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Old 02-19-2021, 03:12 PM   #12 (permalink)
Isaac Zachary
High Altitude Hybrid
 
Join Date: Dec 2020
Location: Gunnison, CO
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Avalon - '13 Toyota Avalon HV
90 day: 40.45 mpg (US)

Prius - '06 Toyota Prius
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Quote:
Originally Posted by freebeard View Post
....at least in boxer configurations. The various masses rotate in unison, but they can trade momentum which results in internal vibration.
In inline-4's the two outer pistons go up as the two inner pistons go down also canceling each other out. On a boxer the pistons aren't exactly across from each other an so do induce a little vibration.

I could be wrong, but from what I understand counter weights on the crank shaft are to counteract the centrifugal forces of the big end of the rods and the rod journals, not the reciprocating forces of the pistons.

Have you checked out Driving 4 Answer's recent ongoing series on engine balance?
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