Another factor may be that a flat crank inline 6 engine is naturally
balanced in relation to both first and second order vibrations. So there is
no need to get tricky (or more expensive) with the crank machining.
on 2/6/01 7:23 AM, R. O. Lindsay at rolindsay@dgrc.com wrote:
> "Kai M. Radicke" wrote:
>
>> As I was trying to fall asleep last night, I began to wonder why the crank
>
> I'm glad I'm not the only gear-head that goes to sleep thinking techno-stuff.
>
>> for my inline six (TR6) motor has all of the journals in the same plane (I
>> suppose you could argue that there are two planes though). Would it not be
>> more efficient (for multiple reasons, getting at them later) to create a
>> crank shaft with journals say within three difference planes, all separated
>> by 120 degrees?
>
> The issue is primarily one of balance. Yes, the TR6 and MG "B" engines
> are single plane crankshaft designs. They are rather well balanced but
> not so much so as a 6+ cylinder. The big Ferraris use, in essence, two
> inline
> sixes sharing a crankshaft (and little else). They are really smooth.
> Another
> name for the single plane crankshaft is a "flat crank." My Ferrari 308 is
> a transverse, mid-engine V8 design but it uses a flat crank as opposed to the
> 90 degree crankshafts of American V8 engines. It's why the Ferrari sounds
> so different. In fact, the closest sound to the Ferrari 3 liter V8 is the
> Offenhauser
> V8s used at Indy back in the 60s and 70s. The Offenhauser V8 is also a flat
> crank design. The V angle is also a issue and is of course related to the
> angles
> between the planes of the crankshaft -- if there is more than one. Some of
> the
> V12s are 60 degree Vs. The Formula one cars are V10s! Want to work
> out THAT balance problem?! Yikes!
>
>> Is there some reason why multi-plane cranks are not more popular (again,
>> like I said I know nothing about modern day motors)... ? Obviously, I am
>> not talking about motors with V blocks either.
>
> So to sum up; Four cylinders, four stroke Otto Cycle engine, power stroke
> every OTHER stroke and, in the advanced designs, V angle. It's about balance.
> Balance makes the engine more manageable to use and it also minimizes wear.
>
> Rick Lindsay
> Diamond Geoscience Research
> 5727 S. Lewis Ave., Tulsa, OK
> Voice: +1 918-747-3456
> Fax: +1 918-747-8599
--
Max Heim
'66 MGB GHN3L76149
If you're near Mountain View, CA,
it's the red one with the silver bootlid.
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