under item 5 they claim drilling more than 2 holes in a V8's end counterweights will create a "secondary wave" that will cause the crank to flex and fatigue, and maybe the nose to break off.
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secondary wave in V8 crankshafts
- Thread starter Tmoose
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MikeHalloran
Mechanical
Yeah, the assertion sounds a little empirical, but I'm sure they've drilled more crankshafts than I have.
Mike Halloran
Pembroke Pines, FL, USA
Mike Halloran
Pembroke Pines, FL, USA
GregLocock
Automotive
In production balancing units have strict limits on how many and how deep the holes are allowed to be, but if they are not deep enough to meet the big end or main radius then frankly they would ply no part in the load path.
BUT
typically people only drill the end webs of the crank, this means that although the crank is two plane balanced, when it is running the misdistribution of inertia will cause additional internal forces, usually reacted at the main bearings. So if you want to do the job properly, treat it as a flexible rotor, and monitor the main bearing forces as you balance, at the right speed. Counterweight design is optimised to minimise these forces, balance holes will upset that strategy.
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376
BUT
typically people only drill the end webs of the crank, this means that although the crank is two plane balanced, when it is running the misdistribution of inertia will cause additional internal forces, usually reacted at the main bearings. So if you want to do the job properly, treat it as a flexible rotor, and monitor the main bearing forces as you balance, at the right speed. Counterweight design is optimised to minimise these forces, balance holes will upset that strategy.
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376
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