Alternate crossplane V8/I4 crankshaft implications

[Lapislignum]

Hi all,

I've been pondering crankshaft orientation for a while and am trying to work out why all V8 crankshafts are "up left right down" and not "up down left right"

Intuitively and based on fairly simple calculations it appears that the latter configuration would reduce the first order rocking couple and perhaps allow a lower inertia crankshaft (though maybe less effectively than just putting on a light flywheel) but it also introduces a second order rocking moment, which might be the reason they aren't built this way? then again I5s have higher order rocking moments, but of smaller magnitude.

A Kawasaki patent for a supercharged crossplane I4 has the crankshaft arranged in the non-traditional way in a diagram, but it isn't really mentioned in the text.

I made a video of this arrangement, not sure if youtube links are frowned upon here.

 

[TugboatEng]

I wouldn't call cross-plane inline cranks non-traditional. They have been standard fare for nearly a century in 2-stroke inline engines and parallel-plane in V engines. There is a fore and aft rocking moment. Counter-balance shafts handle that.

Ford has recently adopted a parallel-plane crank in their V8 engines.

Yamaha started this trend with their R1 engine. I have one personally with their MT-10. Honestly, I think it's all about marketing as the oddball crank arrangements have very unique sounds.

 

[Lapislignum]

Dang, lost my reply.

Cheers! I'm not talking about using crossplane crankshafts in place of flatplane crankshafts, just wondering why nobody has tried an alternative crossplane configuration. While they aren't common, the pros and cons of inline 4s with crossplane crankshafts are fairly well understood.

The Ford voodoo leads me to believe first order rocking moments aren't the end of the world. Maybe I'm trying to solve a problem yaht doesn't exist. Again.

 

[TugboatEng]

The inline-4 cross-plane crank is in one of the most mass produced engines in history with the 4-71 Detroit Diesel. The first order rocking couple is easily mitigated with counterbalance shafts as has been done since the inception of the 71 series engine in the 1930's. Almost all 4-cylinder engines use counterbalance shafts today so just about any crankshaft configuration is possible now.

 

[GregLocock]

what firing order would a UDLR crank give you? I could work it out but its easier to ask!

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

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[TugboatEng]

On the 2-stroke engines it's the same as the conventional 4 strokes. For the inline-6 we were taught a method: Too young, too old, just right. That's 15, 36, 24

Anyways, the cross-plane 4-cylinder 4-strokes are 1324.

 

[Lapislignum]

Your choice of 4 options (or 8 if you want to fire 4 cylinders on one bank followed by 4 on the other) Greg. Based on GM LS V8s it would be 1 4 3 2 6 5 8 7 but this hits the four front cylinders followed by the 4 rear cylinders, there would probably be a better option, I'll have to look into it.

 

[GregLocock]

Yeah, you don't do that the torsionals are bad.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

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[Lou Scannon]

When discussing firing order on multibank engines better be clear about cylinder numbering... some manufacturers do it differently

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

 

[Lapislignum]

6 post-it-notes later and it's either RRRRLLLL or firing the 4 "front" cylinders followed by 4 "rear" cylinders.

That's good, this idea can live outside my head now.

Regarding cylinder numbering the GM LS convention is cylinder 1 is on the front left corner of the car (front mounted longitudinally oriented) odd cylinders are on the left, evens on the right.

 

[BrianPetersen]

2009+ Yamaha R1 firing order is 1-3-2-4 with intervals 270-180-90-180. The closely-spaced firings (overlapping power strokes) of cylinders 2 and 4 are on opposite sides of the output gear that drives the clutch basket, and that's probably not by accident.