Practical Engine Building: Step 5: Balancing Parts
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Step 5: Balancing Parts
23.42
| 00:00 | In the next step of our process we're going to look at balancing some of our engine components. |
| 00:04 | This is namely going to be of course the pistons and the connecting rods. |
| 00:06 | We don't have the ability to balance the rotating assembly of the crankshaft, the flywheel and the clutch pressure plate ourselves and we've left that up to our engine machinist. |
| 00:17 | However, these components, while you can have your machinist balance these as well, in our case we're going to do these here and now and this is absolutely within the capability of any home enthusiast and doesn't require a huge amount of equipment. |
| 00:30 | We will need a set of scales that are able to measure down to a tenth of a gram and the repeatability of the scales is also really important for this balancing process. |
| 00:39 | We've got all of our components laid out here, we'll start with our pistons because these are a little bit simpler to balance and we're not just considering the weight of the pistons themselves, I like to consider the weight of the entire assembly, the wrist pin, the wrist pin locks as well as our ring set. |
| 00:58 | Although, admittedly, typically we don't see a big variation in mass across those particular components. |
| 01:04 | So, let's just compare a couple of these and see if they are measuring up the same. |
| 01:08 | Let's start by checking out the weight of our wrist pins, we'll start with our number four wrist pin, get onto our scales and we can see 73.2 grams there. |
| 01:17 | We'll try number three wrist pin and we've got 73.2 grams there. |
| 01:23 | So, basically all of our wrist pins work out to be the same mass. |
| 01:28 | Let's now move on and check out our ring set along with our wrist pin lock. |
| 01:33 | So, again we'll take the set from number four piston here and we'll get that all onto our scales together. |
| 01:42 | And we've got 23.4 grams there. |
| 01:46 | We'll try again for number three. |
| 01:51 | And we've got 23.4 grams there. |
| 01:53 | So, as we'd normally find, our wrist pins as well as our wrist pin locks and our ring sets are essentially identical across our four sets of pistons. |
| 02:02 | The good news for us there is that means we can disregard those weights and we're going to concentrate solely on the weight of the piston themselves. |
| 02:10 | So, let's just take a measurement across our four pistons here, we'll start with number one, get that nice and central on our scales. |
| 02:18 | And we've got 334.8 grams so we'll write that down. |
| 02:22 | We'll go through the remaining pistons here and get all of their base weights measured. |
| 02:29 | Alright, so looking at our piston weights here, we can see that three of them are actually really really close to each other. |
| 02:35 | We've got number one, number three and number four all within 2.2 grams. |
| 02:41 | And that's pretty good coming straight out of the box. |
| 02:44 | Unfortunately, we've got this one outlier here, number two piston , which is 333.6 grams. |
| 02:51 | So, basically one gram lighter than three and four, 1.2 grams lighter than number one. |
| 02:58 | So, we've got a little bit of work to do here. |
| 03:00 | Unfortunately, this means that we've got three pistons that we're going to have to remove some material from in order to match the weight with our lightest piston, number two. |
| 03:10 | So, what are we aiming for here? Well, that really does come down to personal preference and a lot of aftermarket piston manufacturers will balance to within a gram, which essentially we're pretty well there as it is. |
| 03:24 | I like to try and be a little bit tighter with my tolerances than that and realistically when it comes to balancing the piston, it's not that much more effort to balance within half a gram as it is to balance within maybe plus or minus 0.1. |
| 03:37 | So, I'm generally going to be aiming for that plus or minus 0.1 although I will freely admit that that is probably being a little bit excessive, but again doesn't take a lot more work to do. |
| 03:49 | So, we also need to understand where we can safely remove material from these pistons and these are quite a lightweight piston being that they are designed for a high RPM naturally aspirated engine. |
| 04:00 | Obviously, any time we're removing mass from the piston we want to do it in a way that we're not going to be compromising the strength of the piston. |
| 04:07 | Again we can see we've got this strutted design on the underside of the piston here. |
| 04:12 | Not a lot of excess material in the pin bosses and what I would be looking to do is remove some material from these four corners here as well as potentially the external corners here. |
| 04:25 | We can also shave a little bit of material from these struts. |
| 04:28 | So, it's a case of removing material evenly and we want to remove as little material as we can get away with while achieving our aims of obviously balancing our pistons. |
| 04:38 | Also when we are doing this, it's always a good idea to essentially measure twice, cut once and what I mean by this is track your progress by taking measurements on the scales frequently and this is going to help prevent you overshooting and taking away more material than you actually need to. |
| 04:55 | Obviously, this is going to waste time and then you end up in a bit of an iterative cycle of now going back to what was your lightest piston and having to remove material from there as well. |
| 05:06 | Now, how am I going to be removing this material? Well we're going to be using the same battery powered die grinder that you saw me use during the block preparation step that we've just completed. |
| 05:16 | Air powered die grinder would also be absolutely fine as well as a Dremel, this is another option. |
| 05:23 | And in fact I will be using a Dremel with a sanding roll on it, we'll get this under the overhead camera here. |
| 05:31 | And this sanding roll is going to be used once we've got the weight down to essentially where it needs to be. |
| 05:37 | And the reason I'm doing that is that when we use the die grinder, this tends to end up with a relatively coarse finish to the underside of the piston where we've removed that material. |
| 05:48 | This can be a source of stress raisers, so I just like to smooth that out with a sanding roll. |
| 05:52 | Alright, so we've got our first piston here, number four, and we know that we essentially need to remove one gram of material from that piston to get it right onto the same weight as number two, so let's go ahead and do that now. |
| 06:16 | Alright, so we've gone through and removed some weight from number four piston. |
| 06:20 | However, I've got this down to now 334.0 grams so we've taken 0.6 off that piston but we're still 0.4 heavier than our number two piston and of course if we're looking at a plus or minus 0.1 tolerance, that would allow us to be as heavy as 333.7 so we're 0.3 off that. |
| 06:44 | However, I'm making a judgement call here that I'm going to put up with that slight imbalance there that's outside of what I was aiming for, because if we have a better look at the underside of the piston, and again this really just comes down to the design of the piston, I'm conscious now of how little material I actually have available to remove and we will get ourselves into this situation from time to time. |
| 07:09 | And essentially I'm a little bit cautious now that if I start removing more material from this piston, I risk actually weakening it and to me that makes no sense, it doesn't matter how well balanced the piston is if it's going to fail quite shortly after it's put into service. |
| 07:25 | So, at this stage we're now within plus or minus 0.4, well we're 0.4 heavier , which is still much better than the tolerance that Wiseco supplied these pistons to and certainly within the realms of what most engine builders will consider to be a fairly tight tolerance anyway and this is really again just a judgement call, but as soon as we get to a situation where we're starting to reduce the mass of the piston by taking material away that's adding strength, that's obviously the last thing we want to do. |
| 07:58 | So, in this situation I'm going to stop at this point and we'll see how we can get on with the remaining pistons and how close we can get them. |
| 08:07 | Chances are that our number one piston, given that it's 334.8, we're probably not going to be able to get that down to that 334.0 that we've just done. |
| 08:19 | So, again it's just a compromise that we're going to have to make in this particular instance given the design of these pistons. |
| 08:26 | Now, another thing I just wanted to mention here as well, we'll bring my die grinder back into shot here and what I've actually done is swapped to a coarser carbide cutter, tungsten carbide cutter and we will find when we are dealing with aluminium that the finer tungsten carbide cutters that we'll normally find with this style of die grinder, they will actually clog with aluminium material quite quickly and that will basically make them ineffective for cutting. |
| 08:55 | So, this coarser style is designed for aluminium and it remains clean so you're not going to have a problem with clogging, so that's just something to consider if you are purchasing a die grinder and you are having problems with the tungsten carbide cutter clogging up. |
| 09:08 | From here let's go ahead and we will try our best to match the weights of the remaining two pistons. |
| 09:15 | Alright, so at this stage we've gone through with our first round of changes and I've actually managed to get number one and number three down to 333.8 grams. |
| 09:27 | So, that's actually pretty close to our mark, plus or minus .2 now. |
| 09:32 | I'm going to just try and get a little bit more material out of that number four piston, that was the first one that we looked at and as you sort of go through these, you start to get a bit of a feel for where the material can come out. |
| 09:45 | I've obviously managed to get a little bit more weight out of number one given that it started as the heaviest, I've managed to get a full gram out of that. |
| 09:52 | So, we're just going to have another look at number four piston and see if I can get that a little bit closer to the mark without risking any damage to it. |
| 10:00 | Alright, so ultimately we did get our number four piston down to 333.8 grams. |
| 10:06 | So, another 2.2 of a gram out of that piston. |
| 10:08 | So, we've got now three pistons sitting at 333.8 grams and now number two, our lightest piston, 333.6 grams. |
| 10:16 | And again not quite the plus or minus .1 that I was aiming for, we're 2.2 of a gram spread between heaviest and lightest, but again that's actually pretty tight and definitely significantly better than what Wiseco delivered. |
| 10:29 | So, I'm happy with that, does leave the remaining task though of going through and just using our sanding roll to clean up any roughness left with our grinder. |
| 10:41 | This typically is going to not affect the weight significantly, not enough to affect what we're actually measuring here with our scales, but of course once we've completed this, it's always worthwhile just checking to see if we have affected the balance. |
| 10:55 | So, let's go ahead and do this to one of these pistons now and we'll have a look at the results, we'll start with our number four piston. |
| 11:01 | And what we can see if we look carefully is we do have a slightly rough surface finish here , which is completely understandable given the coarseness of the carbide cutter that I was using. |
| 11:16 | So, what we're going to do now is use our sanding roll on our die grinder and we're just going to run that across and smooth out that finish and we'll have a look again at the finish once we've done that. |
| 11:39 | Alright, we've completed that process on our first piston and straight away we can just see how much nicer that surface finish is, we've got rid of those sharp edges that we unavoidably end up with when we're using a tungsten carbide cutter. |
| 11:53 | And again just getting rid of those sharp marks should help make our piston a little bit more reliable, less chance of any cracking beginning as a result of some of those sharp edges. |
| 12:04 | For the sake of completeness, let's just see how that has affected the mass of our piston. |
| 12:10 | And we can see we've actually ended up going down another tenth of a gram. |
| 12:13 | As I mentioned, usually we're not removing enough material with the sanding roll to actually affect the weight of the piston, but we always want to check that. |
| 12:22 | So, this brings us down to a tenth of a gram from our lightest piston number two. |
| 12:28 | But when I was talking about our tolerance before of plus or minus .1 that I'm actually aiming for, we actually were already there. |
| 12:35 | Maybe my thinking was just a little bit slow before when I was talking about it , but of course if we're looking at a tolerance of plus or minus .1 it is exactly that and if we take our centre point at 333.7 of a gram, minus .1 obviously takes us to our lightest piston and plus .1 would take us to 333.8, which was what we ended up with the rest of the pistons. |
| 12:57 | However now we've tightened that tolerance up a little bit for our number four piston, I'm just going to go ahead now and repeat this process with our remaining two pistons that we have modified. |
| 13:06 | Of course, understandably we haven't done any grinding work on number two pistons so we don't have to touch that. |
| 13:12 | So, let's get our other two pistons dealt with now. |
| 13:15 | Alright, we've gone ahead at this stage and repeated that process on the remaining two pistons so we'll go through and get our final weights. |
| 13:22 | So, as we can see there, we've actually ended up, despite my initial concerns, getting our pistons all within 1 1⁄10 of a gram, which again as I mentioned at the start, very tight tolerance and not necessary that you do work to that tolerance, but again when you're doing this work, it's not a lot more work to shoot for plus or minus half a gram than it is to shoot for plus or minus 1 1⁄10 of a gram, so I don't mind putting in a little bit of extra effort , but as we've seen in this situation, we do have to assess the piston that we're dealing with and sometimes we might need to compromise our tolerance in order to maintain a safe, reliable piston that's not going to be weakened by our lightening process and this all really comes down to just understanding the design of the piston and seeing where there is a little bit of excess mass in that piston that can safely be removed without compromising the strength. |
| 14:14 | So, once we've finished with our pistons, we'll get those off the workbench and we'll start addressing our connecting rods. |
| 14:19 | At this point we've got our conrod weighing fixture set up with our scales, we've got our connecting rods laid out and we're ready to start taking some measurements. |
| 14:27 | The process of this follows what we've looked at in the body of the course, we're going to begin by weighing the big ends of each of the connecting rods, remembering that we have to separate the rotating and reciprocating masses with the connecting rod, it's not just a case of balancing the overall weight of each of the rods. |
| 14:44 | The conrod weighing fixture is a little bit fussy in order to get good repeatability. |
| 14:50 | So, as per the body of the course, what we're going to do here is go through, we'll take five measurements of each big end, what we're going to do then is reject the highest and lowest and average the other three. |
| 15:02 | So, this can be a fussy, fiddly and time consuming process, but let's get our scales turned on, we'll let those zero and we'll begin with our number one connecting rod. |
| 15:12 | In order to get good repeatability or the best repeatability we can, what I do like to do is make sure that I'm always locating the connecting rod in essentially the same place on our scales. |
| 15:24 | So, our first measurement there for number one connecting rod, 380.0, so we'll write that down. |
| 15:31 | Alright, we'll go ahead now and take another four measurements. |
| 15:43 | Ok, our first conrod, our big end weighed five times and we can see that we've actually got reasonable consistency , which is always refreshing. |
| 15:50 | Our lowest value there, 379.5 grams so we're going to reject that value. |
| 15:55 | Our highest, 380.3 and now we can go ahead and average the remaining weights. |
| 16:03 | In order to average the three, we'll just simply use our calculator. |
| 16:06 | So, we can enter 380 plus 379.8 plus 379.7 and we'll divide that by three and we can see we've got 379.8, rounding that to one decimal place. |
| 16:22 | So, let's write that down. |
| 16:25 | We're now just going to go ahead and repeat this process for our remaining four connecting rods. |
| 16:31 | Alright, that's our initial measurements made of the big ends of the connecting rods and straight away we can see that we've got a lightest at 379.2 and our heaviest at 381.6 so almost 1.5 grams difference just on the big end of that particular connecting rod which is certainly a little bit outside the scope of where I'd like to see the weight. |
| 16:52 | So, we're going to now attempt to remove some weight from the heavier rods and try and match these to the lightest of course, our 379.2. |
| 17:01 | And here I'd like to be within half a gram or better of our lightest connecting rods. |
| 17:07 | So, we also need to understand where abouts we can remove material safely so we'll start with our number one rod , which we know is a little bit heavy, we're going to need to remove a little bit of weight from there. |
| 17:17 | Now, we get this under our overhead here. |
| 17:19 | So, what we're looking for is areas where we can safely remove material without risking damaging the rod. |
| 17:25 | And it is always very tempting to remove material from these ridges on the big end cap. |
| 17:30 | However, these are actually there for a purpose and these strengthen the cap and make it more rigid, less likely to flex so we actually want to leave that material intact. |
| 17:40 | So, what we want to do is remove material down the edges here of the area of the rod where the bolt goes through. |
| 17:50 | So, we can actually remove a little bit of material here without risking damaging the rod or adversely weakening it. |
| 17:56 | While we're looking at this as well, when we do get to the point of removing material from the pin end or small end of the rod, what we're going to do is use our linisher and linish evenly around the outside diameter of that small end of the rod. |
| 18:09 | Looking at the thickness of the material there, what we want to do is remove that material as evenly as we can so that we don't end up with one spot that's a little bit thinner than the rest. |
| 18:21 | So, it's a case of very smoothly and evenly removing that material using our linisher. |
| 18:26 | So, now that we understand what we're going to be doing, let's head across to our linisher and we'll start removing some material there. |
| 18:32 | Just as we did with the pistons, it's always best to remove that material slowly and check your work frequently rather than finding you've removed too much material and you've overshot. |
| 18:43 | Just like with the pistons, depending on our level of imbalance and the amount of material we can safely remove, sometimes we are going to be compromising the overall balance in terms of retaining our strength. |
| 18:55 | Alright, we've completed balancing the big end of our first connecting rod, we've got it on the scales at the moment measuring 379.3. |
| 19:01 | I've already gone ahead and taken my five measurements, again rejected the highest and lowest and we do average out at 379.3. |
| 19:08 | Remembering we are trying to match number three rod so we're actually within a tenth of a gram, a little closer than I was aiming for, but I'm obviously not going to be unhappy with that. |
| 19:18 | And again just to reiterate here, this is an iterative process so take your time, go slowly. |
| 19:23 | This took me three attempts to get the material removed, but it's always easier to remove less material, find that you've still a little bit heavy and then remove more material rather than finding out you've gone too far and then having to reassess the remaining rods. |
| 19:39 | So, at this point we're going to repeat that process for our remaining two connecting rods, number two and number four, trying to match them again to number three. |
| 19:48 | So, let's jump ahead and see what our results look like. |
| 19:51 | At this stage we've completed the balancing of the big ends of the remaining two connecting rods and I first need to address a mistake I just made earlier with my math. |
| 20:00 | Of course, the difference between our heaviest number two and our lightest number three, I said was almost 1.5 grams, but of course basic math was obviously eluding me at that point, clearly that's almost 2.5 grams. |
| 20:11 | And that's the sort of level of imbalance that first of all I'm a little surprised at with the quality set of connecting rods , but also more importantly, I was a little bit concerned as to whether or not I was going to be able to safely remove that amount of material. |
| 20:25 | If we grab this particular rod and we have a look though, we can see I have managed to linish a diagonal across where the rod bolts sit and I've managed to do this without actually reducing the wall thickness, which is the important point. |
| 20:38 | So, at no point is the wall thickness where I've linished less than what the rod manufacturer has actually left on the outside of the rod. |
| 20:46 | So, I'm comfortable that the rod is still not going to be compromised in terms of strength. |
| 20:52 | So, let's now have a look at our results. |
| 20:55 | Our number one, we already know, 379.3, I actually managed to get exactly the same with our number two rod, number three rod obviously unchanged. |
| 21:03 | And interestingly I actually ended up a tenth of a gram below our target with our number four rod , which is another reminder to make sure that you move slowly, taking little amount of material off and measuring your progress consistently. |
| 21:17 | Regardless though, we're well within my target there of half a gram imbalance. |
| 21:22 | So, our big ends are now good to go. |
| 21:25 | We're now going to remove our conrod balancing fixture and now things get a little bit simpler, because we're just looking at the overall weight of the rod. |
| 21:33 | So, let's rearrange things and we can have a look at that. |
| 21:35 | Alright, we're set up now to weigh the conrods overall and what we're going to do is take our connecting rods one at a time and just place them evenly in the centre of our scales. |
| 21:45 | And it is still a good idea just to take a couple of measurements just to ensure that we are in fact getting repeatability, although this is much easier than when we are trying to weigh just the big ends. |
| 21:58 | So, 517.4, let's get the remaining three rods weighed. |
| 22:02 | Alright, so our four connecting rods weighed and again number two is a bit of an outlier. |
| 22:07 | This one has been consistently heavy in both the overall weight and the big end weight. |
| 22:12 | And this time, I've checked my maths, we're 1.5 grams heavier than our lightest, which is number one. |
| 22:20 | I'm very unlikely to be able to remove safely 1.5 grams of material from the pin end so we'll see how close we can get. |
| 22:28 | Again if we can get within half a gram I'd be reasonably happy, but even that might be a touch optimistic , but we'll see how we go. |
| 22:34 | On the other hand, number three, 518.1 grams, I imagine we should be able to reasonably easily get that within spec, remembering I'm looking for half a gram so our lightest there, number one, 517.4 and our number four, 517.5, those two don't need to be touched at all. |
| 22:54 | So, let's head across to the Linisher, we'll start with our number two connecting rod given that that is the heaviest and we'll see how close we can get. |
| 23:03 | Ok, we've completed balancing the small ends of the rods there and despite my concerns as to whether or not I'd be able to remove enough material safely from number two rod, we actually did get that down to 517.7 grams so obviously well within my half gram spec or tolerance that I was looking for. |
| 23:21 | Despite that I've still got plenty of material around the outside of that pin boss. |
| 23:26 | I'm not concerned at all that I've removed excessive material there so that's still going to be nice and reliable. |
| 23:33 | So, at this point we've balanced our pistons, we've balanced our connecting rods, and we can now move onto the next step of our process. |
