Crankshafts can be balanced unless they are of a really
bad design. Many racing crankshafts have the counterweights
cut down to reduce weight and rotating mass on high rpm's.
Counterweight mass is less (whatever?) important for inline engines.
Thomas
Ofarrell, Fergus wrote:
> Tony, (see message below)
> The whole idea of fully vs. partial counterweighting only relates to
> performance in terms of the potential for shaking, (non-balanced masses
> being spun at high speed) and the vibration causing harm to bearings,
> leading to short bearing life. The thing is, of all the people who have
> done this, and those who have driven their cars, none have reported strange
> quivering at particular rpm's, or "I drove for 6 months and my dentist said
> my teeth were coming loose" sort of stories. So this could mean a few
> things: (please, others correct me if I have missed something important)
> 1. bearings sufficiently over-designed that their life cycle not compromised
> by rotating un-balanced mass H-20 vs. balanced U-20
> 2. engine mounts are gooey enough that vibes not transmitted (although
> revving with hood open would have raised questions from those in the know),
> so the vibes exist, but something else (like the timing chain) breaks first,
> so the effected parts get changed before life cycle is reached
> 3. we vary the rev's so much in our driving (flashback to Palomar Mt. Road)
> that the harmonic vibes never really get time to set up resonance, which is
> (usually) far more destructive.
>
> What the heck, everyone says it works fine and nobody mentions short life,
> so while we all could talk about numerous things that could be, these ones
> don't seem to happen. I would heed their 'complete system' installation, and
> use the same oil pump vs. crank set-up that has worked previous. It may be
> that the lower oil pressure forklift set-up goes with lower temp oils, while
> higher temp car oils and higher revs may need the U-20 oil pump. That may be
> a key to longevity. Okay so maybe "15,000 RPM" Victor Laury can test
> endurance better than me, (110k miles on my Ford, still original front brake
> pads) but there are lots of supporting H-20 installations, which is better
> proof than the "worst case scenario" warning of impending doom.
> (sorry Victor, I couldn't resist. Clandestine reference to mis-typed 5,000
> rpm statement.)
>
> Fergus O, 69 2000 (forget "I wanna be like Mike, I prefer "I wanna drive
> like Victor")
> _________________________
> Date: Tue, 06 Mar 2001 15:45:19 -0000
> From: "Tony Genovese" <chaztg@hotmail.com>
> Subject: H 20 vs. U 20 bottom end
>
> ...... being that the U series crank is
> fully counterweighted, whereas the H series crank is not?
> Is this a noticeable performance defecit if one uses the H series crank in a
>
> street motor?
> Tony Genovese
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Thomas in Sweden
Nissan Silvia 1965 x2
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