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Engine Building Fundamentals: Filing Piston Ring End Gaps

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Filing Piston Ring End Gaps


00:00 - Now that you've decided on the ring end gaps you want to run it's time to check and set these end gaps.
00:06 The first step is to unpack your ring set and distribute the rings to each cylinder.
00:12 When we're gapping the rings, we'll be doing so to suit each individual cylinder.
00:17 This allows us to account for any minute variations in the finished bore size and ensures each ring end gap is perfect.
00:26 When you unpack the rings, it's important to make a note of which ring is which.
00:31 Usually, this is quite self-explanatory as the rings will be different thicknesses and hence will only fit into their respective ring groups.
00:40 The ring manufacturer will also often package them separately and note on the packaging which is the top ring and the second ring, for example.
00:49 Now, we need to fit the rings into the cylinders so that we can measure the end gaps as delivered.
00:56 If you've used a torque plate to bore and hone the block, you're also going to want to check the ring end gaps with a torque plate installed.
01:05 Installing the rings into the cylinder is best done by hand by slightly compressing the ring and gently pushing it down into the cylinder.
01:14 We want to make our end gap measurement with the rings located a little way down the bore to give us an accurate measurement.
01:22 And it's also critical to ensure the ring is sitting square in the bore before measuring the gap.
01:28 There are special tools for locating the ring in the bore.
01:32 However, if you don't have one of these tools I find the easiest solution is to use one of the pistons with one of the oil control rings temporarily installed on it.
01:43 You can then press the piston into the cylinder upside down until the oil control ring contacts the deck surface of the block.
01:52 This will locate the ring around about 20 millimetres down the bore and ensure that it's square, ready to be measured.
01:59 Before measuring the end gap, it's a good idea to inspect the gap and see if the ends of the gap are parallel.
02:06 It's common to find that the ends won't initially be parallel and we'll need to do some work to correct this while filing the ring end gap.
02:15 Now we can use a set of feeler blades to check the end gap.
02:19 We want to select a feeler blade that offers just a little resistance as it's pushed through the ring end gap.
02:27 Now we have a starting point for the ring end gap.
02:30 And we know that if the end gap is parallel so we can begin filing the ring.
02:34 When filing the ring, we only want to file one end of the ring, not both.
02:39 When selecting the end to file, you'll typically find that one end is relatively square and the other may be slightly irregular in shape from the manufacturing process.
02:51 The aim is always to achieve a square and parallel end gap so we would choose to file the end that is irregular.
02:59 When filing the rings, it's important to always file the ring from the outside towards the inside to avoid potentially damaging or chipping the inlay coating on the ring face.
03:12 It's also easy to file the ring too far.
03:14 So the key is to make small adjustments and check your progress frequently.
03:20 Once the end gap has reached your desired measurement you can then deburr the ring end with a fine file.
03:27 You can now go through and repeat the process for the remaining rings.
03:31 This can be a slow and laborious job but it's one of the most critical parts of assembling the engine.
03:37 And it needs to be treated with care.

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