177 | Fitting Bearings To Your Engine
When it comes to fitting the bearing shells into your engine block or connecting rods, it seems like a simple and straight forward process, yet there are a few tips and tricks that you can apply in order to ensure the best life from your bearings and ensure engine reliability.
- Hey guys it's Andre from High Performance Academy, welcome along to another one of our engine building webinars. Now today we're going to be looking at the correct techniques for fitting our engine bearings or our bearing shells into our engine block or our connecting rods. And this is a topic that on face value seems pretty straightforward, pretty cut and dry and very very basic. And to a degree that's absolutely correct. However with our engine bearings and our bearing clearances being so critical to the reliable operation of our engine, and those clearances also being incredibly small, it really doesn't take much to get this wrong and end up potentially damaging your engine or at least affecting its long term reliability.
As usual we will be having questions and answers so at the end of the webinar, if there is anything that I talk about today that you'd like me to discuss in more detail or anything generally related to this topic, that pops to mind and you'd like some answers on, please ask those in the questions and the guys will transfer those through to me. Alright so there are a few aspects to this that we're going to cover off. And a lot of it should be pretty common sense but unfortunately common sense sometimes isn't so common so we're gonna go through everything. One of my key aspects when it comes to performance engine building is never make assumptions so we're gonna start here by not making any assumptions about your level of knowledge or understanding when it comes to these aspects. Alright so the first part here is to actually make sure that the bearing shells that we have been supplied are correct for your particular application.
And there's a range of areas where we can end up going wrong here. One of the first ones is clearly just to make sure that we have the shells suitable for our particular engine. But beyond this there are often some subtle differences within a particular model of engine. A good example of this is the Nissan SR20 DET. Very very popular engine in the import market for rebuilding and modifying and a great basis for a performance build.
Now the SR20 DET engine actually comes in two variants and there's some subtle but very important differences between the bearings that go into both. The common garden variety SR20 DET that we're most likely to come across is the S chassis based SR20, so this is the rear wheel drive, turbocharged and naturally aspirated SR20, that we're likely to find something like an S13, S14 or S15. The other much rarer model is the SR20 DET that came out in the N14 GTI-R Pulsar. This was supposedly a higher spec engine and there are some differences in the engine block and to do with this there are some differences with the bearings, in particular, the main bearings have some different oiling holes and the connecting rod bearings are two millimetres wider. The stock SR20 DET is 17 mil wide, the GTI-R bearings are 19 millimetres wide.
Now that's all well and good, if we get the wrong bearings though, if we try and fit the GTI-R bearings into a stock SR20 DET, they're not going to work. The main bearings require some subtle but important modifications to the actual engine block and the big end or connecting rod bearings, if we install those into a stock SR20 DET connecting rod, they will actually go into the rod, but because they are wider and the locating tang that goes into the rod is in the wrong spot, what we find is that the conrod bearing is actually offset in the housing and we'll find that the bearing shell is actually going to interfere with the radius on the crankshaft journal. So these are the sort of subtle things, of course I've used the SR20 DET as an example here, but these sorts of subtle differences exist across quite a wide variety of different engine types. OK so beyond that, beyond the obvious there, making sure that we actually have the right bearings for our engine, the other thing we need to check is to make sure that we have the right size bearing shells. So in the aftermarket we generally have stock bearing sizes, so this will be suited to an engine that is on stock size for all of its components, the bearing journal in the engine block for example as well as the crankshaft journals.
But then we also have undersized bearing shells that are suited to a situation where the crankshaft is maybe showing some distress on the journal surface and the crankshaft needs to be ground undersize. So these will typically be something like a 10 thou undersize bearing shell. So we can't use these with a stock crankshaft. If we do, we're going to actually have an interference between those components. So obviously should show up pretty easily when we're trying to assemble the engine but it's going to save a lot of time and hassle if we pick this up before we get to that point.
Likewise there are also subtle variations in bearing shell design from different manufacturers. So particularly if we're dealing with an engine that is very common for modifications in the aftermarket, we may find that there are bearing shell manufacturers that supply bearing shells with slight variances in the clearance available, perhaps an additional half a thou or one thou of bearing clearance. This allows us to mix and match and find a set of bearing shells that's going to provide the actual clearance we want. Essentially allowing us to do somewhat of a job of blueprinting the engine and getting our clearances where we need them to be. The last aspect we need to deal with here as well is that the bearing shells that go into our engine aren't always the same.
So what I mean here is we may have upper and lower shells. So I've got a couple of shells here that are from King Performance Racing Bearings and these are going into our SR20 DET. So we'll just have a quick look at these under our iPhone camera. Just see if we can get that so it looks a little bit clearer. OK so these shells here, as we can see, or this particular shell we have a pair of oiling holes in the shell.
Now the important point to note here is that this particular shell is different from the other half which we've got here. So we can see that the other half of the shell has none of those oiling holes in it. These are also distinguished by the markings on the shell. We have a shell that's labelled as a lower and we have a shell, I'll just turn it around so we can see, in the part number here, if we can see this, it has, you can't sorry, but you're just gonna have to trust me, it has a U in the part number which stands for upper. Whereas the opposite side of that shell has an L in the part number which stands for obviously, unsurprisingly for lower.
Now again this is one of those areas that I'd like to think everyone can understand and no one's gonna get this wrong, but clearly we need to make sure that these shells are installed into the engine block the correct way around. These upper shells are designed to go into the engine block, and these holes then obviously align with the oil gallery holes to actually provide lubrication through to the bearing. Whereas the lower shells are designed to go into the main bearing caps that bolt up into the engine block. So again, should get that right but, you know, I'm not making any assumptions here, we wanna make sure that we're covering everything and everyone understands what we're looking for. The last aspect here when we're talking about our bearing shells is that we often could be in a situation where we've got different bearing shells for different locations inside the engine.
So our Subaru FA20 which is just out of shot of our overhead camera here, is a classic example. So what I'm going to do is just temporarily move that over so we can see this and we'll just talk about some of the subtle changes here. Actually we'll go this way I think, might be a little bit easier. Alright so what we can see with our FA20 engine block is that our main bearings, the locations in the block are varying thicknesses or widths. And we need to take this into account when we are fitting our bearings.
In particular here at the back of the block, this last main bearing in the engine block is actually designed to take the thrust washers as well. So this is a one piece bearing so it actually incorporates the thrust washers. So we need to understand that and fit the correct bearings into the correct location. Now often this will be foolproof, we simply won't be able to fit the wrong bearing to the wrong location but again we just want to really overlook everything and make sure we understand exactly what we're dealing with and the exact process we're going to go through. So in this case we have the bearing shells here for our FA20.
I'll just move this block back out of our way. And we'll get these back under our overhead shot. And we've got our main bearings here, so these are our bearings that'll go into the normal locations in the block. And we can see that they've got the lubrication holes which will match up with the oil galleries in our block. But then we also have our thrust washers as well, so these remember go in that last location on the FA20 block, and we've got our thrust washer surface there so this is what supports the crankshaft longitudinally in the block.
So this is actually an old used bearing shell but we do have our brand new set of King thrust washers, thrust bearings that will be going into that engine when it is built. So at this point we've sort of should've ticked most of the boxes and we should know that we've got the right bearings for our application and we know what bearing's going to be going where, we know that we've got the bearings that should be giving us the correct bearing clearance. There are a couple of other aspects before we get to the point of actually assembling our engine though. And when we go through the process of assembling the engine, one of the steps we will take is to measure our bearing clearance. So the other thing we do want to check if we have the ability is to make sure that the housing that the bearing shell is going to go into is also within the manufacturer's tolerance.
Now in most instances this isn't something that is going to wear inside our engine. So essentially we shouldn't have too much to worry about here. But again assumption's something we never want to make when we are building a performance engine. So this does require some specialist measuring equipment. In particular, what we're going to need in order to measure the bearing journal is a dial bore gauge, and we're going to match that with a micrometer.
This allows us to make very accurate measurements of our bearing journal. The process here is much like the process of using a dial gauge and a micrometer in order to check the bearing clearance. What we're going to do is adjust our dial bore gauge so that it's zeroed on the tunnel size for our bearing journal, and then we're going to use our dial bore gauge to actually go into that tunnel with everything assembled, torqued down in our engine block, and we're going to make sure that those measurements do match. There's always going to be a tolerance range in the factory workshop manual, so you just want to make sure that you're within the upper and lower limit of those specs. That also brings me to a really good point here.
When we're building any engine, regardless whether it's for a stock road car or we're trying to make five times the factory power, we always want to start by sourcing a copy of the workshop manual. This is important because it's going to have all of the part numbers, all of the specifications for every aspect of that engine within it. It's going to have torque specifications. Even if we are perhaps replacing some of the fasteners, there's still going to be a lot of factory fasteners that we will be reusing, and most importantly there will be some particular procedures or steps related to a certain engine that we need to follow. For example a good one there is when we are fitting timing chains or timing belts, quite often there are specific procedures that are particular to a given engine.
So sourcing a workshop manual's a great place to get all of that information. These days, thanks to the wonders of the internet, generally if we're dealing with a popular engine, we can find one of these manuals relatively easily and free of charge, just with a simple google search. Now when we are measuring those tunnels as well, as I said, we shouldn't expect any wear, we've only got the bearing surface sitting against that tunnel, so there's no actual movement relative, between the bearing shell and the housing that that bearing shell's sitting in. So this is why we don't expect any wear. However one peculiar situation which I will mention, is where we are building an engine with an aluminium block, like our Subaru FA20 we've got over here.
What we can find is that if we are replacing the factory fasteners that hold, in the FA20's case, the two halves of the block together, the case bolts, or in a normal inline engine, the bolts that hold the main bearing caps into the block, if we replace these with the likes of an ARP aftermarket stud kit which is very very common when we're building a performance engine, we can find that the additional clamp provided by the ARP stud kit can actually distort the relatively soft aluminium block. And what this can do is distort our main bearing tunnel so it's no longer going to be on size, it's no longer going to be perfectly round. So if we overlook this, this is going to affect our bearing clearances. We may actually end up assembling the engine and finding out that we can't even turn the crankshaft depending on how bad the distortion is. So this is one aspect that with any alloy engine, when we are fitting aftermarket studs, as a precaution I would have this checked by the engine machinist during the machining process.
Generally if there is any distortion, they're going to need to fix this, it's not something we can do at home, and this would be done with a process called line honing. So that gets everything back to where it should be. This is a process that we've had applied to our Subaru FA20 engine because we are using an ARP main stud kit. Alright so we'll get into the actual process of assembling our components here. And we're going to start by having a look at the main bearings going into our Honda B18C.
So in this case with our B18C, we've got our three centre main bearing caps, are all connected with an aluminium girdle. Doesn't really matter for the purposes of our demonstration, we're just going to go through and have a look at this. And one of the key points with any engine building process is cleanliness is just so critical. Every step of the way we want to make sure that everything we're dealing with is perfectly clean. So this starts with our bearing caps.
Now a good tip here is to use a white or at least a light coloured cloth. Now the reason for this is if we're using a light coloured cloth, it makes it much easier to tell when we've removed all of the dirt or debris because the cloth is going to come away clean. The other thing we're going to be using a lot of with any engine building is a brake clean product. This is a spray on product that dissolves dirt, it dissolves grease and oil, and it doesn't leave any film on the surface. So I use a lot of it, all I'm going to do there is just spray this on my rag and then we're going to clean out the bearing surface, or the surface that the bearing is going to sit on.
And we're looking for basically what's coming off on our rag. So we can see there we've got a little bit of dirt and a little bit of oil. In this case our housing is relatively clean. Now that's OK, we're dealing here with relatively clean parts to start with. That's not always going to be the case so I just want to bring out a bearing cap that's off our LS1 project that we're dealing with.
So we started here with an LS1 that was a bit of an unknown origin engine. It was sourced from a wrecker, it was incredibly cheap, it was probably barely worth what we paid for it. It looked like it hadn't been serviced in about 350000 miles and it was filthy inside. That's not gonna be uncommon when you're dealing with unknown origin engines though, not everyone looks after their engines as well as they should. So if we can go to our overhead camera, this is what the housing looks like after a relatively quick clean.
And in fact what I'll do is I'll just set up our iPhone camera here. And we'll just switch across to that and get a better look at that. Just get a little bit tighter in. OK so the problem with this is that our housing is still filthy. And in particular what we're got is a lot of gum built up around the outside of this housing where the old shell was sitting.
And that is not gonna come off with brake clean on its own. Likewise we've got a lot of gum or varnish residue sitting in the locating cut out, where the locating tang on our bearing sits. And that's also going to be a problem for us. So if we simply clean this cap down with brake clean and fit a bearing shell, particularly if the bearing shell we're fitting is marginally wider than the one that came out of there, it's gonna be sitting on that layer of built up varnish and crud and that's going to potentially affect our bearing clearance. So when we've got a situation like this we need a slightly more aggressive way of cleaning the bearing shell, the cap down.
So that's where I use green scotch brite. So this is great for cleaning away that sort of crud. And I'm going to just give this a bit of a spray down and I'm also going to apply a little bit of brake clean to our scotch brite, just helps the process. Let's have a look at this under our overhead camera. So all I'm going to do is just go backwards and forwards in our housing here and obviously this can take a little bit of time depending on exactly how filthy the cap is.
But hopefully we'll quickly see sort of a clean patch emerging where I have spent some time there. Alright so once we've gone through and given that a bit of a clean down with our scotch brite, we can then go through with our brake clean and a clean rag and let's just go back under our iPhone camera. So again we can just see the difference there, where I have been cleaning that with our scotch brite is is nice and shiny now, nice and bright, there is none of that residue there. Likewise we also need to clean out that little locating tang. And there's a variety of tools we can use for this.
I've just got a small wire brush. It's quite a soft bristled wire brush, it's not actually gonna scratch or damage the surface of that cap. But it's great for getting into tight little spots and removing all of that crud out of that locating tang. So we really wanna make sure that everything is essentially sparkling clean before we ever consider fitting our bearing shells into the cap. Alright so we'll bring our Honda B18C caps back in here, back under our overhead.
And the next aspect we need to consider here is the parting line where these caps locate against the block. And I'm just gonna point this out here on our iPhone camera. So what we've got here is this parting line here which is where we're going to be locating our bearing shell into. On the opposite side we've got the little locating cutout in the cap, which the tang on the bearing shell's going to go into. And we want to be very careful because this is quite sharp here, this surface.
And if we aren't careful when we're inserting our bearing shells, what we're going to end up doing is scraping material off the back of the shell. So that's something we need to be really careful of when we are inserting the shell. So we're going to go through a step by step process and see how simple it is to do that right and make sure that we don't end up scraping material off the shell. Before I do that though, I will just go through the process of cleaning down the shells. And obviously that's pretty straightforward.
We've got a set of ACL bearings here that are going into this B18C. And again the process is simply to use brake clean and our rag, and we wanna make sure that if these have just come straight our of the pack, they're going to have a protective layer of lubricant or oil, preservative on them. We want to make sure that that's all removed and we also want to make sure there's no dirt or debris on them. It's a good idea also with our bearing shells to carefully inspect the shells and make sure that there are no nicks or marks, no obvious sign that the shells have been damaged in transport when you do go and open them. If they have, you want to obviously take those and get rid of them and start again with another set of bearings that are showing no signs of damage.
Before we go and insert that bearing shell though, there is one more aspect that we may want to consider. So if we are using a bore gauge to check our bearing clearances, which would be the approved way or the ideal way of checking and confirming our bearing clearances, then we can be in a situation where the bearing shell is going to show a little bit of distress on the surface. So what we've got, I'll just grab our bore gauge again. And essentially when we're using the dial bore gauge, it's going to be inserted into the housing and we end up with the little wheels as well as the little plunger on the dial bore gauge, will be rubbing against that bearing shell. And the surface of the bearing shell is reasonable hard but we can still end up with that leaving a mark.
Now a point there, this particular bore gauge does use little teflon buttons on both the plunger as well as the extension. So this does help reduce the marking from the dial bore gauge, but it's still a situation we will end up dealing with. We're going to have some marking, so hopefully we will be able to show you this on our iPhone camera. Yeah that's sort of coming out, we can see that there are some little scrape marks on our bearing shell, we can see those there, we can see some matching ones on the other side of that shell, and then we've got one from the plunger down through the centre of the shell. Now this is a common question I get asked, is what do we do about these? While they do look a little bit ugly, they're actually not as concerning as you may think.
And particularly if you actually run your finger across those, you're not actually going to be able to feel them. That being said, we can remove those marks quite easily. And what we're going to do here, this sounds a little bit scary, but bear with me, you'll see how easy it is. What we wanna do is grab some fine emory paper. Now don't get scared, I'm not actually going to be using the abrasive side of this emory paper on our bearing surface, this is the important aspect of it.
What we're going to be doing is using the relatively smooth backing from our emory paper. So what we want to do is just rip off a small section of that emory paper. And we want to give that a light spray with a lubricant. So here I'm just using CRC but basically any lubricating oil will be suitable. And then we want to take our emory paper, remembering again we are not using the abrasive side of this paper, that's absolutely critical to understand.
Gonna turn that over and going in the same direction as the crankshaft is going to rotate we're just going to gently rub that backwards and forwards in the bearing shell and what we'll find is that that's going to polish out those marks. So it's really easy to do, we don't need to apply much pressure at all. And all we're doing is using the very very light abrasive nature of the paper on the backing of our emory paper in order to just remove those marks. So I'll just clean that down, obviously once we've done that we also want to make sure that we thoroughly clean it again using our rag and brake clean. And I'll see if we can then show you that again under our iPhone camera, so let's head across to that.
So we can see there, those marks are all but gone. I mean that was just a light rub with that paper. If you've got some marks that are a little bit more stubborn, you can spend a little bit more time with it. Obviously we don't want to end up removing any material from our bearing shells that could end up affecting our clearances, but all we're doing there is basically polishing that surface of the bearing shell and removing those marks. Alright let's move onto the last part of our demonstration here, so we are gonna be moving into some questions and answers really shortly so if you do have anything that you'd like me to discuss further, now is the ideal time to ask those.
So what I'm gonna do is go through two demonstrations here. We're going to show you the wrong way of installing these bearing shells and then we're going to show you a simple technique that's gonna make sure you're not gonna do any damage. So again I'll just try and set this iPhone camera up so we can see what's going on here. I think that'll work quite well. So what we're looking at here is that sharp edge.
So what we want to do is take our bearing shell, obviously we've already cleaned that down. We've got our locating tang, we know that we've got the correct bearing shell for this location. And what we're going to do is start by inserting the locating tang into the matching part of the housing, I'll just get that installed there. So this is the way a lot of novice engine builders will go about it. They've got the bearing shell sitting there loosely, and then all they're going to do is apply pressure directly down with their thumbs.
And what we find when we do this, is often that's going to result in material being scraped off the back of the bearing shell, and that material, in this case it actually hasn't done much, so that's not a great help to my demonstration, but what we end up with is these little scrapings end up sitting here along the parting edge of our main bearing cap and sitting on our bearing shell. Now the problem with this is that obviously first of all, we're removing material from the bearing shell, that's not particularly important along the parting line. There is some eccentricity built into our bearing shell and really the main load bearing from our bearing shell, is vertically up and down so perpendicular to the parting face. So that aspect isn't too critical but of course what we've now done is introduce some fine debris, little scrapings there that can end up passing through our lubrication system and causing premature wear. So that's really our biggest concern there.
So what I'm going to do is we'll just push that bearing shell back out. If we look at our bearing shell actually under our iPhone camera, I'll just get this out of the way and have a quick look. We can actually see some signs of that scraping right on the edge of that particular shell. So it is actually showing what I'm trying to discuss here, trying to explain. We'll bring our bearing caps back in and we're going to go through that demonstration one more time.
And what we're going to do here is again locate that tang into the matching part of our housing. Once we've got that located, this time what I'm going to do is I'm going to apply pressure forwards with my two thumbs. So what I'm trying to do is actually push the bearing shell forwards towards the other side of the housing, and what this is going to do is have the affect of slightly compressing the bearing shell, making it slightly narrower, and that'll allow me to then drop it into the housing without scraping the back of the shell. So we'll just go through that process now. And it is actually really easy to do, we don't need to apply much force to that bearing in order to just compress it slightly.
Our bearing shell's now in the housing and there's no chance of any of that material being removed from the back of the bearing, we're comfortable that everything is exactly how it should be. And we'll be able to move on with our engine building process. Now before we jump into our questions and answers, I just wanna talk also about the next step of that process, once we've got our bearing shells installed, which will be applying some lubricant to the shells. Now there are a couple of schools of thought here and I've actually changed the product that I use over the years I've been building engines. What we find is that there are some specific engine assembly lubricants out there on the market from a variety of different manufacturers.
And these are designed to provide additional protection to our engine components during initial startup. During our initial startup, it can take quite a long time for us to gain oil pressure so we want some protection from our bearing shells and our crankshaft journals while we're going through that process. So these lubricants, we can use them, but the problem that I've found with them is that they tend to be quite viscous, quite thick compared to normal engine oil. Now that's not necessarily a bad thing, it's certainly not going to be a negative to our engine performance. Obviously that all just washes out and we end up getting rid of it when we do an oil change.
But from and engine builder's perspective, a lot of what we do relies on the database that we build up in our own minds of experience of how an engine should feel when it's assembled. Obviously you're not gonna have this when you first start building your very first engine, but you do build it up as you build more and more engines, and you tend to work out what feels normal and what doesn't. So one of the first things any engine builder is going to do once they've assembled the crankshaft into the engine block, is they're going to grab that crankshaft and give it a spin. Now that's sort of one of those checks we do just to make sure that everything spins and turns freely, there's not tight spots, and we can rotate that crankshaft easily by hand. Now if we're using an engine assembly lubricant because it is more viscous, and this tends to get worse if we live in a part of the world where our ambient temperatures are very low, like they are here in Queenstown right now in the winter, what we find is that this makes the viscosity, the thickness of the assembly lubricant even worse.
So it can actually be quite hard to turn that crankshaft and this can be a little bit concerning. It may not actually indicate there's any problem as all, it's just a case of that heavy thick oil coupled with the fact that it is cold, makes it just a little bit harder for us to turn the crankshaft. So what I actually use for lubricating my bearings prior to assembly, is just a clean, mineral based oil. And I've basically been using that for about the last 10 years and I've never had any problems with that. Now don't get me wrong, there are still areas where I prefer, to use a assembly lubricant.
Some of the areas which are a little bit more heavily loaded, some of the valve train components for example, the wrist pin in the connecting rod and the piston. Areas which will take a little bit longer to get proper supply of oil inside the engine. But as far as the bearings go, I actually assemble these just using clean fresh motor oil. Alright we'll have a quick look at the questions we've got here. Our first question comes from Geoffrey who's asked, how do the amino acids in skin oil affect the bearings? That's actually a great question Geoffrey, it's not something I've ever taken too much consideration of.
So when I'm assembling an engine, I'm going to be assembling those components basically as soon as they've been cleaned. So generally with a bearing shell, while I am touching it now, I'm gonna be using the brake clean product to clean both the backing and the surface of the bearing shell. After that there's no real need to touch the backing of the bearing shell, it's going to be assembled into the housing and then straight away we're going to be giving the bearing shell another quick wipe with a clean rag and brake clean and generally then we're going to be applying a assembly lubricant or our engine oil to the bearing shell. So I'm not sure of long term effects of that but I've certainly had bearing shells sitting around the workshop for extended periods of time which I will have touched with my bare hands and I've never seen any negative effects of that. If you are worried about this, of course there are gloves that you can use for your engine building.
John has asked, for the B18 crank bearings are ARP studs OK to use for the crank caps and girdle or would OEM studs be OK to use for a 500 horsepower goal? Look for 500 horsepower I would probably be recommending that you swap to an ARP stud kit. As I mentioned in the body of the webinar, particularly with the B18C, you will see some distortion of that main bearing journal when you use an ARP stud kit due to the additional clamping force. So line honing during the machining process is an essential in my opinion on the B18C. But generally for just about any engine project I'm involved with where we are aiming for a significant step up from the factory power output, a stud kit through the main bearings and also a head stud kit will just be sort of normal best practice really. The Drift Ninja has asked, I recently purchased ACL race bearings for a fairly low kilometre Nissan CA18 DET engine rebuild.
They are one thou undersize, the crankshaft journals are really good condition and I'm hoping the machinist can target equal clearances when polished in the crankshaft. I want to target two thou clearance on the rods and mains for street and occasional track day, does that all sound realistic? Yeah OK so probably if your crankshaft is in good condition and doesn't need grinding, and it measures up on size, you're probably going to find that there's no need to go to an undersize bearing set. When you're going to an undersize bearing shell, generally this will be so that you can grind the crankshaft, and I'm thinking there whether you've actually got a one thou or a 10 thou, there's two different sort of areas that we deal with here. So I generally, when we're going with an undersized bearing shell to allow the crank to be ground to recover it from damage to the journal, we'll be going to a 10 thou undersize shell and this allows a reasonably significant amount of material to be removed from that journal to get it back to a good surface finish. Then there are some performance bearing shells which generally when we're building a performance engine and we're extending the power well beyond factory and potentially the rev limit as well, what we will typically do is build an engine specifically and purposefully with slightly looser clearances in the oil department than the factory specification.
So we do find some shells, some bearing manufacturer's offer shells that offer additional clearance and that would be in the order of one thou. Now all of this being said, if you are grinding the crankshaft, and unless it was necessary, I definitely wouldn't recommend it, one of the problems we see is that factory crankshafts are induction hardened so the surface finish of the crankshaft and those journals is actually hardened. But that surface, that hard surface is very thin so when we grind the crankshaft undersize, we're going to end up grinding through that hardened surface. So this affects the long term durability of the crankshaft. It doesn't really affect the strength per se.
What it does affect is the ability of the crankshaft journal to not be scored or marked by the inevitable debris that we're going to have going though our oiling system. Really long answer to your question there, two parts I will reiterate there, your targets on clearance probably sound reasonably realistic, it's been a long time since I have built a C18 DET. Good rule of thumb is we allow around about one thou per inch of crankshaft journal diameter. I always base this of course though on the factory specifications. And if I'm building a high performance engine I'll typically go slightly looser on the loose side of those tolerances, two thou sounds like it would probably be about right given my knowledge of that engine.
And again if that crankshaft doesn't need to be ground, I'd probably be sourcing a stock size bearing shell from ACL. James has asked, is there a product that you've used successfully while the engine is assembled in the car to clean the journal, oil journals, passages between oil changes? No I think, I get what you're talking about here James. It can be a little bit depressing when you're doing an oil change on your car and you go and drain all of the oil out, do as good a job as you can, and then you go and tip some brand new oil in, often quite and expensive oil and you find out within sort of the first few hundred kilometres of driving that it's really discoloured quite quickly and a lot of this obviously can be to do with the oil that we can't drain out of the engine. I've never really come up with a technique of doing a better job of that and the only real way to do it probably would be to disassemble the engine, not very practical every 10000 miles of use. Barry's asked, how would that paper technique affect a bearing like King bearings that carry the pMAX coating? That's a really good question Barry 'cause we do have some King bearings here with the pMAX coating.
If you have got a coated bearing then yeah that's not something I would recommend, it is going to affect that pMAX coating. What I have found actually with the King pMAX coated bearings though is that the surface of the bearing is actually incredibly hard and that's one of the aspects that the pMAX coating is designed for. With the FA20 engine running those King bearings with the pMAX coating, we've actually found that the bearings didn't even mark up with our bore gauge so potentially a moot point. Obviously the more expensive option is if you have marked those bearing shells, then you buy one set for your dummy assembly and your measurements and another set that will actually go in for the final assembly. Obviously adds to the costs but that is one way to ensure that the surface finish of the bearings is unaffected.
Adam has asked, could all of this also apply to cast iron engine blocks that are used in Falcons? I'm not sure what aspect you're talking about there, whether that was to do with the ARP main studs. Not an engine that I've personally had anything to do with, but it is definitely possible if that was what you were talking about there, the distortion aspect. So again if there's any doubt at all, it's one of those things that we can easily have the machinist measure. It's one of those things that is easiest to have the machinist measure. It's not gonna really add a lot to your machining costs.
But the reason we wanna do this is because if there is a distortion there then we're going to have to get the engine block back to the machine shop for line honing anyway. We can't fix this in our home workshop, so you may as well find out that problem there and then and deal with it if it is an issue. Barry's asked, if you're mixing bearing shells with different sizes, which bearing would you put in the crank cradle and thicker bearing shell or the thinner bearing shell? This is gonna really come down to what sort of bearing shells you're dealing with. So there's two aspects here. If you are dealing with a factory engine that uses graded bearings, this is quite common in a lot of performance engines now, probably most performance engines run this way.
So what we have there is a grid basically in the workshop manual where you'll have numbers or crankshaft journal sizes versus the journal sizes or numbers on the engine block, and you're going to match those and it'll give you a colour code or grade for the bearing shells that you're going to order for that particular journal. In that case, with a factory engine, you're going to be using the same bearing shells for the upper and lower locations. If you're dealing with aftermarket bearing shells though, it's gonna depend on what availability you've got there. And in this instance I don't really know if it's going to make a huge amount of difference there whether you're using the thicker shell on the upper or the lower location. Julio has asked, what would you recommend as a good internal setup for a B20B? Probably a little bit beyond the scope of this particular webinar, and pretty difficult for me to answer on the basis of the amount of information you've given there.
Is it naturally aspirated, is it turbocharged, is it supercharged, are you planning to use nitrous? So I think we'll pass on that one there, just really off the topic of bearings alone. Geoffrey has asked, when installing studs, should they be run all the way down or run down and backed off a turn and marked so any rotation during assembly can be monitored. OK so when you are fitting studs, you do actually want to bottom these in the block and you also want to start by making sure that the threads in the block have been cleaned out. So it's always a good process, I go through this during the block preparation step. I'll actually just run a bottoming tap through all of the bolt holes in the block and make sure that they're all clean of debris and then yeah we want to install those studs all the way to the bottom.
Now they don't need to actually be torqued down, they also don't need any Loctite product, any product to actually stop them moving. What we need to do is just tighten them down finger tight and then just give them a slight nip up, often the aftermarket stud kits that we will be dealing will have an internal hex on the end of them so this makes it really easy to do up. We also will find that there are some stud kits available that have an extension on the end of the stud and this is designed to bottom in the stud hole and this just ensures that there isn't any undue stress placed on any of the threads on the stud itself. I've got one more question here. Marcus has asked, what's your thoughts on WPC treatment on bearings? It's a great question Marcus, it's not a process that we have easy availability to here in New Zealand.
And I have followed Moto IQ actually really big proponents of WPC treating, so if any of you have read any of the Moto IQ blogs or engine build blogs you will have almost inevitably seen them referring to WPC treatment. It does make a lot of sense. I'm not 100% convinced how much use it would be on a bearing shell. So the WPC treatment as I at least understand it is going to be a really good treatment to apply to any products or any parts of the engine that are going to be contacting one another. This reduces friction massively and the other part of the process is that it reduces wear on those components.
With the bearing shells, and this is something that a lot of people don't sort of take into account and overlook, is that we should be seeing no metal to metal contact between the crankshaft journal and the bearing shell. If that actually happens, basically no surface treatment in the world is going to save you, you're going to end up damaging both the crankshaft journal and also the bearing shell. So we need to be really really careful about that. We always rely on that protective layer of oil between the bearing shell and the crankshaft journal. So because we don't have the metal to metal contact there, this is what makes me just wonder a little bit about the WPC treatment on the bearing shells.
Of course there is the aspect where it could reduce the friction between the oil film and the bearing shell, beyond that, I haven't tested it, I can't unfortunately say too much more about it. Probably I will leave that with, there's unlikely to be downsides as far as I can see from that WPC treatment though. Right I've got one last question here from Geoffrey who's asked, can an abraded coating be used on engine bearings? Not 100% sure what you're actually referring to there Geoffrey. Just really sort of reiterating from Marcus' question there with the WPC treatment, I haven't personally been involved with applying any coatings or treatments to bearings. I am relying on bearings as supplied from the manufacturer.
We had a question there a little bit earlier from Barry about the pMAX coating on the King Performance Racing bearings. So this is the sort of manufacturer coating that I would be using in our performance engines but aftermarket coatings on the bearings are not something that I've personally used. Alright guys we will leave it there. Thanks for all of those questions, some great ones in there. As usual for our members, if you do have any further questions that crop up after this webinar has aired, please ask those in the forum and I'll be happy to answer them there.
Thanks to everyone who has joined us and I look forward to seeing you all next week, thanks guys.