Practical Engine Building: Lubrication Related Failures
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Lubrication Related Failures
07.39
| 00:00 | - It's an unfortunate fact of life that if you build enough engines you're eventually going to suffer some kind of failure. |
| 00:06 | With the information contained in this course, your chances of success are going to be greatly increased. |
| 00:12 | However the fact remains that some failures are going to be outside of your control and even the best and most accurately assembled engine in the world can still be reduced to an expensive pile of broken parts if the engine is run low on oil or the tuning isn't right. |
| 00:29 | Particularly if you're pushing the boundaries and starting to target power levels never even considered viable by the factory engineers, failure can be a part of the development process as you find where the weaknesses lie, and then engineer solutions to them. |
| 00:45 | Of course this can be a costly exercise and isn't always viable for those with tight budgets. |
| 00:52 | I'm a firm believer that a failure of any sort is all in vain if we can't learn from the failure, isolate what went wrong, and then ensure that it doesn't happen again in the future. |
| 01:05 | The modules contained in this section of the course will detail some of the most common failure modes I've seen over my career so that you can learn what to look for and how to isolate the cause of a specific engine failure. |
| 01:19 | Possibly one of the most common failures I've seen from performance engines is due to a lack of lubrication to critical engine components. |
| 01:28 | This most often shows up first as moderate to severe damage to the engine bearings, and it can be difficult to correctly diagnose the cause and effect when viewing an engine where the bearings have been so badly damaged that the shells have begun spinning in the journals. |
| 01:45 | Before we get into the actual causes though, it's worth discussing how a bearing problem will become apparent in the first place, or in other words, how to we know when we've got a problem? There are a few clues that will depend on the severity of the bearing issues. |
| 02:03 | If the problem is picked up quickly, then it will be apparent by a gold shimmer in the engine oil. |
| 02:09 | For this reason it's always valuable to inspect the oil at your first oil change. |
| 02:15 | I do this by draining the oil into a large clean pan so that it can be visually inspected. |
| 02:22 | The first oil change can be a little tricky to diagnose though as there will inevitably be some metallic material in the oil from the rings bedding against the cylinder walls, so naturally there may be a shimmer to the oil that will likely be nothing to worry about. |
| 02:40 | What we're looking for is a gold or copper coloured tinge to any material left in the oil, or alternatively any larger pieces of bearing material visible in the oil. |
| 02:53 | If you're concerned at this point then it's a good idea to cut open the oil filter and examine the pleats of the oil filter medium. |
| 03:01 | This is a great place to pick up early bearing issues as there'll be specs of bearing material trapped in the filter medium that are easily visible. |
| 03:11 | If a bearing problem is allowed to continue unabated it's only going to get worse, and what we end up with is the clearance between the bearing and the journal becoming excessive. |
| 03:22 | This leads to the next obvious sign which is an audible knocking sound from the engine, particularly when it's free revved with no load on it. |
| 03:32 | This is particularly noticeable with a conrod big end bearing as it will basically bounce up and down on the crank journal. |
| 03:39 | If you're on the dyno then you're unlikely to hear this knocking sound when you have load applied to the engine however it will become apparent when you back off the throttle and load is removed. |
| 03:52 | Either way it's a sign to immediately stop running the engine and investigate the cause of the noise. |
| 03:59 | Another sign that is often attributed to bearing issues is when the engine is being tuned on the dyno and begins to lose power between runs for no obvious reason. |
| 04:10 | Again this is a sign that there may be a problem and you should stop and address it. |
| 04:15 | Now that we know what signs we're looking for we can discuss what we can expect to see inside the engine. |
| 04:22 | There are however a couple of aspects that can give similar results and it's important to be able to distinguish between them. |
| 04:30 | For example an engine that's assembled with insufficient bearing clearances, may also result in similar bearing damage to what could be expected if there is a lubrication problem. |
| 04:42 | If we've got a lubrication problem that's resulted perhaps from oil surge under high lateral loads, we're likely to see the problem initially show up at the last bearing to receive oil from the oil galleries. |
| 04:55 | This may for example be the big end conrod bearing furthest from the oil pump, so this is the first thing to look for. |
| 05:02 | Is the issue isolated to a single bearing? Are there several bearings showing signs of distress near the end of the main oil gallery? Of course if the oil surge or lack of lubrication remains for a reasonable period of time, then the damage may look relatively consistent across all the bearings, so this does need to be considered too. |
| 05:25 | If the engine continues to run, the damage will become more and more extreme to the point where the bearing shells may be worn so thin that they can spin inside the journal, or alternatively become welded to the crankshaft. |
| 05:40 | Both situations will generally show significant heat discolouration on the parts being affected. |
| 05:47 | Generally you'll see the crankshaft and the bearing cap in question exhibiting a deep blue or black colour from the heat. |
| 05:54 | So the question that can be difficult to answer here becomes, is the damage the result of insufficient clearances on the bearings, or is it a lubrication related issue? While in some instances it may be impossible to definitively say, providing oil pressure is being monitored during initial start up and engine break in, and it's sound, you're likely to see problems from a lack of lubrication become apparent once the engine is being used hard on a racetrack where oil surge is a real possibility. |
| 06:28 | Damage from bearing clearances on the other hand, will become apparent almost immediately when the engine is placed under high load, and this is likely to occur on the dyno during the tuning process. |
| 06:41 | The fix for lubrication problems can be a complex topic as much of this will be specific to a certain engine platform, as well as how the engine is being used. |
| 06:53 | Normal road going cars for example generally struggle to corner at much over about 1G, and this limits the oil movement in the sump. |
| 07:02 | In these applications some attention to the sump design and the addition of baffles to help keep the oil around the pickup in the sump, may suffice. |
| 07:12 | The bigger problem comes from engines that are used in competition cars where lateral G forces of 1.5 to perhaps 2G are not uncommon. |
| 07:23 | Here we enter the realm of dry sump oil systems where an external oil pump scavenges oil from the sump and a high pressure pump draws a constant supply of oil from a remote reservoir. |
