Crankshaft Balancing – Part 1

[Music] hey you're at steve tech i'm steve this is what we're going to be talking about today is how a crankshaft is balanced and so we're going to go through all the steps of how it's balanced why it's balanced and what you're actually accomplishing here and just to give you an idea so you understand what's going on and what's all entailed into it and why sometimes it's going to cost a lot of money to balance crankshaft sometimes it's uh you know it's a the cheaper version sometimes it goes real quick a lot of times it doesn't so anyways let's start over here with what you need to do so our first process is we are always trying uh we're going to balance all of our individual components together now uh in the aftermarket world with connecting rods uh really good high quality pistons high quality connecting rods uh these things they are extremely close together i mean if they're if they're within a gram i don't even touch them that's not even worthwhile to do so what we're going to do is i'm going to show you uh the bob weight so you cannot just throw a crankshaft in here in the machine and spin it without having some form of simulation of what the piston rod and everything weighs so let's go over and start talking about the bob weight so our bob weight consists of what is connected to the crankshaft what is spinning around you know this is going around and what's going up and down that's going up and down all right so our anything that is rotating around is called rotating weight and anything that's going up and down i.e the piston or the small end of the rod is called the reciprocating weight so first thing we're going to do is we go over here to our bob weight number and other machines might have other things to do you can even have a piece of paper similar to this where we can uh you know the piston weight pin weight rings and all the stuff so everything that is right up here on the screen so you're going to enter in all that stuff and so what we want to do first is we're going to do the connecting rod big end so we got zero out our scale yup actually let's put do it this way we're gonna zero out our scale we use this fixture which is allowing us to just weigh the big end of the connecting rod the rod needs to be parallel the small end of the connecting rod is suspended out here everything is on a little roller so it will self itself excuse me it will self-center itself all right but nice and level everything's right there we come in we go okay our connecting rod weight is uh 424 so come up here we'll go 424.6 enter all right now the next weight it wants to know and we'll do this step by step so you're seeing exactly what it's asking us and us and exactly why we're doing this so that's the main part of rotating weight as you can see right here this is a rotating weight anything that is connected directly to the crankshaft and goes in a circular direction rotates next thing it wants to know is your bearing insert bearing inserts our inserts are 40.9 40.9 all right the next thing so it gives you a grand total there it wants to know how many throws or rods per throw so obviously on the v8 we're gonna have two connecting rods per throw four cylinder talk about that in a second obviously you only have one and then uh straight sixes some of those other options would might have a different rod throw configuration now we're just showing you how to do for uh the typical v8 domestic v8 uh there are some crazy rod journal designs uh that are out there but we're not gonna be covering those right now all right so it's asking it gives you how many throws per cylinder so it's just timesing those two so your big end of the rod the bearing times two because we got two rod throws or two uh connecting rods on each throw gives you a total and then it even wants to ask you what the oil weight is because yes there's oil weight that is in there so typically we're going to be in between three and five most of all time we're just using five for that number so that's actually the oil that is inside the connecting rod journal from center of the crankshaft out to the connecting rod journal and oil that thin you know two thousands two and a half thousand three thousands of oil film that is right there all right so that gives us our rotating weight all right now we're gonna start figuring out our reciprocating weight so our reciprocating weight first thing we're going to look at is this connecting rod small end so small end or pin end if you want to call it that okay so now we do the same thing we're just going to zero out our scale we flip this around and now we're weighing the at this level there we go all right make sure that everything is square in there so it's not giving us any bogus reading [Music] and let's zero this out there we go and we're at 170 7.5 one seven seven point five enter all right now it's going to be asking us for a piston weight so we'll take this off we're already zeroed up there now we have done the complete connecting rod and when you do this correctly you weigh the big end you weigh the small end you can do a total weight on the rod the total weight is 602.3 and we can look on there 424 and 177. we'll add this together on the old calculator uh 177.5 plus 424.6 equals 602.1 602.3 so i'm just off like a decimal place that way we know that we have correctly weighed and had the rod balanced properly if you had the angle real wrong and you had it down like this it actually skews your balance and changes things so that's why we always want to have it nice and level and the quick check is to see yep the thing weighs exactly what both halves weigh together all right now we weigh our piston just the piston all right we're at 520.5 but we'll just change that five two zero point four enter all right now it wants to know what our pin weighs piston pin is 184.2 that's already entered in there now this particular piston has pin buttons so if you're not familiar with pin buttons we'll probably cover stuff like this later in one of the other videos but that goes in there and what it does is it simulates uh provides support for the oil ring and actually pin buttons are actually nicer i kind of like them better than a support rail but they do add a little bit of weight weight is not super critical in this and i'll tell you about that in a second after we get our bobweight number so that's 17.6 is what the pin buttons weigh one on each side so that holds the pin in from going anywhere so the piston pin is in behind there this supports the rail it sits out there nice and flush exactly like that so this is what called it's called a pin button all right then we weigh our rings 51 grams oh these are when we use the pin button that means we don't use a spiral lock or don't use any kind of clip out here so the two ways of doing a spiral lock or a spiral lock with a oil support rail or a pin button those are two methods of supporting that oil rail and holding the piston pin from going back and forth all right so that gives us all of our reciprocating weight that equals 950 grams so our total reciprocating weight is uh 1901. you get that number because that is times what how many pistons and small end of the connecting rod are going up and down right so ironically enough it gives us our total reciprocating weight which is uh 1901 but even though there is two going on they are opposed from each other and one is going up as the other one is coming down so as they are posed from each other you actually divide that number by two which gives us our total reciprocating factor of 950.7 so our 950.7 plus our 936 gives us a grand total of 1886 is our bob weight so that's what's getting simulated there now if we changed our balance factor from 50 to 51 which is a over balance or 49 which is a under balance so if i change this number right here now let's watch your number our bob weight is 1886. if we change this number to 49 for under balance it changes our weight to 1867. if we change it to overbalance to 51 percent changes it to 1905. so see how much we're changing our bob weight these these engines will run at 50 49 48 they'll run at 51 52 very easily and you'll never you literally don't ever know it point blank and there is a little bit of math and there is a little bit of things that like cop eliminator uh pro stock guys winston cup guys will under balance or over balance because in a under balance situation they tend to ex vibrate less they they tend to accelerate better in an overbalance situation they tend to maintain higher rpm better so you're actually not balancing it quote unquote correct because this is the generally accepted sae method 50 so uh as racers we can change and manipulate those bob weights so we're actually making it way less than actually putting it out of balance by giving it over balance or under balance trying to achieve a better accelerating or a better better high rpm deal in general 50 percent is for everything that we do in big horsepower uh big rpm big horsepower stuff is great has no problem okay so we have our bob weight number now we come in and we simulate and build that bob weight so here's what the bob weight looks like without any weight on it so we then say all right this thing needs to be um half oops so it gives us our machine gives us half of a bob weight so we can do one half at a time or you can just do the whole thing at a time so i prefer to just do it the whole thing at a time all right so these are just a little speed nuts make sure gauge starts out at zero scale is zeroed so obviously we're gonna put the same weight on each side so first off we put that on there that's 14 24. that's 1683. 1770 let's i think we'll do it this way 1873 our bob weight number is supposed to be 18.86 [Music] so we'll just do whatever it takes in order to make that weight and do it equally on both sides that's 83 that will be at 86. there you go 1886.9 where it's supposed to be 1886.7 so we're not going to worry about that two-tenths of a gram all right so we're at like i said we're at 1886.9 it's 1886.7 not gonna worry about that because let me show you something here 1886.9 here's this post-it note all right that just changed it almost a gram eight tenths of a gram okay this is eight tenths of a gram it's just a post-it note okay so keep that in mind as we were doing this on what that weight is i mean that's a almost a gram right there

Channel: Engine Builder

Views: 17,196

Rating: 4.8666668 out of 5

Keywords: engine, engines, engine builder, steve morris, steve morris engines, steve tech, balancing, engine balancing, crankshaft, crankshaft balancing, rotating assembly

Id: aNnO1XSByLE

Length: 14min 55sec (895 seconds)

Published: Fri Aug 28 2020