Curious Crankshaft Configurations, Whys & Wherefores.

[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..

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.

Ford has offered their ~5 litre V8 in a number of different iterations, which even on the basic pushrod types
involved alternative firing orders, now of course they do a 'flat plane' crank in the OHC V8.

This article: www.enginelabs.com/engine-tech/cam-valv ... ur-engine/
looks at the matter..
( & while mainly V8 oriented, also appears to dismiss the 1-5-4-2-6-3 suggestion for a 90`V6, recently mooted per F1)

[Tommy Cookers]

this is a good read
http://www.titanicology.com/Titanica/Ti ... eMover.htm
at that time the Yarrow, Schlick, and Tweedy method for the crank geometry was favoured
https://www.google.com/patents/US594289
but this seems to be the comprehensive view
http://www.sname.org/HigherLogic/System ... 3e4129d611

[J.A.W.]

Indeed T-C, the very apotheosis of recip' steamship propulsion & an early 'hybrid' to boot..

That crank angle configuration appears oddly similar to the offset X angle as used by the Napier Cub..
..the 1st 1000 hp rated aero-engine.. https://oldmachinepress.com/2012/12/22/ ... ft-engine/

[Tommy Cookers]

fwiw I assume that ......

the Cub had bank angles arranged so the pilot could see where he was landing (as eg the Liberty was a 45 deg V12)
balance would anyway be good

like all steam engines the Titanic's had crossplaneish crankshafts for starting etc reasons ie a car-type crank would have dead zones
there was compromise between angles for balance and the angles needed for steamflow timing and power sharing by the cylinders
the timing is somewhat like a compound locomotive's (eg the LP cylinders apparently don't act synchronously)
compromise was always unavoidable, though denied, as was the vibration of compound steam reciprocating marine engines
(the earlier triple expansion engines, having 3 cylinders, cheerfully and falsely claimed to be vibrationless)
treatment of the weights of the very different sized pistons was part of the fashionable design doctrines

early turbines eg Lusitania were ungeared and so very inefficient at low speed rpm (though incorporating a reverse turbine hadn't been a problem)
gearing was soon introduced so that the turbine rpm of subsequent ships was higher overall

[J.A.W.]

T-C, re: the Napier Cub, notwithstanding that it was a seemingly capable engine looking forlornly for a useful role..
..since contemporary airframes were basically too primitive accept its size & power, to functionally useful value..

( Perhaps the British R-101 airship should've had the Cub - instead of monstrously over-weight/under powered CI mills).

Anyhow, the Cub does stand out as one of the few X-configuration engines - to have been a basically trouble-free runner.
Is the asymmetric angled architecture, a clue - to this unusually good conduct?

Curtiss did build a * pattern ( like 6 Sunbeam S7's en bloc ) that ran well enough, 'cept that it was air-cooled..
..but insufficiently so.. ( as per Sunbeam, too). https://oldmachinepress.com/2012/11/09/ ... ft-engine/

As for turbines in ships, these days gas-turbines - very similar to the large aero-engine units which are used in on-demand power generation plants - are also used in warships for 'sprint mode' capability - ( CI engines are still more
fuel efficient for normal 'steaming' progress ) as well as for power generation in new-fangled roles such as rail-guns..

[J.A.W.]

Brian.G kindly posted some excellent photos of an F1 engine timing gear cover.. thanks Brian..
Well of course, there are timing gear sets, & then there are 'horological' level timing gear sets..

Behold, the mighty Bristol sleeve valve radial, with myriad gear-wheels arranged about the central crankshaft:

[J.A.W.]

On another thread in the E,T & C section - the application of torsional vibration dampers to F1 cam-drives is discussed..

Here below, from 3/4's of a century ago, 'Flight' considers the application of such dampers to aero-engine crankshafts:

http://www.flightglobal.com/pdfarchive/ ... 00076.html

[johnny comelately]

Slightly off topic, but does anyone know of a crankshaft nut design that uses slightly different thread pitch between male and female to stay done up?

[63l8qrrfy6]

Which joint precisely?
If it's designed and torqued correctly it shouldn't loosen.

[johnny comelately]

The large single nut on the end of the crankshaft that might hold on a pulley or gear or balancer.

[63l8qrrfy6]

It shouldn't come loose. Is the male thread on the crank then?

[Tommy Cookers]

those nice Hirth people made built-up crankshafts pulled together by such differential threads
and presumably patented the design

[johnny comelately]

those nice Hirth people made built-up crankshafts pulled together by such differential threads
and presumably patented the design

Yes Tommy, I knew they had a coupling design but not the different pitch idea, so thank you.

[63l8qrrfy6]

those nice Hirth people made built-up crankshafts pulled together by such differential threads
and presumably patented the design

Yes- I think it was used on either the mercedes w25 or w125 (or both?). I saw the cranktrain displayed in a museum in Germany, impressive craftsmanship for that time.

[Tommy Cookers]

Irving suggested his 'magic' 76 deg crankshaft to the UK makers of 0 deg crankshaft parallel twins - without success
and it would have given little relief from primary frequency vibration

more recently historic race UK machines have had eg 90 deg or 180 deg made from (3 piece bolt-up) Norton crankshaft bits
I suggested here that 135 - 150 deg would be better

50ish years ago BSA/Triumph started making 3 cylinder 750cc machines with 120 deg 1 piece crankshafts
while still making 'old hat' and very vibratory 0 deg 500cc and 650cc twin cylinder machines
the 3s boosted credibility, seeming new and exciting and performing well and with much reduced vibration


they could have used the 3 cylinder as a basis for simple and cheap improved twin
this could be confirmed now ie by cutting down a 3
the 3 has a 3 piece 'salami- style' crankcase (the twin would use 2 of these)
the 3's crankshaft and camshafts etc would be cut down
(the crankshaft could have 3 mains/4 crankcase pieces or 2 mains/2 pieces stiffening added to redundant journal)

a relevant exercise in industrial archaeology- and easier than alternatives

with the 120 deg crank the primary and secondary vibration would be half (the then-existing 500cc twin's)
it would have slung less oil
the machine's sound would have been new and related to the 3 and so better imagewise

a better proposition than Irving's