Curious Crankshaft Configurations, Whys & Wherefores.

[J.A.W.]

At the behest of T-C, & to avoid off-topic drift on the specific/dedicated threads...

Now T-C, some 0`vertical twins run a pseudo-V-twin crankpin layout, but these are in general lazy
running 'showboats'.. whereas 'real deal' units such as the current BMW, run a 'true-school' 360`crank..

The original Norton Commando, notwithstanding its 'ropy' built-up 360`crank, was successful in its own right..

Prior to the advent of the 'isolastic' chassis vibe-quelling Commando, an Aussie ex-Vincent engineer
by the name of Irving proposed a 90/76 degree crank as a method of settling the bigger vertical twins..
Yamaha, with their odd Brit-bike fetish, 1st tried to out-do the arcane, but clever Commando by means
of complex ( & poorly executed, engineering-wise) counter-balance shafts in their ( dud) TX 750 twin..

Since that debacle, they tried 180`( in the smaller, but also 'too clever by 1/2' TX 500 ) as
smaller Nippon 4T vertical twins have fairly commonly used, but it does not scale up well, nor
does it offer a 'natural' feel.. they present as busy, & with a dissonant unpleasant tone..

Yamaha went on to make a 500 single , with oil-in-frame chassis ( BSA B50-like, but soft) a 120`triple,
( BSA/Triumph-like, but too fat, fussy & fragile) then a Vincent-like XV-1000 complete with vestigial frame & cantilever rear suspension, that failed in the showroom, until 'chopperized' into an H-D wannabe..

The traditional narrow angle 45`H-D does indeed offer a dirt-traction 'friendly' irregular impulse,
certainly, ostensibly more modern Ducati 90`V-twin mills were tried, but could not match the XR-750..

[Tommy Cookers]

Irving's suggestion (going from the '0 deg' crankshaft to a 76 deg one) yielded .......
only about 21% reduction in peak vibrating force at primary (engine rpm) frequency
and (broadly) eliminated ........
vibrating forces at secondary (twice engine rpm) frequency (but these were anyway only a quarter of the primaries)
variations in crankshaft torque due to inertia of rods & pistons
(so ? - these are trivial compared to torques from power strokes - firing 284 deg then 436 deg would demand more flywheel for town speeds)

the modern take on this (started in the Yamaha Tenere) is the 90 deg crankshaft ......
if without counterbalance shafting this would reduce peak primary vibrating force by about 28.5% (and secondary by about 90%)
on the basis as above, the flywheel would need increasing (but in the interests of high-rpm shifting presumably doesn't get it)
but the modern way is to add counterbalance shafting
the 90 deg crank means less 28.5% less of this is needed with a further benefit as single shafting gets closer to the (impossible) ideal positioning
given that Triumph make 0 deg and 90 deg crankshaft versions of one machine an interesting comparison might be possible

of course parallel twins of 650cc and less all use the 180 deg crankshaft ......
(on its own this would give perfect primary force balance but a smallish moment 'couple' imbalance)
but it's combined with a couple counterbalance shaft to cancel primary moment 'couple' imbalance (TX500-style, Suzuki's takeup c.1978 widespread)
not surpising as the ride-to-work 250s now do 13000 rpm
essentially the of vibration signature a 4 cylinder engine of similar size. secondaries remaining untreated except in the largest 4 cylinder machines

regarding the now-traditional 180 deg without counterbalance shafting .....
135-150 deg would maybe offer a better compromise between uneven firing, and primary vs secondary imbalance
(though elastomer engine mounts are rather good where the designer doesn't decide to use the power unit structurally}
the simplest 180 deg crankshaft would be shaped such that it has mass balance but it's own moment imbalance when rotating
adding to the unbalanced couple from rods&pistons at tdc and bdct but Honda of course included crankshaft counterweighting of this
if this was over 100% counterweighting it would have reduced tdc and bdc moment 'couple' vibration at the cost of some vibration midstroke
https://images.cmsnl.com/img/products/c ... 1_137a.jpg


but these current 180 deg twins having a (primary) couple counterbalance shaft (which works by having its own couple imbalance of course) ....
have the crankshaft also (primary) couple imbalanced (by overweighting) thus
http://world.honda.com/CBR500R-CB500F-C ... age02.html
such that .....
at tdc&bdc couple balance shaft's p couple imbalance adds to crankshaft's p couple imbalance to cancel exactly the p couple imbalance from pistons&rods
around midstroke the the balance shaft's couple imbalance cancels the crankshaft's couple imbalance (as they are in opposite rotation)
and the piston& rod primary couple imbalance is around nil
job done !

and we should remember that the valve reciprocation also produces vibrating effects though this is usually ignored as inevitable

[J.A.W.]

T-C to be fair, the 180` crank is generally used in 'cheapy', or 'learner' twins as an economy unit,
& so the owners put up with the inherently unpleasant aural/tangible aspects..
.. or buy a single or V-twin, instead..

Honda, Kawasaki & Yamaha - in the past - did sell smaller ( ~400 cc) vertical twins with 360` cranks..

& none of the large capacity staggered crankpin vertical twins are really performance orientated either..

Even at 961 cc, the faux-sporty 'new' Norton Commando..
..cannot best the 1/4 mile sprint figures set by its antiquated but punchy, namesake..

& AFAIR, Irving did consider the 90`off-set, but felt the inertia torque advantage of 76`was worthwhile..
..but of course this was an ' mental/on paper' exercise only, so its not a real surprise for the likes of Yamaha.. ..working in-metal & with decades of experiential/empirical testing of complex rotating shaft-balancers..
..to decide on the 1/4 circle/90`crankpin set-up as their production (& 'crossplane' catchphrase*) choice..

( *although its a little rich IMO, for Yamaha to attach that marketing speak term to their 3 cylinder mills,
even if technically applicable, since 120`cruciform crankpins are traditional SOP for triples)..

[Tommy Cookers]

well .....
Irving would have needed his engine to run with 1 carburettor, as twin carbs were inconceivable in those days
76 deg should have helped with this

the steam railways actually had real inertia force effects (not having transmission damping and soft pneumatic tyres)
and the same BB crankshaft vs non-BB crankshaft arguments that were also never settled

even engines with on a rigid frame 2 independent sets of driving wheels that would suddenly or slowly go in and out of phase
so likewise the vibration addition/cancellation and the BB factor

normally engines (having double-actingcylinders) had 2 cylinders with 4 power strokes per rev or 4 cylinders with 4 power strokes per rev
rather rarely 3 cylinders with 6 power strokes per rev, and (almost unknown) 4 cylinders with 8 power strokes/rev

[J.A.W.]

Dunno about the claim that Irving "...needed to run with 1 carburettor..." T-C,
after all, unlike the other contemporary ~litre capacity bike engines of the day ( Squariel/H-D/Indian),
he'd always used 1 carb per pot on 'The Vincent', as did the sporty, high-output vertical twins (T120/A65L/SS/W2)..
..for which the intrusive/destructive vibes were more of a concern - than on soft-tune 'cooking' models..

[Tommy Cookers]

afaik Irving was taking his ideas round the industry in the 1940s when it was designing parallel twins in response to Triumph's lead
twin carbs didn't start to appear on such road machines till about 1960
the Grand Prix (Triumph's racer) didn't have splayed inlet ports, it didn't even have splayed exhaust ports (being originally a fan-cooled genset)
twin carbs ie splayed inlet ports appeared as a special race part in 1956 ie as on the Johnny Allen streamliner record
twin carbs on the road were a pain in the wrist, and a waste of money and fuel

btw a few sidecar racers in the 60s converted their Triumph engines to 180 deg cranks, but nobody 'Irvinged' anything till decades later
180 deg cranking is not historic race-legal unless using actual historic parts, maybe Irvingisation is ???

Doug Hele said of the 750 twins (1973 ?) that the noise-regulated exhaust systems rendered pointless the twin carb option, but people expected them
my single-carb 750 was more economical than almost anything else over 250
what some might call response also showed as gaining or losing 2 mph on motorway (freeway) hills where cars gained or lost maybe 7 mph
(and RD 350s irritatingly gained or lost 15 mph, far worse than the earlier R5 or the Suzuki 500 or 4 stroke 250s etc)
we still had friction-hold in road twistgrips then, before some US Government Agency banned them
though of course the US-mandated mirrors compelled rubber-mounted bars and so helped all manufacturers vibrationwise

our old British 350 singles had been super economical and less vibratory than eg related 500s due to their smaller and much lighter pistons
except the Velocettes (from Irving's Velocette period) which we now find had their 72 mm pistons deliberately made to the 500s 86 mm piston weight
so that the 350 and 500 crankshafts could be identical in all respects including their counterweight mass

[J.A.W.]

Nah, T-C, I can't concur, 'bout the twin carbs, a single carb is ok for a 'cooker', sure,
but if its more performance you want, then one simply can't keep up..

If one was better, then it would've been a 'production' Triumph Trophy Thruxton which did a ~100 mph lap
at the IoM in `69 rather than a Bonneville.. ..like-wise, Doug Hele developed the utility Norton Dominator,
into the 500cc Domiracer, which also lapped the IoM, at ton-up speeds.. ..with twin carbs..

Hele later developed Turner's cheapo unit 500 Triumph into a racer capable of winning the Daytona 200,
& even placing 2nd to Ago's factory MV-3 at the fast Spa G.P. in `69 too..

The `74 750 Triumph twins were handicapped by a soft-tune cam set-up/stifled pipes, for noise reg compliance,
which tended to blunt the twin carb effect, whereas the 1st 724cc of`73 - had proper Bonneville cams,
& rorty mega-style pipes..

'Splayed' inlet Triumph heads were really a bit of a sales hype gimmick, Nortons never needed them,
& even with its longer stroke/smaller bore dimensions the excellent breathing capability of the 750
Commando left all stock production/road spec Triumph twins in its ( always twin carb) speed wake..


I can also attest, having built a 'defacto' Triumph Adventurer, (using an OIF BSA B25 chassis fitted with a tuned 500 Daytona mill) , that twin carbs do flow more HP..
.. a stock soft-tune single-carb Adventurer was a breathless, insipid thing by comparison..

As for the good ol' Velocette 500, - while they look antiquated, unusually for such a Brit, it ran to
a 'square' 86mm X 86mm bore & stroke, & could see off most of the other 4T 500s of its era..

In a similar vein to the 350/500 Velo crank commonality balance, Honda built a 250 2T triple,
the MVX, (to ride on the back of Freddy Spencer winning Honda its long coveted 1st 500 G.P. title on a 2T/3),
& to get the required balance, used a special heavy conrod/piston in the middle of their off-set V-three..

BMW in their current 800cc vertical twin, run an even-fire 360`crank, but use a 3rd 'dummy conrod' *,
(similar in principle to the Honda), in lieu of any complex balance shaft set-up..

* A fix, also previously mooted by British engineers, for the Triumph twin..

[wuzak]

..when R-R built a 'Chinese' copy of the Napier Sabre H-24 aero-engine, they
made some crucial changes, such as having the superimposed twin 180`V12-type crankshafts
run in opposite rotation, linked via a simple spur-type gear.. & with paired cylinders firing together..

..which caused repeated failures of the magneto shaft drive, due to the torsional harmonics..

The Sabre ran its similar crankshaft layout but rotating in the same direction, & phased 180`apart,
so no two cylinders fired together, & they were geared together via a more sophisticated compound balanced unit.. -
..& so avoided the damaging fatigue caused by harmonic 'chatter' - which plagued the ostensibly more simple (& traditionally functional, as used in their V12s ) R-R set-up..

I wish you would stop with this "Chinese copy" BS. If it had truly been a Chinese copy it would have been closer in all respects. It shared the configuration, but not much in detail.

TV may have caused the magneto drive failure, but the use of the spur gear was likely not an issue.

In the case of the Sabre the balancing mechanism was to keep the four pinions in even contact with the single output shaft gear. This was not at issue in the Eagle.

If simultaneous firing was the issue then they could have phased the engine halves differently.

Allison used a simple spur gear to connect the two halves of the V-3420 when running with counter-rotating crankshafts (the V-3420-B). The V-3420-A running with crankshafts rotating in the same direction, phased by the reduction gear on the output shaft.

[J.A.W.]

..when R-R built a 'Chinese' copy of the Napier Sabre H-24 aero-engine, they
made some crucial changes, such as having the superimposed twin 180`V12-type crankshafts
run in opposite rotation, linked via a simple spur-type gear.. & with paired cylinders firing together..

..which caused repeated failures of the magneto shaft drive, due to the torsional harmonics..

The Sabre ran its similar crankshaft layout but rotating in the same direction, & phased 180`apart,
so no two cylinders fired together, & they were geared together via a more sophisticated compound balanced unit.. -
..& so avoided the damaging fatigue caused by harmonic 'chatter' - which plagued the ostensibly more simple (& traditionally functional, as used in their V12s ) R-R set-up..

I wish you would stop with this "Chinese copy" BS. If it had truly been a Chinese copy it would have been closer in all respects. It shared the configuration, but not much in detail.

TV may have caused the magneto drive failure, but the use of the spur gear was likely not an issue.

In the case of the Sabre the balancing mechanism was to keep the four pinions in even contact with the single output shaft gear. This was not at issue in the Eagle.

If simultaneous firing was the issue then they could have phased the engine halves differently.

Allison used a simple spur gear to connect the two halves of the V-3420 when running with counter-rotating crankshafts (the V-3420-B). The V-3420-A running with crankshafts rotating in the same direction, phased by the reduction gear on the output shaft.

W, if wishes were duplicate magneto drives, the R-R H-24 Eagle might've lasted a few more flight hours..
& you might not be aware that 70+ years ago 'Chinese copy' had a different meaning..
..but if you prefer, then perhaps 1/2-arsed plagiarism will do, & that aint no "BS"..

So W, you've put up a somewhat off-topic post here, but no answers to the problems..

Can you provide any root-cause analysis of the reasons for R-R's 'Sabre reiteration' mechanical failures?
If not, then what is your best guess? & what reasoning do you use - to dismiss the overt difference?

Also, AFAIR, the H-24 Eagle did not introduce any novel crankshaft configurations, although R-R did have
problems with Griffon crank, necessitating palliatives such as a firing order change,
& add on crank-balance dampers..

Like the R-R H-24, the cobbled together Allison never received regular service clearance,
in effect ever only flying short hops in experimental aircraft, unlike the Napier Sabre..
.. so it was hardly a 'proven' aero-engine, either..

[wuzak]

I figured this was the place for the discussion, as it is largely where you have continued your "big bang" OT discussion from the Honda thread.

I do not know or claim to know what caused the issues with the Eagle.

I do know that they didn't spend as much development time as the Sabre had on it before it became reliable.

The V-3420 had an on-again, off-again development. It did do some time in the XB-19 as a trial installation for the XB-39. But none of the aircraft that it was selected for went into production.

There were some firing order issues that were solved by changing the phasing between the two engine halves.

Also, the V-1710, and consequently the V-3420, had TV dampers on the crankshaft.

[J.A.W.]

Fair enough W, here then is the 'Flight' article on the R-R Eagle 22;

http://www.flightglobal.com/pdfarchive/ ... 00626.html

The technical illustration clearly shows the simple spur gear coupling of the twin counter-rotating cranks,
which featured a pair of cylinders firing simultaneously - quite a bit of an 'ask' for a single spur gear's mesh..

Certainly, when 'big-bang' firing configurations were tried on racing motorcycles, the PTO/primary spur gears designed for evenly divided regular torque impulses often failed, & required redesign/'beef-up'..

While the Allison V12 required crankshaft redesign to include such things as full counterweighting,
Napier's Sabre, by contrast, was found to be well balanced enough to delete the original full C-W scheme..

The graphic linked below shows the Sabre's much more substantial crankshaft coupling/PTO arrangement..

http://www.hawkertempest.se/index.php/c ... o-pasquale

[wuzak]

James, from that top animation the crankshafts are in phase, not 180° apart. Which means that cylinders go to TDC in groups of 4. Which means that 2 must be firing at the same time.

Are they wrong or are you wrong?

Generally speaking the Rolls-Royce engines did not drive the reduction gear directly. Instead they used a torsionally flexible shaft. This system may, possibly, have been used in the Eagle.

[wuzak]

Indeed, the upper crankshaft is connected by a "floating coupling".

https://www.flightglobal.com/pdfarchive ... 00629.html

And it looks like the magneto drive is driven from the sleeve drive, which is driven from the rear of the engine, not the phasing gears or the reduction gears.

I know there was some issue with the magneto drive, worsened by the fact that there was only one, but was there any issue with the reduction gears themselves? Or the sleeve drive?

[J.A.W.]

James, from that top animation the crankshafts are in phase, not 180° apart. Which means that cylinders go to TDC in groups of 4. Which means that 2 must be firing at the same time.

Are they wrong or are you wrong?

Generally speaking the Rolls-Royce engines did not drive the reduction gear directly. Instead they used a torsionally flexible shaft. This system may, possibly, have been used in the Eagle.

Wayne, I would accept the information about the Sabre's 180`crankshaft phasing from the maker,
- rather than read too much into a basically illustrative latter-day animation, wouldn't you?

As per R-R, 'trouble' with their simple spur gear arrangement..
.. with those immense & complex forces fed through so few teeth in mesh, seems in hindsight, plain as day..

I dare say Frank Halford would've pointed it out, back then though, too..

AFAIR, LJK Setright noted Eagle 22 reduction gear problems amongst his list of objections..
( along with excessive dimensions for out-put) in his book, 'The Power to Fly'..
..one of those books that I regret 'lending' - & never getting back..

& while the Sabre itself had many ( usually production, rather than in actual design) problems,
the crankshaft coupling/final drive unit & ( also single shaft) mag-drives - were not an issue..
..indeed the Sabre featured a long quill ( torsion bar) shaft to cushion its sleeve drive shaft
..whereas the Eagle 22 has only a very short one on the shaft leading to the mag drive gears..
..which are located very close in the crankcase to - that dubious - spur gear crank coupling..

[wuzak]

It seems odd to go to the time and expense of modelling the engine, then to get the phasing wrong. Even so, with 180° phasing you would have two cylinders on the left hand side upper and two cylinders on the right hand side lower getting to TDC at the same time, so still 2 cylinders firing at the same time.

They certainly look to be in the same phase according to drawings:



https://s-media-cache-ak0.pinimg.com/or ... faaa23.gif



Halford also designed the Rapier and Dagger with two cranks, though, obviously, not as powerful as the Sabre or Eagle 22, they used a simple spur gear reduction system, though it looks like they were connected via the single reduction gear with the crankshaft pinions either side, the crankshafts rotating in the same direction. Similar to the V-3420-A, in fact.

Apparently the V-3420 was mechanically sound, but suffered from uneven fuel mixture distribution from one side to the other, probably due to the arrangement of the supercharger and unequal length runners.

As for Rolls-Royce, it is interesting to note that the cam shafts were driven from the back of the Merlin, while they made a point of running everything, including the supercharger, off the front of the Griffon. They had issues with the supercharger drive and switched that to run off the rear of the crank, but the camshafts, magnetos, etc., ran off the front.

I suppose the sleeve valve engine has less of an issue with the potential of catastrophic interference than do poppet valve engines.