Curious Crankshaft Configurations, Whys & Wherefores.

[wuzak]

The sleeves from top to bottom are certain phased 180° apart.

[J.A.W.]

Yet here: http://www.enginehistory.org/fo/FO.shtml
..it is claimed that the firing order is phased by 360`- lower bank-to-top bank..

[wuzak]

Yet here: http://www.enginehistory.org/fo/FO.shtml
..it is claimed that the firing order is phased by 360`- lower bank-to-top bank..

Yes, so the top front LHS cylinder fires at the same time as the bottom rear LHS cylinder.

The Eagle is a little confusing for me. It says they are phased together, but I don't if that means that the two front LHS cylinders fire at the same time - this seems unlikely since the rotation is opposite.

[J.A.W.]

Indeed it seems a bit difficult to discern, even for the period technical reviewers..
I have read reports that emphatically state that twin-fire was avoided in the Sabre,
& others that claim it was expected given the phasing - to get individual firing, from
24 4T cylinders it would be one firing every 30`of phased twin 12 cyl crank rotation..

[wuzak]

Indeed it seems a bit difficult to discern, even for the period technical reviewers..
I have read reports that emphatically state that twin-fire was avoided in the Sabre,
& others that claim it was expected given the phasing - to get individual firing, from
24 4T cylinders it would be one firing every 30`of phased twin 12 cyl crank rotation..

They could have but it would require the crankshaft to be phased at 30° as you said. Or 90°.

One reason why they phased the cranks together may have been to maximize clearance between the two cranks. If they were 180° apart the crank throws would be closer together at one point in their rotation. By being in phase they avoid that issue, potentially being able to bring the cranks closer.

If the cranks were counter-rotating it might work such that the crank throws are like meshing gears.

I think the phasing decision was also down to the design and layout of the sleeves and sleeve drives. By phasing them together the sleeve drives were simplified.

[J.A.W.]

The sleeve drive matter is of interest in itself, esp' the 3 large inline crank sleeve valve units..
( Bristol worked out a multiplicity of clockwork-like gear wheels for its Hercules,& X2'd it in Centaurus).
Pratt & Whitney devised their own sleeve drive system ( to avoid patent royalties, & or NIH?),
but P & W's H-24 efforts certainly ended up, like R-R's - as over-sized for the power output, vs Sabre..

Frank Halford with his prior design experience in such compact but multitudinous engines, did a good job..

[wuzak]

The sleeve drive matter is of interest in itself, esp' the 3 large inline crank sleeve valve units..
( Bristol worked out a multiplicity of clockwork-like gear wheels for its Hercules,& X2'd it in Centaurus).
Pratt & Whitney devised their own sleeve drive system ( to avoid patent royalties, & or NIH?),
but P & W's H-24 efforts certainly ended up, like R-R's - as over-sized for the power output, vs Sabre..

Frank Halford with his prior design experience in such compact but multitudinous engines, did a good job..

P&W did their own to avoid royalties, as far as I understand.

[J.A.W.]

...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...

T-C, well, if your interest is 'economy' based fine, & some do feel that 1 carb on a Triumph twin gives a
'snappier' throttle response, which they find preferable, but for performance the official `73 Triumph 750
twin 'tuning guide' actually recommends a pair of 32mm AMAL carbs, as per the sporty Norton of the time..

See: http://www.billymegawatt.com/uploads/6/ ... racing.pdf

Adit: fixed typo.

[J.A.W.]

& the equivalent Norton factory 'performance tune' guide for the Norton Commando..
..with its ropy ol' bolted up 360`crank with cast Fe flywheel 'n' all..
http://commando.yolasite.com/performance-mods.php

Twin 36mm AMAL carbs for the deep breathing 850, & clocked at 143 mph 'naked', so not too shabby..

[Tommy Cookers]

the 750 etc Norton has crankshaft offset ? - the centre head stud is rearwards of the bore centres to allow the 73mm bores for 750 cc ?
and they (in the Atlas) dropped the CR via concave piston crowns to help the crankshaft bearings

these Triumph and Norton crankshafts were modded by racers to 'toe in' the rods for reliability
the Norton crankshaft (originating in the 650SS) was used to boost capacity eg of Triumphs and BSAs
there was such a 920 cc 80 bore ? sidecar BSA c. 1977 but afaik crossplaning was then unknown to these

[J.A.W.]

T-C, there were all manner of 'development' ( engineering bodges) undertakings in getting the venerable
beast all the way from 500cc to 828cc in production form.. & up over 1000cc - in race form..

[J.A.W.]

Here is an external balance method of quelling the 'rocking couple' effects of a 120' triple crankshaft..
www.nissan-global.com/EN/TECHNOLOGY/OVE ... r12de.html

Motorcycles usually use complex & power-sapping internal balance shafts, albeit neatly hidden internally..
..but the Nissan system ought to be functional for aircraft, & snow & marine craft - which have enclosed engine units..

[J.A.W.]

In this L.J.K. Setright classic, he examines many novel approaches to the thread topic..

www.pigeonsnest.co.uk/stuff/some-unusua ... gines.html

[Tommy Cookers]

well the Nissan system would appear not to reduce vibration amplitude but beneficially to change its distribution
attractively it is just a simple and frictionless mechanism attached to the existing crankshaft
(Triumph cars once had a cantilevered weight on the gearbox casing acting as an antiphase ? NVH reducer)
I wonder where there might be a fuller explanation
maybe the engine mount scheme causes the vertical vibration to be worse than the transverse
and the balancer (ring ?) weight absorbs some vertical vibration and moves it by c.90 deg to the transverse
ie the diagrams should not be taken literally
imo it's not a million % different from my tongue-in-cheek suggestion re the TZ750

btw - Setright's 'Power to Fly' should carry a 'health warning' and indeed it does - from the author himself
similarly eg his History of the GP car generated anger in a Mr Tauranac
the 1.5 litre Brabham won on fast circuits because its drivers Gurney and JB were heavy and so handicapped on (short-circuit) acceleration
and because the Lotus had nose lift that the Brabham didn't (JB was loaned a Lotus 24 and found it rubbish in this respect)
not because as S wrote the (spaceframe) Brabham was so poor in torsional stiffness it suffered on slow corners (but somehow not in fast ones)


back to vibration ....... regarding solid mounted engines eg in motorcycles or aircraft ......
the vehicle (the series of structural elements) that the engine is solidly mounted to has a mix of characteristics
some are what we might simply call resonant ie around some frequencies they are a nil (out of phase ?) load to the flow of vibrational energy
any motorcyclist knew his vibration experience suddenly increased with rpm (additionally to the ongoing rpm-squared energy effect)
and (though less importantly) these 'non-inertia' terms will actually increase the vibration at the engine

so (imo and disputed by other views) some term modifying the vibration frequency spectrum may in this way be of some benefit
the earlier motorcycle 'swinging-arm' frames were adaptions of previous frames all basically of the diamond type ie triangulations
and so very stiff in the plane of engine vibration (but not stiff in other ways)
then came duplex frames (stiff in the other ways but less stiff to engine vibration ie more potential resonance)
eg Vic Willoughby wrote that the Dominator vibrated much more in 'Featherbed' frames - and others expressed similar views
eg AJS/Matchless twins went duplex frame and split their fuel tanks, these needed lavish elastomer mountings as a cure
eg the Triumph duplex frames were discontinued after 1 year - they broke their downtubes after a few years (on the road)
the use of higher 'balance factors' with duplex frames matches their apparent greater up/down compliance (than fore/aft compliance)
early Hondas etc intentionally had frames giving very stiff load paths to vibrational forces

[bill shoe]

Here is an external balance method of quelling the 'rocking couple' effects of a 120' triple crankshaft..
www.nissan-global.com/EN/TECHNOLOGY/OVE ... r12de.html

Motorcycles usually use complex & power-sapping internal balance shafts, albeit neatly hidden internally..
..but the Nissan system ought to be functional for aircraft, & snow & marine craft - which have enclosed engine units..

Classic Ford 302 small-block V-8's had external balancers on each end of the crank. This was lighter and cheaper than fully counterweighting and balancing the crank inside the engine. Of course when you build a performance 302, you start by throwing out the stock crank and replacing it with an internally counterweighted and balanced crank.