Rotating Piston On Pin

Tech Question


Bob Currie, oakland, CA, 1968, Barracuda, Formula S, 340

The MP “A” engines book said one can turn the pistons180 degrees in the block. It is supposed to be a trade-off of more torquefor more noise.What is your take on this? Specifically: Does this affect thelongevity of the rotating assembly and pistons in particular?



Ideally, the piston pins would be centered in the pistons – which is the wayvirtually all aftermarket pistons are manufactured. But, for noise reduction(piston slap) due to the variable machining tolerances in the ’60s and 70s,Chrysler offset the pin a tad to keep the skirt “loaded” against thecylinder wall. Swapping the pistons on the pin reveres this, reducingfriction a small amount. No harm done, just a little noisier when cold.But – one very large caveat! This works safely only with low compressionpistons – ones with either NO valve clearance notches, or four (forside-to-side interchangeability.) Pistons having only TWO clearance notchesCANNOT be swapped.


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