I have been very fortunate to have a very good machinest as a friend and he has a reputation for building race motors all over the world. When I built my first V8 he sat me down and we talked about balancing. His main point was how much time did I want to pay for and what was I going to do with the motor.....................his usually street balance back in the day was $150 and his race balance was much more depending on the application....................and he was turning people away Balancing is done by experience, smoke and mirrors, good machinery, mathimatical equations, and trying new ideas...................now with that said there are some very basic assumptions, balancing has very little to do with gravity which means something that weighs 5lbs at sea level is going to weigh less at 5000', although it is very small, it still changes. One ounce is 28.4 grams and grams are not effected by gravity...............a rod that weighs 644 grams at sea level will still be 644 grams at 20,000'............just a law of physics. If your engine has an imbalance of 1 oz. at 6000RPM that is like having a force of 40lbs trying to tear the crankshaft out of your motor. Again the laws of physics tell us that centrifugal force multiplies 4X with RPM. It is always more preferable to take weight off of a crank than add it, and you never add weight perpendicular to the centerline of the crank, but always parallel!!!! There are two types of weights invloved in balancing a motor, rotating and reciprocating. The rotating weight is doubled and the reciprocating weight is divided by 2.........or 50%. A Rod is weighed 50% at a time, the bottom rotates with the crank and top is only going up and down with the piston or reciprocating. And when you are balancing a motor you have to add weight for the oil, I know that sounds funny, but oil does add to the weight of the rod both in rotation and reciprocating......................I can't remember the oil viscosity, maybe 20/50w, but only 4/5 drops is about 1 gram..............and there is oil between the bearings, on the crank, on the rods..................etc. Because of the design of V8 no matter how well it is balanced you will always have some vibration.................this gets into over balancing and other things which I just don't know enough to start discussing them. My friend has told me that overbalance is used in some of his race motors that operate at a constant RPM for long periods of time and that using this method does have its draw backs..................... Talking about taking weight off of cranks, surprising as it may seem a lot a race motor builders do not like to drill holes in crankshaft counter weights because they claim it creates an oil windage issue(and can cause imbalance from oil collecting in one or more locations on the crank), and that on most NASCAR/Circle Track and motors that are used at constant RPM levels above 6000RPM, when they take weight off the crank they put the crank in a lathe and remove material without putting holes in the crank. These are just some of the things that have stuck with me over the years, so that when I go to a shop to have motor balanced........these are some of the questions I ask to try and qualify a good machinest from a ??????????????? IMHO
Olerodder - that is a very good read! There is a minor mistake that I am compelled to correct. The reason grams are used in balancing is because the are used in reference to Mass - not weight. If you are using grams to weigh somthing its weight (in grams) will change with the distance from the center of the earth - only its mass doesn't change. Grams are used as both a measure of mass and weight - so you have to be careful of the context. In balancing the mass is measured in inch grams or the number of grams at one inch from the crank center that would be required to equal the force. The number of "inch grams" that are acceptable to the machinist will vary with the speed of rotation and personal experience. If you use a scraper (as I do even on my street engines) then windage becomes a positive function eliminating oil from the crank as well as reducing the amount of windage in play.
PaulS, You are absolutely correct, my fingers sometimes are faster than the Ole gray matter. Thanks for correcting my mistake.
