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Practical Engine Building: Step 5: Balancing Parts

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Step 5: Balancing Parts


00:00 - During the engine machining process, we had the crankshaft and the rotating components attached to the crankshaft balanced.
00:06 However now we're going to consider the connecting rods and the piston set.
00:11 Now the connecting rods that we're using for this particular engine build are a set of Carrillo conrods.
00:16 These are a relatively high end product, and we've already gone through and checked the big end and small end weights of the Carrillo conrods and they're all within our tolerance so we're not going to go any further with the balancing during this particular step.
00:31 What we are going to look at however is the balance with the CP pistons.
00:35 And this is going to be quite a good lesson because these pistons have actually been balanced during the machining process as well.
00:43 So it's always a good idea just to double check everything that we see when we get our components back from machining and the balance on these pistons is no different.
00:53 So we've got all of the components laid out here, we've got our digital scales and we're going to go through and get a baseline measurement for everything.
01:01 What I'm going to do is start by just checking the weight of the ring packs and also the pin locks.
01:09 Generally these are components we can disregard.
01:12 They're almost always within very very close tolerance to each other, but of course we don't want to take any chances so we're going to double check that now.
01:21 So I'm just going to check two of the ring packs and we'll check two pairs of the pin locks as well.
01:27 Let's start with our ring packs.
01:34 So we can see our first ring pack there weighs 20.60 grams.
01:38 We'll just try our second ring pack and see if that's the same.
01:46 And you can see that we're exactly the same there, 20.60 grams.
01:50 We'll repeat that process for our pins locks.
01:54 Place two on the scales now, 'cause we're using two per piston.
01:58 You can see those weight 1.95 grams.
02:02 And we'll just try another pair here as well.
02:08 And see we actually have a difference there but it's only two hundredths of a gram.
02:12 So this is just to demonstrate that in this case we can disregard the weight of all of these components.
02:17 Of course we would go through and check all of the components, all of the ring packs, and all of the pin locks, however for our demonstration today we can see that they all weigh exactly the same, or close enough to that we can disregard them, so we can concentrate our balancing efforts on the pistons and the wrist pins.
02:35 So what we're going to do now is go through and weigh each of the pistons, and then each of the wrist pins, so we can get our starting point.
03:25 So we've got our base weights for our pistons set there, now remember these have already been balanced by our engine machinist, and what we can see over the first five pistons, everything's looking really good there.
03:36 We've got a mass that varies from 337.01 grams, through to a heaviest of 337.06 Now I'll point out here I am measuring down to two decimal places or a hundredth of a gram, however what we're going to be doing here is rounding and really what we're looking for is to get our piston weights matched to within a tenth of a gram.
04:02 So at the moment I'm just adding a little bit of precision, we'll be removing that later and averaging everything or rounding everything I should say.
04:10 The concerning part there though is if we look at our piston number six we can see that that is quite a bit lighter, almost half a gram lighter at 336.55 grams.
04:22 So there is still some work to do with our piston set and this is again why it's important to double check everything when we get our components back from the machining.
04:33 Let's go through and have a look now at the weight of the wrist pins and hopefully we're going to be able to use the wrist pins and move them around within the piston set to help get the overall balance a little bit closer before we have to start removing material.
05:30 Ok so we've finished weighing our wrist pins there and we can see that we have a lightest wrist pin at 137.26 grams, and our heaviest wrist pin is 137.49 So quite a large variance on a machined component like that.
05:47 But we can use some of this to our advantage here.
05:50 So what we're going to do is place the wrist pin number one along with our lightest piston which is piston number six, and that's going to help bring up that overall weight.
06:00 So what I'm going to do now is we're just going to mix and match these wrist pins with the pistons and try and get that set a little bit closer, then we'll have a look at our overall weights.
06:18 Alright so we can't really achieve too much here, the aim really is to just try and bring up that weight of our lightest piston, and hopefully that's going to mean that we're not trying to remove so much material from the other pistons.
06:31 We've got our set matched now, so we're going to go through.
06:35 Obviously we could just add up the individual weights, but it's as easy now just to weigh the piston, and the wrist pin as a matched set.
06:44 Let's go through and do that now.
07:08 OK so we've completed our second weighing now with our pistons and our wrist pins as a matched set.
07:15 We can see that we have a heaviest which is piston number one at 474.46 grams, and we have our lightest, number six, at 474.05 So if we round these to one decimal place or a tenth of a gram, we'd be 474.5 at our heaviest and 474.1 as our lightest.
07:36 So we now have a maximum of four tenths of a gram that we need to remove from our heaviest piston.
07:43 We're going to go through now and remove some weight from the heavier pistons until we get them to match our lightest piston.
07:50 So let's have a look at that process now.
08:43 So we've gone through and removed a little bit of material from our first piston.
08:47 Now when we are doing this process we want to make very small adjustments and frequently check our progress.
08:53 It's always easier to make more adjustments and remove more material than find out that we've gone too far.
09:00 So remember with our first piston we were trying to remove four tenths of a gram, and we started with a mass of 337.0 grams, so let's check and see where we're at now.
09:17 So we can see at the moment we're sitting at 336.7 grams so we've removed three tenths of a gram so far, we've got another tenth of a gram to go.
09:26 So I'm going to continue the process, then we'll move on and complete the rest of the pistons.
09:31 Now it is important as well when we are removing material from the pistons to understand where we want to remove that material.
09:39 And generally in a forged piston such as this, what we're wanting to do is remove material from the inside of the wrist pin boss and this is an area where we're going to be removing material without actually reducing the structural integrity or the strength of the piston.
09:56 OK let's continue with our balancing now.
10:51 So at this point we've gone through and we've made some adjustments to our piston weights, we're going to now make one final measurement of our piston and our wrist pins together and make sure we are within a tenth of a gram.
11:20 So there's our completed piston and wrist pin weights.
11:23 And we can see that our heaviest measures 474.10 and our lightest is 474.02 Again just to reiterate while I have measured here down to a hundredth of a gram, it's not necessary to be that accurate.
11:39 All we're trying to do is match the weights to within a tenth of a gram.
11:43 So at this point our pistons are balanced, let's move on with the next step of our process.

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