# Talk:Balance shaft

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Some more hepl visualising second order vibrations would be handy. Even after looking at the diagrams, I still can't see how this force arises, and considering I'm a second year engineering student, I really should be able to.

The 'here' link to an animation appears to be dead -1st paragraph

to visualize the assymetry of a piston (compared to the sinusoidal motion with an infinitely long conrod) imagine the mathematically limiting (but physically impossible) case of the rod being the same length as the crank radius: for 180 degrees the piston moves at 2sin theta (crank = rod is the only situation you get a nice simple relation), and then for 180 degrees the piston is completely stationary. the general case is that in the lower half of travel, the piston moves down overly quickly and is then rather slow about entering and leaving the BDC position. with a pair of pistons 180 degrees out of phase, the upward motion (and hence acceleration) of one is not matched by the downward motion of the other, and this occurs twice per revolution (each piston has a turn travelling up); hence vibration is second order (2*f) — Preceding unsigned comment added by 110.175.57.184 (talk) 03:14, 28 July 2011 (UTC)

## 60 degree v6

The 60 degree v6 is not ideal for 6 cylinder balance, 120 degrees is.To
explain simply: 90 degrees to a v8 is ideal, the math is 720/8.
the flat four (boxer)is ideal,the math is 720/4. The 72 degree v10 is ideal,
the math is 720/10. The 60 degree v12 is ideal, the math is 720/12. The
engines to "play" with are less than 4 cylinders, and even then you can get
close to ideal balance, never correct.If the fire between cylinders is more than
180 degrees(less cylinders than four), the balance is man-made and flawed,
never ideal.
Bgd73 22:26, 1 May 2006 (UTC)

i don't think either of these is true. i'm pretty sure the best balance that can be had with a V6 is 90 degrees plus a fully counterweighted crankshaft. also, since most of this article is well written and accurate (a rarity in discussions of engine balance) i'm pretty confident the section on V6's has been added by a second author. for one thing, it perpetuates the myth of the "three 90 degree lobes" crankshaft on 90 degree V6's. because the original buick V6 block is a shortened version of the V8, people have leapt to the conclusion that they also hacked off one quarter of the crankshaft. this is complete BS - the crank has three journals with 120 degree symmetry. the "roughness" associated with this engine is the necessary uneven firing interval of three journals driving 90 degree cylinders, rather than mechanical imbalance. later complexities such as split pin crankshafts are to even out the firing intervals. i'm also pretty confident Bgd73 wouldn't know a phasor diagram if it bit him. the math involved is not simple. in fact, it's very hard to find basic information on the internet for this topic. the relevant textbook is http://www.amazon.com/Reciprocating-Machinery-Dynamics-Mechanical-Engineering/dp/0824705319/ref=sr_1_1?ie=UTF8&qid=1311821425&sr=8-1 — Preceding unsigned comment added by 110.175.57.184 (talk) 02:56, 28 July 2011 (UTC)
ok, i see what Bgd73 has done. Bgd makes the common mistake of assuming that balance means even firing intervals. balance means reciprocating components cancel each other in a way that the engine doesn't vibrate, and is fiendishly complicated. even firing intervals is the simple topic of having identical time between detonation, and he is even incorrect in that regard ... his calculations produce the angle between crank pins in an inline engine, not an optimum vee angle. the "harshness" of uneven or infrequent firing intervals is perceptible mainly as a weird exhaust note, but wikipedia entries are littered with the contributions of people who have "realised" that smooth engines have frequent regular firing intervals, and think they understand balance. there are probably dozens of articles where balance is discussed, and none of those sections are fully reliable because it's one of those unfortunate topics where people who don't understand the topic feel qualified to make contributions. the only less reliable topics i know of is where people feel compelled to explain religious history as they were taught in sunday school. this article is brilliant (currently) up to the v6 section. i'm not familiar with v6 balance shafts so the best improvement i could make would be to delete that section. hopefully the original author or someone with a degree in mechanical engineering could do a rewrite