How to measure a crankshaft, why and other tips!

How do you measure a crankshaft and why do you do it? You guys asked for it, so here it goes. The first thing we need to know is that humidity is bad for engine components, whether it's moisture, humidity in the air. It's a kind of a stormy day today, but it didn't cause all of this. This happened over a period of time, but to prevent corrosion like this, if you are measuring your crankshaft, it means you took it out of the engine. And if it's sitting out of the engine, that means that it can start forming corrosion pretty quickly. So rule number one, Coat the crankshaft, right. Make sure that camshafts, crankshafts, engine cylinders have the light coating of any lubricant, oil, ATF, a lot of different things people use, but don't just leave them out there dry. This is an extreme example, but corrosion can form very quickly. All right, so keep them clean. So when we are measuring the crankshaft itself, some of the key things I want to look at before I actually pick up my tool and start measuring is the visual inspection part. Because if this crankshaft is cracked or has damaged the sealing surfaces, then measuring is going to be the last thing on our mind, right? So one of the key things I want to take a look at are the sealing surfaces. Right here, right behind this gear, You've got a sealing surface and down at the very bottom of the crankshaft you have a sealing surface that the rear main seal goes around. Those sealing surfaces need to be free of imperfections, scratches, anything that can cause fluid to leak through that seal. So take a very good close look at those sealing surfaces looking for any imperfections. Number two, we want to know if our crankshaft is cracked or not. So if you're a professional engine builder getting paid to do this stuff and you have a machine shop or you take it to a machine shop and have some magnetic resonance imaging and other procedures done to a crank to see if it's got any cracks that you can't physically see, but if you're doing a DIY budget build on your own, then maybe a quick test is what I call the Dean test where you take an extension or a piece of metal and you do the ding test. I'll use the end of this micrometer, and now listen to this. High-pitched ding, that's what you want to hear. If I push it really hard against this table, it sounds a little duller. So if you don't hear high-pitched ding like that, then it's potentially got some cracks in it. It's not a 100% foolproof test, but it's a way to kind of get a general idea. Do I have an okay crank, or do I not? So, you know, take it for what it is, right? All right, so measurements. Measurements are going to include things like the mains and the connecting rods. So as a refresher, if you look down the center line of this crank, down through the center, you've got all the ones like this one and this one and this one up here that all line up with each other. Those are indicative of your mains. They're in a straight line along the crankshaft. These are the ones that hold the crankshaft in the block. And they're the ones that the main caps or a bed plate or something is going to go on the bottom to seal it up in there, right? Then if you look on the outside, you got these guys, these guys, these guys, the ones that are to the outside of the center line, those are your connecting rod journals. And the connecting rod journals, for those of you watching this because you're just learning about engines. The connecting rods are what attaches basically your piston to your crankshaft. So your connecting rod is held onto the piston at the top end by a wrist pin. And then down at the bottom, you have where it goes around the connecting rod journals and a cap goes on to secure it in place. And that is how we take our linear motion of our piston and have this guy be converting it into rotary energy, right? Which we need to rotate wheels, right? All right? That's kind of what we're looking at. Now, the two things that are really critical on crankshaft journals are going to be out of round and taper. Out of round is going to tell us if this thing wore unevenly around the diameter of it, right? And then the other one is taper, and that's going to tell us if it ran... unevenly along the length of it this way, right? So I can do both of those measurements with a micrometer. So when I take my micrometer, what I'm doing is I'm going to put it on a journal and I'm going to get it centered and I'm going to tighten it up. Until it clicks, lock my measurement in place, record that measurement, and you'll notice how on the first measurement I went this way. For the second measurement I want to rotate it a little bit this way, and then for the third measurement I'll rotate it and do it maybe at this angle right here. So now I've got three measurements at three different angles all the way around this thing and if I wrote down each one of those to find out out of round I would just simply take my highest number minus my lowest number and the difference between the two is the amount of out of round I have in that journal. I can repeat that same process on the connecting rod journals measure it in three places subtract the highest and the lowest to get my out of round for my connecting rod journal. Then all I have to do is go look in my service manual and say, Hey! This is the spec. This is what I had. It's either good or it's not good, right? So the out of round is really easy. So is taper. Taper, I would just take a measurement on a, like say this main journal right here. I'm up here toward the top of the journal. Take that measurement, write it down and then drop down to the bottom part of the journal. Take the measurement, write it down and then subtract the two to find out how much taper I have. In a perfect world, when you measure out of round and taper, you're going to have zero. But as an engine wears and you get the load force of the power stroke and maybe improper lubrication and all kinds of other issues that might come up. They can wear unevenly, so if it's a used crankshaft, don't be surprised if you have a small amount of out-of-round or even a small amount of taper. The big important number is the specification in the service manual. It'll let you know if that amount is excessive. So what does it mean when you take these measurements and they are excessive, right? So let's take a look at that. All right so earlier in the video I did mention corrosion and you can see where I had kind of had some lubricant on the journals and that did okay but I'm already starting to build up some corrosion on these side thrusts on these throws and stuff and that's because just the humidity in the air that we've had lately but let's talk about out of round now remember that when you're looking at these guys that there is a bearing that's going to be surrounding these so inside of your connecting rod bores and inside of your main bores You're going to have bearings, a bearing half in the cap, bearing half in the block, bearing half in the connecting rod, bearing half in the connecting rod cap. And when those bearings wrap around these guys, the distance between this guy and the bearing is your oil clearance. Now, if you have taper across the face of this, that means there's going to be a change in clearance across the bearing, which means that what you're going to end up having to deal with is a condition that's going to affect your oil flow. As the oil is coming out of here and trying to go in here between the area between the bearing and the journal, then that flow rate and how it moves through there is going to be affected by that taper. And if you have more clearance on one side than the other, that oil is going to follow the path of least resistance. And you might have the side that has the less amount of clearance have a lack of lubrication in oil, which is going to cause bearing failure and even damage to the journals in some cases. Out of round, remember that the bearings like to conform, so what's a critical measurement that we'll do in another video isn't just the out of round of this journal, but the out of round of the bores that go around it. So I would like to, you know, say I got this connecting rod journal right here, I would want to have that connecting rod, put the cap on, torque it down without the bearing in it and measure the out of round for that rod. And then same thing with the mains. Put the main caps on with no crankshaft in and no bearings and measure that bore for out of round. So but either way you got out of round in the bores, out of round in the journals. It's going to have this a lot to do with bearing conformity and it's going to cause again oil flow issues, oil pressure issues, and maybe even damage to the bearing and journals. So that's why we're taking these measurements is to make sure that basically oil flows and oil clearances are good. Now We'll talk about oil clearances in another video, but that's also critical. A lot of your oil pressure in your engine is developed when that oil tries to force its way out of this hole and get between this journal and this bearing, which in some cases may be like 3,000th, 2,000th. So you have a two thousandths of an inch of clearance and you're forcing oil through there that restriction creates oil pressure and if that restriction grows too much you're going to have a drop in oil pressure and it's a really good indicator that when an engine might need to be rebuilt because it's reached a lot of wear in those components. So anyway this is how to measure a crankshaft. I hope you guys enjoyed the video. If you have any questions make sure you ask. All right, so make sure you ask if you have any questions. Put them in the comments. Let me know what you guys want to see in addition to how to measure. I've done camshafts. I've done crankshafts. I'm right in the middle of an alternator rebuild series that I need to pick up on, but please let me know in the comments what you thought of this video. If I need to make more videos like it or you want me to move on to different topics, just put it out there. One thing I will say is that Memberships help me buy stuff like this, help me buy tools, help me buy parts to make these videos, so consider becoming a channel member. It's a huge support to the channel. Also please remember to be kind to one another out there. Thank you for watching. See you again.