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Engine Building Fundamentals: Line Boring / Line Honing

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Line Boring / Line Honing


00:00 - Now we're going to move on and discuss a couple of machining processes that may be applied to the main bearing journals in the engine block.
00:08 These are corrective processes and they're know as line boring and line honing.
00:13 The actual process that's used will depend on how bad the alignment is initially and hence how much material needs to be removed to correct this.
00:23 These processes may also be referred to as align boring and align honing but essentially these terms all refer to machining processes used to correct alignment and sizing issues with the main bearing journals or main bearing tunnel as it's also referred to.
00:41 The alignment of the crankshaft main bearing journals in the engine block is critical to the reliability of the engine particularly with regard to the bearing life itself.
00:52 It can also affect the frictional losses inside the engine and hence affect the amount of power the engine produces.
00:59 It's easy to assume that the main bearing journals are all perfectly aligned, concentric and on the correct size.
01:07 However in reality this main not be the case.
01:12 OE production tolerances and manufacturing techniques alone may mean that the journal alignment and size isn't perfect.
01:19 However if you're fitting aftermarket studs to help clamp the main bearing caps to the cylinder block, these may distort the block or the caps and hence affect the journal alignment or size.
01:33 The other aspect to consider is the alignment of the main bearing journals with regard to the deck surface, sump rails and the cylinders themselves.
01:43 In an ideal world the crankshaft centre line will be perfectly parallel with both the sump rails and the deck surface.
01:50 And each cylinder would be perpendicular to the crankshaft centre line.
01:55 In many cases, some corrective machining will be required to achieve this sort of alignment.
02:02 In some cases the factory main bearing caps may have a known weakness when a certain power level is exceeded.
02:08 And in these engines it's often common practise to replace the factory bearing caps with either billet caps that are much stronger or perhaps swap from factory two bolt caps to four bolt caps which are clamped more firmly into the block.
02:24 In this case the new caps will need to be machined to achieve the correct size and alignment.
02:31 The process of correcting journal size and alignment begins by taking the main bearing caps or girdle and removing a small amount of material from the mating faces where they contact the block.
02:44 Naturally this will end up reducing the size of the main bearing tunnel.
02:48 And this is essential because it now allows the boring bar to remove excess material and get the alignment and size to whatever is required.
02:58 Depending how bad the alignment is initially and hence how much material needs to be removed, will affect which process is applied for the machining.
03:07 If a minor correction is necessary then this may be achieved using a hone, however major corrections will require boring followed by honing to provide the correct surface finish.
03:20 If you're dealing with modern engine blocks often the dimensional accuracy of the factory machining will be good enough that this sort of corrective work won't be required so it's certainly not a task that needs to be applied to every engine unless you're specifically making changes such as fitting aftermarket bearing caps.
03:41 A good example of where align honing is necessary would be in a Subaru engine block when a set of aftermarket studs are used to bolt the two halves of the block together.
03:53 The nature of the alloy block coupled with the higher clamp offered by stronger fasteners, can result in minor distortion of the main bearing tunnel when the fasteners are tightened.