Talk:Crossplane

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Added 3d render of crankshaft; removed reqdiagram Egmason (talk) 08:26, 18 May 2010 (UTC)
This is not representative of of a cross plane crankshaft in an S4 or V8. Typically, an inline four with a 90-crank uses two pairs of opposed big ends at 90º to each other. That is 0º, 180º, 270º, 90º. It's like two Triumph engines at 90º to each other. The YZF R1 which is mentioned in the text uses 0º, 90º, 270º, 180º - an opposed pair in the centre but firing like a pair of Ducati twins. Sir smellybeard (talk) 17:11, 4 December 2012 (UTC)

Porsche Flat 8[edit]

No mention is made of the Porsche 908 Flat 8 engine. Later variants of this used a crossplane crank to gain the same effect as a flat crank V-8.Sir smellybeard (talk) 17:19, 4 December 2012 (UTC)

The original flat-8s, the 1.5 litre F1 and the derivative 2.2 litre sports car engine (type 771), were effectively boxer fours end-to-end, offset by 90°, and using a firing order (assuming the usual "German" cylinder numbering of down one bank, then the next) of 1,7,2,8,5,3,6,4. When the 908 came in with its requirement of a bigger 3-litre motor, Porsche decided to make changes to the crank to allow for simpler exhaust manifolds like those on V8s. They first tried a firing order of 1,8,2,6,4,5,3,7 - this is like a flatplane crank with 90° "split pins" (probably actually more like a boxer crank with a 90° offset instead of 180°, so kind-of half-cross-plane). Due to engine ancillary failures, they tried 1,5,2,7,4,8,3,6 which used the same crank - cylinders 6 & 7 and 5 & 8 simply being swapped in the order.
This still resulted in failures, probably because of the large primary free force in the horizontal direction, due to the crank configuration, shaking things about. After this they went back to the 771-like order, as evidenced by the exhaust manifold cross-overs on later 908s needed to sidestep the uneven firing in each bank. (I forget where I first read all of this, but I've just come across much of the same information - i.e. firing orders and reasoning - in: Porsche 908: the long distance runner by Neßhöver, Roybach and Schwarz, pp. 192 - via Google Books)
That crank effectively inherits the smoothness / balance of the boxer-four (itself from the boxer twin). It is, I suppose, "crossplane", but as a boxer with 180° throw pairs instead of shared journals, 9 main bearings instead of 5 and in an unusual configuration i.e. 0,180,90,270 instead of 0,90,270,180 - of course the opposite bank has opposite crank angles: 180,0,270,90, so it's a kind of double-cross-plane crank.
A straight-up crossplane crank, with shared journals like those in V8s, fitted to a flat-8 would need simultaneous ignitions (2 cylinders at a time), would be uneven firing and would have a rocking couple without the convenience of the 90° bank angle for easy balancing.
If we're continuing down this route, there's also the straight-8s to consider (three types of crank commonly used, all potentially "cross-plane") and other, more interesting things like V16s, flat-16s and H16s etc. At that point it becomes more a description of engine balancing in general than it does of this one particular crankshaft configuration, because the same considerations apply to all engines.
For example, the "process" between the crossplane straight-4 and the crossplane V8 is the same as that between the inline 5 and the 90° V10 (or the single and the 90° V-Twin, ultimately). The only differences being that inline 5s are more common (in automotive use) than crossplane fours and generally use the configuration that minimises the primary rocking couple, whilst the 90° V10 takes the one with maximum primary rocking couple (because of the easy balancing afforded by the bank angle). The analogy would hold if cross-plane fours normally had a crank config. of 0,180,90,270 (like one bank of a type 771).
Identiti crisis (talk) 01:34, 11 May 2013 (UTC)

Poorly written[edit]

I think this is poorly written since the article starts out saying crossplane crankshafts are a feature of V8 engines, and then mentions their use in inline 4 and V twins. If I remember to and nobody objects I'll take a crack at editing it. Nasch (talk) 19:32, 2 April 2013 (UTC)

It's not great, but the V8 / I4 issue isn't a problem. It's a common situation for any sort of "encyclopedic article" context that <topic> is commonly and almost entirely used in one context, but it is also used in some other context as well. It's still appropriate to write an article that focuses on the major use first, then introduces the narrower one. Even if this makes for an article that is 'strictly' logically self-inconsistent, this isn't a problem. Clarity in writing is more important than logical formalism, because we're writing for a human audience that appreciates clarity but understands the Godelian problem that attempting strict literal consistency often damages readability for more seriously. Andy Dingley (talk) 20:34, 2 April 2013 (UTC)
I'd say it is a problem when a statement is wrong. "The crossplane or cross-plane is a crankshaft design for V8 engines with a 90° angle between the cylinder banks." is a wrong statement as crossplane crank can be used on L2, L4, L8, L16, V2, V4, V16, flat4, flat8, flat16 or even on a 120 degree V8 (of course a 90 degree crank in a 120 degree V8 results in uneven firing spacing, but so did many 90 degree V6s). A crossplane crank is a crank with its crank throws at 90 degree angle, no matter what the number of cylinders or V bank angle may be. The article should start from that simple definition and then go into particulars. Alfa Romeo P3 inline 8 cylinder (L8) had two flatplane 4 cylinder cranks (up down down up) connected in the middle at 90 degree angle. Bugatti T35 (L8) crank had up down up down left right left right throws. Both of these cranks are crossplane cranks because the throws had 90 degree angle. Nasch, please rewrite it. Give me a message if you need help. Yiba (talk) 17:36, 23 July 2013 (UTC)