The_r1_kid wrote: ↑13 Mar 2021, 03:45
.... torsional forces from each combustion event. It seems as though GP engines and sportbikes don't bother with any real dampening like car engines do how do they get away with it, or do they?
How does the V angle effect the balance of the engine?
... How do you figure out how to size a balance shaft to smooth out an imbalanced engine? like the big bang moto gp
engines, the street going Yamaha R1, or a lawnmower.
a road car crankshaft has power takeoff at the end and a lot of flywheel at the end
so its natural frequency is low enough to need a damper
a GP or road bike crankshaft has central or other non-end takeoff and no flywheel
it behaves rather like 2 very short crankshafts would
so its natural frequency can be high enough not to need a damper
torsionals come from power strokes (but also from reciprocational inertial loads)
we know about the 1960s US Ford Indy 7200 rpm dohc 32 valve V8 (related to the production smallblock)
without a damper the crankshaft would have failed at around 6000 rpm (4th order peak) or 8000 rpm (3rd order peak)
fatigue becoming catastrophically quick above about +- 0.25 degree torsional deflection
a 90 degree (or nearly 90 deg) V angle is very handy (eg much F1 since the 1970s)
a 90 deg V twin (with right amount of in-crankshaft counterbalance) has no vibration at engine frequency ('primary')
so by extension cranks for 90 deg bank V4s with no primary force vibration can be with ....
(uneven) firing twice or once per rev eg Honda NR500 and race VFR or road VFR engines or the predictable even firing
uneven firing giving the stronger & smaller crankshaft
on M1/R1 and 270 deg twins and balance shafts etc there's been years of detailed 'discussion' in the 2 Stroke thread
and on so-called 'big bang' - whatever people mean by that
most of the detail in posts by manolis