended towards Peter, when I say that perhaps the piston was 180* out from proper orientation. So hard to know, since the piston top could have spun when things came apart.
The arrow on the piston points roughly 80* to the right from forward, which means it could have spun 120* from rearward. The intake and exhaust valve reliefs appear to be identical, so it would be an easy mistake to make, if a person didn't spot the arrow. Again, no disrespect intended.

Really interesting thought... To my eye, the reliefs at bottom of your picture slightly larger. The skirts often aren't symmetrical either:

“On asymmetric piston designs, there is a wide skirt panel and a narrow skirt panel,” he explains. “The wide panel needs to be in the direction of major thrust. The major thrust direction is the side that is against rotation. For example, if the engine rotates clockwise when viewed from the front pulley the major thrust would be to the left (against rotation).”

(borrowed from http://blog.jepistons.com/piston-ori...ps-and-bottoms)

Peter had noted the ~50g or nearly 20% weight increase over the stock piston, despite someone here saying they should be within 3% as a general rule to match crank counterweight balancing, so that's where my brain had gone. Folks here had requested purchasers of the kit to weigh theirs before installation, but I'd not found anyone that did when reading this whole thread yesterday. Perhaps someone did but forgot to mention it...

Anyone? Bueller?

...but the fact that no one else has reported a change in vibration, yet Peter's was extremely noticeable to the point he was considering going back to stock, has remained a red flag in my brain.