Engine Building Part 2 - How to Choose a Crankshaft

[Music] hi everyone thanks for stopping by peace garage now we're going to talk about choosing a crankshaft and this is not a very difficult decision although some people do spend more time choosing a crankshaft than they do a spouse but that's a totally different story all right before we get into the detail i'm going to give you a cheat sheet for choosing a crankshaft at the beginning of the video first you want a cast forged or billet crank and is it made out of forged or billet material stroke length main journal diameter rod journal diameter

fillet radius number of counterweights method of heat treating the crank snout size what kind of windage treatment does it have are there any lightning holes what's the crankshaft weight the rear main seal type crank flange type journal surface type is it balanced what other material properties is it a twisted or non-twisted forging massive inertia or the mass moment snout key way and finally damper required when you're choosing a crankshaft there are a lot of things to consider but let's try and keep it as simple and easy as possible so you know you're choosing the right

one first what do you do with it is this a car you're going to drive around beat on a little bit occasionally and and take it to cruise nights is this something you might race a few times a year or is this a hardcore race car and then are you gonna have a circle track racing car drag car top fuel drag car whatever but for the majority of the people watching this video you're looking for performance engine and let's call performance engine anything over 500 horsepower 500 let's call 500 to a thousand and when you're

choosing a crankshaft you're going to be able to choose from three basic types and this is the bulk of your decision making process is how it's made and your choices are it's either going to be cast forged or billet the difference in these three is simply in the way they are made for a cast crank a mold is made and the molten crank material usually iron is simply poured into the mold creating the casting cast cranks are very easy to produce or mass produced so they're very common in oem applications now the cast crank is

going to be made out of either iron or a nodular iron the tonsil strength of a common cast crank is going to be about 65 000 80 000 psi which is relatively brittle but it's perfectly suitable for a general automotive use an oem nodular crank will have a tensile strength above 100 000 psi which gives it better ductility and an elongation rating of about three percent and this is suitable for truck applications and higher performance oem engines the deflection rating refers to how much a crankshaft can be deformed before it fails now forged cranks are

going to come in two basic types twisted and non-twisted the twisted crank is made during the manufacturing process where the piece of metal that's going to turn into a crank is heated up and that piece of metals it'll literally twist it into position meaning the throws the rod rod and the counterweights are all twisted into position while it's hot this is the cheapest method of forging a crank so that'll be the most common the non-twisted forging is where the material is heated up and it is forced into position without twisting the crank that's a little

bit more expensive however the twisted crank being the most common really is going to be strong enough for most applications now a forged crank can be made out of a variety of steel alloys from 1053 1045 mild carbon steel to all different kinds of alloys which we're going to talk to talk about in a second but it's that wide variety of alloys that can go into a forage crank or be used to make a forged crank that allow you to choose a wider range of applications not only that the forged crank is going to be

stronger and since it's uh let's say not it's not as common as a cash crank it's gonna be more expensive but as an alternative to buying a super expensive billet crank the forged crank is gonna be very reasonable and it's gonna give you the strength you need next we talk about the billet crank billet cranks are cnc machined from a solid chunk of high strength billet steel alloy they are typically the strongest and stiffest available and are the overwhelming choice for unlimited applications such as top field dragsters pro stock pro modified and drag racers now

the billet crank since this machine out of a solid block of material the real benefit of the billet crank is that it can be machined in an almost unlimited amount of configurations whether you're trying to maintain or obtain a large amount of stroke or certain offset or you want the the counterweights machined a certain way to reduce windage or friction whatever billet cranks offer that kind of flexibility however they are by far the most expensive so regardless of whether you choose a cast forged or billet crank the quality of the end up product really lies

in the heat treating when is finished being machined how is it heat treated before the mains and the pins for the pistons how is it polished and how is it cleaned up the heat treating is what determines the strength so when choosing a crankshaft there are a wide variety of materials the crankshaft can be made of so let's look at them one at a time and see which might be best for your application a regular cast iron crankshaft is going to have a tensile strength of roughly 70 80 000 psi very common in oem engines

also the nodular iron a little bit more refined a little more carbon in there and gets the tensile strength up to 95 000 also common in some higher performance oem engines a cast steels crank now we're getting into the when you say i have a steel crank in my engine it'll be a cast steel crank it can be have a tensile strength of up to 105 000 psi and this is really the strongest casting of all the castings that are available now we get into the uh alloys or the combination of materials and forgings there's

10 10 10 45 10 53 these are going to get you in the 100 000 to 110 000 psi range these are the more high carbon oem forgings and now we're getting more to the uh cranks or the materials where you have higher performance engines there's a 5140 alloy which is 115 000 psi more for sportsman racing the 4140 gets up to 120 000 psi and it's that's really the premium forging alloy that's one i use a lot and i use the 4340 alloy which is good from 140 145 i'm sorry 140 to 145 000

psi that is the best performance alloy so i choose 4340 cranks when i'm building anything that's going to be 500 to 1000 horsepower then we get up to the uh billet materials that are available for billet crankshafts first we have something like an en-30b that's going to get 160 000 to 165 000 psi it's a premium billet then we get to the 43 uh 4330m that's 165 000 that's the maximum strength oil alloy along with the 300 m 106 165 000 also maximum strength alloys so along with choosing whether the crankshaft is cast forged or

machined out of a billet there's also a variety of materials within that you can get a steel forged crank that's very strong and plenty good enough for your engine up to 500 horsepower and it's going to save you money rather than stepping over into a 4140 or 4340 alloy steel forging so there's a there's a range there within the casting the forging let's forget about billet because no one's gonna be spending six thousand dollars for a crankshaft and the regular uh let's say casting for a uh a cash crank you're looking at oem cranks that

are gonna be like the in the two to let's say 400 range and then we start to get into the forged materials ranging from like 400 to 800 900 depending on the complexity or the alloy used to make the crank so now we talked about the types of cranks that you can buy cast forge billet we talked about the twisted non-twisted for the forged crank the billet crank the flexibility of the cnc machining and heat treating i briefly touched on that but here's something really to consider where is the crankshaft made where does the bait

where does the material come from what mill where is the steel mill that made the material that goes into the crankshaft that makes a huge difference i've recently got involved with uh some material issues with a part and i had two parts one was made by material made from one mil the identical part was made with material made by a different mill and the material made by one mil even though they're both made to a specification an astm spec or a mil spec whatever you're gonna whatever it's determined that needs to be made to spec

the material made at one mill was not as let's say defect free as one from another mill it's just like a hamburger or any other food you buy you can go to one place and get a high quality steak or you can go to another place and get a lower quality steak you can buy a rib eye at one place in a row everybody another place they don't taste the same that's exactly what happens with materials for crankshafts i i strongly suggest that you look at and find out where the crankshaft is made because crankshafts

from china can be very attractive you can for example if you wanted to buy a forged 4340 crankshaft and you have two crankshafts one of them is made in the usa one of them is made in china and you're thinking hey they're both 4340 forged crankshaft the american-made one is 850 and the chinese one is 650. even though they're made out of the same material grade they're not identical there are ways to um let's say adjust the smelting process which is how they take them the steel how they melt it and how they put the

ingredients in and how they clean off the slag and how they purify the material before they pour it into the billet that's used for the forging and that can make a huge difference there's um there's something in the material called inclusions you can have inclusions or porosity an inclusion is where you have a small defect in the material meaning that while the material is being made there's extra silicon in there there could be extra carbon nickel something in there and as the billet is made you have this very small it can be uh maybe one

thousand couple thousands big and is going to be in the material and that is going to weaken the crankshaft overall versus another mill that has a higher purity rating when they make the material or smelt the steel so the if it's inclusion free it doesn't have any foreign material in it or voids which are small air pockets uh something like that the better quality of the steel the better quality of the crankshaft so a 4340 crankshaft made in one place versus a 4340 made in another place are not going to be identical and if you're

going to be building a high dollar engine you're putting your time your energy and your money into building something looking and buying something cheap because it's it's the same number but it's cheaper because it's made in china i really strongly suggest you take a look at that because i've heard too many results where uh crankshafts have broken and it was a cheaper chinese crank or an offshore crank that wasn't really made to the same specifications as a mill that might be in the united states or uh i shouldn't just say united states a mill that

produces a quality steel versus a mill that's pumping out cheap and they really don't keep track of the quality of the steel that they're making so now after the crankshaft is made it has to be heat treated and the heat treating process is critical to the finished product and what you ultimately buy and how long it's going to last there are some heat treating basics that we're going to go over real quickly and depending on the crankshaft you buy you may or may not be able to find out how it was heat treated but in

case you do this is what you need to understand after our crank is roughly machined it's baked to roughly over a thousand degrees f then it's rapidly cooled or quenched in water oil or sometime to some type of polymer quenching now the crank is stronger but it has little ductility or impact resistance so it has to be relieved the stress have to be relieved or it has to be tempered and that involves heating the crank again to a temperature roughly around six or seven hundred degrees f then the cooling process is controlled and according to

the properties of steel the cooling process will determine the final outcome of that heat treat the final step after all the machining is hardening of the journals usually with a process called nitriding and nitriding is something we can get into here but but basically it involves heating the crankshaft and in a closed chamber oven introducing ammonia nitrogen gas and that reacts with the carbon on the surface of the metal and it hardens approximately ten thousands of an inch deep now when you're choosing a crankshaft you won't necessarily have the ability to select the heat treating

process involved but it's good to know what the heat treating processes are so if it is indicated in any of the specifications you have a good idea of how it was made this is why it's important to understand the heat treating process the crankshaft went through when it was being manufactured and it all has to do with machining when you go to put it in now if you're just rebuilding an engine you're thinking should i replace my crankshaft here's something to consider if you have a factory cast crank that crankshaft can be re-machined let's say

you spun a bearing and you have a big groove and you need to recut the main bearing uh main journal because you have a gouge a cast crank regular from the factory that can be re-ground you can cut that groove out of there and reuse that crankshaft without jeopardizing the integrity of the heat treat now once you get up to a forging most oem forged cranks are induction hardened induction hardening is when they take an electrode put it around the journal and electricity is passed through which heats up that journal very very hot and it

creates a heat treat that goes fairly deep so on a factory steel factory forged factory cast crank you can have those re-machined and re-cut without really worrying about it however if you buy a billet crank and it was either not nitride heat-treated or tough triding which is another kind of heat treating you're only going to have ten thousandths of an inch deep of heat treating and if you have to cut something because you spun a bearing or you let's say you have a block that you really want to use because it's it's the same here

as your car and you're choosing a crankshaft to fit in that block however something happened and the main uh main bearings or the main journals they had to be re-machined the cap and the block which means you need an oversized or undersized bearing or something happened and you need to re-machine the crank to fit in there if you use a forged crank that was simply nitride heat treated and you have to cut it and let's say you cut five thousands off you only have five thousands left of heat treating which is not very much so

understanding your heat treating is going to help you choose which crank to use when you're either rebuilding or building a new engine using an old block get those uh heat treating things straight in your mind and keep it in the back your mind as you're choosing do i want for do i want the cast crank cast steel cast nodular iron it's going to fit my horsepower or is it going to be forged i want a forged crank because it's stronger the fillets in between the uh with counterweights and the pins and the mains are you're

going to bigger fill it so it's going to be stronger but it was nitride heat treated meaning that the heat treating is only so deep enough to machine it i might have to have it re-heat-treated after it's machined or you go with a billet crank and you gonna be heat-treated to the point where it doesn't matter it's custom-made anyway that's why knowing what kind of heat treating was used is important so aside from understanding those basics there are some more advanced options you may or may not have depending on the manufacture of the crank one

of those is the design of the counterweight now the counterweight can be made and the two separating factors here are it can be either made for ease of balancing or it can be made for e for the loading on the main bearing the counterweight ideally should be 180 degrees off from the pin you have a counterweight here and a piston here you that ideally should be 180 degrees across and that can vary depending on the manufacturer you may or may not have an option on that but the counterweight that you choose does play a role

when it goes when you get to the point where you have to balance the crankshaft those counterweights can also be designed to reduce weight and windage now another option you may have depending on the manufacture of the crankshaft is the drilling of the crank pin the purpose of drilling a crank pin is to reduce the overall reciprocating weight of the engine so if you're looking for a higher rpm engine or you want to produce more rpms the easiest way to get there is to reduce the reciprocating weight of the crankshaft and the whole rotating assembly

and one way to do that is to drill out the pin now when you do that you're not really jeopardizing the crank the strength of the crankshaft because in a forged crankshaft with uh like a 4340 forged crankshaft it's going to have very very strong ductility it's going to be really strong and can have elongation when we talked about elongation the elongation rating on a 4340 forged crankshaft can be up to 20 22 percent maybe 23 so that crankshaft can deform a lot more before it fails and a way to reduce the amount of elongation

and reduce stress on the mains is to reduce the reciprocating weight and the drilled main pin is one way to do it another thing you may hear about or have a choice with when purchasing your crankshaft are gun drilled mains now that is done just simply to reduce the weight of the crankshaft overall it can affect the performance because the piston and the crankshaft acts as a shock absorber and as you gun drill the mains [Music] you're you're kind of i don't want to say weakening but you're reducing the amount that the energy that that

crankshaft can absorb so if you're concerned about uh the yielding of the crankshaft then don't worry about the gun drilled mains now we can talk about the strengthening of the crankshaft we talked about the strengthening through heat treating we can have induction hardening nitriding tough triding those are all methods of hardening the crankshaft and creating the the hard layer and how deep it will go the other thing that has come up recently and uh kind of a matter of controversy i think is the use of cryogenics a cryogenic treatment to a crankshaft is when they

take the crankshaft and submerse it into something that's going to cool it to minus 300 degrees fahrenheit and the thought process here is to freeze the crankshaft and by freezing it it helps release the stress when it's taken out and put into room temperature let's say 70 degrees fahrenheit and it's allowed to slowly warm up to that temperature all of the grain structure and all the stresses in the crankshaft can be relieved through that process previously i'm going to say maybe 10 years or more ago this was thought more to be of a snake oil

kind of thing where it really doesn't do anything but recently the techniques and technology around submersing the crankshaft and something to freeze it holding it there from 24 to 36 hours and then controlling the temperature as it comes up to 70 degrees have proven to have some small gains so some some real high-end engine builders will use this process just to get that little extra bit of strength out of the crankshaft but for the 90 let's say 99 percent of us who are just rebuilding an engine or building one for the first time there is

not a huge benefit in paying for that kind of treatment some additional things many years ago there was a concept of cross-drilled veins where the lubrication hole in the crankshaft was drilled straight through so you have a cross-drilled main shaft for oil this was thought that well if i have two holes to get more lubrication in the crankshaft through the main but what we soon found out what razor soon found out is that when the oil gets in the crankshaft and it's inside where it should be lubricating as the crankshaft spins the centrifugal force forces

the oil out a lot faster and sometimes the oil pump can keep up which could end up starving the bearings so while the cross-drilled main is not necessarily a good idea smaller holes on the pins or the rod journal are a good idea because that can boost high pressure so when you are choosing the crankshaft look at those dimensions those holes and how the oil is going to go through the crankshaft to lubricate your engine you also want to make sure that the oil hole where the oil comes out into the rod bearing and main

bearing have an adequate chamfer on it if you do not have an adequate chamfer on there there's a possibility that the hole could shave the bearing completely ruining your engine most engines or most crankshafts come with proper chamfers on the holes but take a look at it take a look at what they say about chamfered holes look at the picture and make sure it's there it's really critical to have your engine last a long time another thing to consider is is the crankshaft balanced when you buy it does it come balanced if it does not

come balanced i would suggest suggest having it balanced along with the entire rotating and reciprocating assembly if you think about it the crankshaft is rotating this way which is your rotational energy so it's got to be balanced this way to prevent vibration the pistons are well this is rotating this way the pistons are going this way which is the reciprocating weight so when you're choosing your crankshaft you want to see is it balanced if it's not you're going to have to take it somewhere and have it balanced unless you want to purchase a vibration damper

a damper or or a torsional rotational balancer that's going to take care of the vibration of an unbalanced crankshaft but if you can get a balanced crankshaft and even if you do buy a balanced crankshaft i like to take the crankshaft and check it take it to a machine shop say hey check my crankshaft and while you're doing that i'm going to take the rods then the pistons with me with the pins the entire rotating assembly i want the crankshaft balance for rotation and i want all of my rods pistons and the reciprocating assembly balanced

so that the entire assembly is going to be vibration free which will not only add horsepower because vibration is a huge uh theft of horsepower anytime you have vibration that's that's horsepower going bye-bye the more you can balance it the more precise you can balance it the more horsepower you're going to generate and the longer the engine is going to wear because the less stress you're going to be putting on all your main bearings and rod bearings and the less the piston is going to be tilting inside of the cylinder the rings are going to

ride square there's all kinds of geometry involved there but and i know that's beyond choosing your crankshaft but the main point here is balancing buy it balanced and even if it's balanced just have it checked doesn't cost that much it'll give you great peace of mind so like i said at the beginning most people spend more time choosing a crankshaft than they do a spouse or a partner in the end it all boils down to the crankshaft for the application is it going to handle the application that you're putting it in it and that is

the weight of the crankshaft is is it heavy is it going to handle what you wanted to do the strength of the crankshaft what is it made out of is the material going to be strong enough to support your application and are you choosing it from a place that has material that's manufactured smelted melted made whatever you want the mill is making material that's of a good quality which is also important and then the application you're putting in the strength and is it going to perform the way you want it and finally buying a crankshaft

making sure you can purchase mating parts if you have a block if you buy a block and the mains are drilled to a certain diameter which require a certain size bearing and you say i want to use this crankshaft because i like it uh if you can put if you can't find a bearing to match the crankshaft to the block then you're not working together you're not you're not making the the you're not making a good decision there so it's critical to work with the manufacturers uh the the oems all the manufacturers it doesn't matter

what brand you use a scad rpm all the crank brands that are out there dart block whatever you're going to choose they all have really improved their technical support people so if you call up a block manufacturer or crank manufacturer and call their customer service and or tech support and say hey look i want to buy this crank and i'm planning on using it in this block are there any issues they're going to help you because they want to sell their crankshaft so work with the oems work with the tech services department make sure you're

choosing the right crankshaft for your application and when you're done you will have many many years of use and you'll be really happy uh driving the car that's all i can say if there's any questions leave them below we'll try and get them answered i know this is a complex topic and and there can be a lot more going into it but my goal is not to tell you everything you need to know about crankshafts everything about metallurgy and processing but to give you a general idea how how you can set some basic information or

obtain some basic information to help you choose the right crankshaft for your application thanks for stopping by pete's garage [Music]