V6's are inherantly more imbalanced that an i6 so I would assume they can be "overbalanced" as well though the article indicates that it's a drag racing technique, in a street/circuit car your going to be crossing the "overbalanced point" more often and thus wear bearings quicker, if I'm reading the article right
What wiki has to say about it: Due to the odd number of cylinders in each bank, V6 designs are inherently unbalanced, regardless of their V-angle. All straight engines with an odd number of cylinders suffer from primary dynamic imbalance, which causes an end-to-end rocking motion. Each cylinder bank in a V6 has an odd number of pistons, so the V6 also suffers from the same problem unless steps are taken to mitigate it. In the horizontally-opposed flat-6 layout the rocking motions of the two straight cylinder banks offset each other, while in the inline-6 layout, the two ends of engine are mirror images of each other and compensate every rocking motion. Concentrating on the first order rocking motion, the V6 can be assumed to consist of two separate straight-3 where counterweights on the crankshaft and a counter rotating balancer shaft compensate the first order rocking motion. At mating, the angle between the banks and the angle between the crankshafts can be varied so that the balancer shafts cancel each other 90° V6 (larger counter weights) and the even firing 60° V6 with 60° flying arms (smaller counter weights. The second order rocking motion can be balanced by a single co-rotating balancer shaft.). This is almost the same technique which balances an even firing 90° crossplane V8 in primary and secondary order. A 90° V8 is in primary balance because each 4-cylinder bank is in primary balance, and the secondary of the two banks can be made to cancel each other using a crossplane. However, there is no equivalent of the crossplane crankshaft for the V6, so that the vibrations from the two banks cannot be made to completely cancel each other. This makes designing a smooth V6 engine a much more complicated problem than the straight-6, flat-6, and V8 layouts. Although the use of offset crankpins, counterweights, and flying arms has reduced the problem to a minor second-order vibration in modern designs, all V6s can benefit from the addition of auxiliary balance shafts to make them completely smooth.[5] When Lancia pioneered the V6 in 1950, they used a 60° angle between the cylinder banks and a six-throw crankshaft to achieve equally spaced firing intervals of 120°. This still has some balance and secondary vibration problems. When Buick designed a 90° V6 based on their 90° V8, they initially used a simpler three-throw crankshaft laid out in the same manner as the V8 with pairs of connecting rods sharing the same crankpin, which resulted in firing intervals alternating between 90° and 150°. This produced a rough-running design which was unacceptable to many customers. Later, Buick and other manufacturers refined the design by using a split-pin crankshaft which achieved a regular 120° firing interval by staggering adjacent crankpins by 15° in opposite directions to eliminate the uneven firing and make the engine reasonably smooth.[6] Some manufacturers such as Buick in later versions of their V6 and Mercedes Benz have taken the 90° design a step further by adding a balancing shaft to offset the primary vibrations and produce an almost fully balanced engine. Some designers have reverted to a 60° angle between cylinder banks, which produces a more compact engine, but have used three-throw crankshafts with flying arms between the crankpins of each throw to achieve even 120° angles between firing intervals. This has the additional advantage that the flying arms can be weighted for balancing purposes.[6] This still leaves an unbalanced primary couple, which is offset by counterweights on the crankshaft and flywheel to leave a small secondary couple, which can be absorbed by carefully designed engine mounts.[7] Six-cylinder designs are also more suitable for larger displacement engines than four-cylinder ones because power strokes of pistons overlap. In a four-cylinder engine, only one piston is on a power stroke at any given time. Each piston comes to a complete stop and reverses direction before the next one starts its power stroke, which results in a gap between power strokes and noticeable vibrations. In a six-cylinder engine (other than odd-firing V6s), the next piston starts its power stroke 60° before the previous one finishes, which results in smoother delivery of power to the flywheel. In addition, because inertial forces are proportional to piston displacement, high-speed six-cylinder engines will suffer less stress and vibration per piston than an equal displacement engine with fewer cylinders. So yeah maybe they can be "overbalanced" I don't think I will be doing that though.
There are small variations in the weights of conrods/pistons By weighing all 6 (in the case of a v6 engine) you'll end up with one thats slightly less in weight than the others and one thats the heaviest. The lightest one sets the mark for the others...... which will have the conrod endcap ground off till all 6 pistons weigh exactly the same weight. the pistons are now "balanced" This then changes the effect on the crank........ so the crank must be re-balanced to suit the new pistons The flywheel and clutch are part of the cranks "spinning forces" so they are also required to be balanced so it all matches up. Usually this is done by drilling out material from the crank, flywheel, and pressureplate to acheive the correct balance...... Some 'balancers' cut corners by spot welding on a small counter weight to the pressureplate.... not good as the weight can and often does come off under high revs. The term "blueprinting" is related to the lengths of the pistons AND conrods.... Because of mass production the machining of these parts can and does vary considerably. Imagine you get the first piston and last piston from a mill run of 10,000...... the wear in the cutting tip alone can see a huge differance let alone other contributing factors.... Blueprinting see's ALL the pistons the exact same length and with the exact same gud/pin hole.... same applies to the rods..... all exactly the same length, not +/- a few thou as we see in std motors Blueprinting is pharkin expensive and time consuming....... :bash: Quick example: ( my race bikes engine ) std rpm limit = 9500rpm with balance job = 10,800rpm balanced and blueprinted = 14,000rpm .... cost ....... dont ask. Kingy
Oks... So reading that article that was poset up by Wayne. Why would you bother with getting the pulley and fly & clutch balanced with the rest of it for? From what I can tell it wouldn't really matter as the pulley is just a spinny roundy round thing (technical term ) with a constant cross sectional area as is the fly so is shouldn't really be a issue at all.
Rod and piston assemblies aren't just balanced by removing material from the rod cap. Rods are weighed at both the small and big-ends, lowest number counts. All small ends are matched, all big-ends are matched. Pistons are weighed and material taken from beneath the pin at the pin boss. They are then reassembled and checked for total weight,if they are the same, then a "bob" weight is put together to go on the con-rod journals of the crank. The crank will either have material removed or heavy metal slugs added. Balancing the damper and fly is done because although being a machined peice, the density of the material is not uniform all over, they can be balanced individually or together with the crank/bobs, preference is to do the lot as an assembly as that is how it will be working. Having them bolted to the crank also changes the harmonics due to greater mass.
The internals of my build were done that way. Every same part was altered to spec. I forgot the name of the material they used to add the weight though :/ It was a pretty expensive process from memory lol I had all of mine balanced together as well.
