Engine Building Fundamentals: Installing Rings on Pistons
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Installing Rings on Pistons
05.37
| 00:00 | - Once the ring end gaps are correctly set and checked it's time to place the rings onto the pistons. |
| 00:06 | There's a few aspects that we need to be careful of when performing this task, and without sufficient care it's quite easy to bend, or break a ring. |
| 00:15 | One of the key aspects we need to understand before going any further is how the rings will be orientated on the piston. |
| 00:23 | Each ring must be located in the correct ring groove with the correct side facing towards the top of the piston. |
| 00:30 | Furthermore though, we also want to align the ring end gaps correctly when we fit the rings onto the piston. |
| 00:37 | The aim here is to to align the ring gaps in a staggered pattern so that there's no direct path for blow-by gases to make it past the rings. |
| 00:46 | While it's always good practise to align the ring gaps, as we'll see shortly, in operation the piston rings will rotate in the ring grooves so they won't remain stationary when the engine is in use. |
| 00:59 | At this point we should already have our ring packs assigned to a particular cylinder, and we should know which is the top ring, and which is the second. |
| 01:08 | Often, the rings will be different in thicknesses, which means they'll only fit in a specific location anyway. |
| 01:14 | However, alternatively, the ring manufacturer may label the rings to avoid any confusion. |
| 01:21 | Let's start by getting the rings facing up the right way. |
| 01:25 | You will notice that the ring will have an identifying mark such as a dot on one face, and this always faces towards the top of the piston. |
| 01:33 | When it comes to the oil control ring, the rails are not marked, and these are symmetrical, which means that they can be fitted in either orientation. |
| 01:42 | The oil control expander, however, should be fitted with the ends facing towards the bottom of the piston, as you can see here. |
| 01:50 | It's also critical, when you fit the oil control expander into the piston, that the ends are butted together properly, and not overlapping. |
| 01:59 | Now that we have our rings in the correct order and facing the correct way, we can go ahead and fit them onto the piston. |
| 02:06 | Before we do this, let's look at the correct alignment for the end gap on each ring. |
| 02:12 | This diagram is a view looking down on the top of the piston, which we can use for reference in any inline or V-configuration engine. |
| 02:21 | We start from the bottom of the piston with the oil control ring expander as the first ring to be installed. |
| 02:28 | This should be installed with the end gap located at approximately 90 degrees as shown. |
| 02:35 | The oil control rails can be installed next, starting with the top rail, and then the bottom rail. |
| 02:42 | Since these rails are very thin, these are quite easy to install by hand. |
| 02:47 | The process I use is to locate the end of the rail in the ring groove, and then gently spiral the rail into location. |
| 02:54 | We want to locate the top oil rail end gap at approximately 240 degrees, and the bottom rail end gap at approximately 300 degrees. |
| 03:05 | It's quite easy to make small adjustments to the final end gap location after the rails are installed, so we don't need to have them perfect right away. |
| 03:14 | Before we move onto the compression rings, we want to confirm that the expander end gap is correctly butted and not overlapping. |
| 03:23 | Now we can fit the second ring, and while it's possible to fit the compression rings by hand, a ring expander is a cheap and worthwhile investment to prevent damage to the rings during installation and removal. |
| 03:36 | This tool gently grabs the ring and expands it so that it can be easily installed over the piston. |
| 03:42 | It also helps to keep the ring flat and straight during installation, again helping to prevent damage. |
| 03:50 | If you're going to install the piston rings by hand, then you want to start by laying the piston ring on the top of the piston. |
| 03:58 | Place a thumb into each side of the ring end gap, and gently expand the ring while holding it flat against the piston with your fingers. |
| 04:06 | This helps reduce the chance of the ring twisting and becoming damaged as it's expanded. |
| 04:13 | Once the ring is expanded far enough to slip over the piston, it can be moved gently down, and located in the ring groove. |
| 04:21 | Regardless whether we're using a ring expander, or fitting the rings by hand, we want to ensure that the rings are only expanded the bare minimum to slip over the piston. |
| 04:31 | Also, be careful not to damage the piston with the ring as it's installed, since the ring is much harder than the alloy of the piston, and the ring ends in particular can be quite sharp. |
| 04:44 | Referring back to our diagram again, we can see that the second ring end gap should be located at approximately 270 degrees, and the top ring end gap should be located at approximately 90 degrees. |
| 04:58 | In some instances where the wrist pin is fitted high on the piston, it may intersect the oil control ring and in this case, your ring set will include an oil control ring support rail, which needs to be fitted on the bottom of the oil control ring groove. |
| 05:14 | These rails provide support where the ring groove has been cut away to allow the wrist pin fitment. |
| 05:21 | The support rail will have an anti-rotation dimple on it, which needs to face downwards, and this should be aligned to intersect with the cutaway in the ring groove, hence preventing the rail from moving in operation. |
