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Engine Building Fundamentals: Component Balancing

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Component Balancing


00:00 - To ensure smooth and reliable engine operation balancing the rotating assembly is a critical step of the engine machining process.
00:09 When I talk about the rotating assembly here I'm talking about the pistons, the con rods, the crank shaft, the front pulleys and harmonic dampener and even the flywheel and clutch assembly or flexplate.
00:22 For the best results, all of these components need to be correctly balanced.
00:28 With some components such as the pistons the balancing process is relatively simple and just requires that each piston weighs the same as the others.
00:38 The process is to find the lightest piston and then remove material from the rest of the pistons to match the lightest one.
00:46 When doing this though we really want to measure the weight of the assembled piston including the rings, wrist pins, and locks.
00:55 Balancing the pistons is typically done using a die grinder to remove material from the underside of the piston in a location that isn't highly stressed such as the outside of the wrist pin boss.
01:08 If you're dealing with aftermarket forged pistons then the weight will normally be quite close already but improvements can still be made.
01:18 Balancing the connecting rods is a little more complex as here we need to focus not just on the overall weight of the rods but the specific weights of the big end and the small ends of each con rod.
01:31 Ideally, we want all of the big end weights to match and all of the small end weights to match.
01:38 And if we can achieve this it also means that the overall weight of each con rod will also be the same.
01:45 Balancing connecting rods like this requires the use of a special fixture that holds the con rod horizontally and allows one end to be supported while the opposite end is weighed on scales.
01:58 The rod can then be removed from the fixture turned around and the opposite end can be weighed.
02:04 When it comes to the crankshaft the balancing approach will depend on the type of engine.
02:10 Inline and horizontally opposed engines are relatively straightforward as the piston and rod weights on the opposing cylinders effectively cancel each other out and hence the crankshaft can be dealt with as a separate entity.
02:25 In this case, the crankshaft is balanced on its own on a special balancing machine and then the flywheel is added and balanced followed by the clutch pressure plate and finally the front pulleys and harmonic dampener.
02:38 This process ensures that each component is individually balanced to zero.
02:44 And this means that at a later date a different flywheel or clutch could be fitted simply by balancing that particular component without the need to disassemble the engine and rebalance the crankshaft.
02:57 If you're dealing with an engine that uses a V configuration then the balancing process is a little more complex.
03:04 And this time the weight of the pistons and the con rod assembly needs to be taken into account during the balancing process.
03:13 What the machinist needs to do here is separate the weight of the con rod and piston assembly into rotating weight which is the weight that rotates with the crankshaft and reciprocating weight which is the weight that moves up and down.
03:28 In this case, a calculation is made based on the piston and rod weights to calculate what's known as a bob weight.
03:36 This bob weight is represented by a physical mass that's attached to the crankshaft journals during the balancing process.
03:45 For our purposes, it's not necessary to understand how the bob weight is calculated or how the crankshaft is physically balanced as this is the engine machinist's task to perform.
03:57 When the crankshaft is balanced this may require material to be removed from the counterweights.
04:03 However, in some V-configuration engines weight may actually need to be added back into the crankshaft.
04:10 This might sound a little difficult to achieve however it can be done by adding slugs of heavy metal to holes that are drilled horizontally through the crankshaft counterweights.
04:21 Heavy metal such as Mallory is a material with a higher density than the base material of the crankshaft.
04:28 And hence replacing some of the crankshaft material with heavy metal increases the weight.

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