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Engine Building Fundamentals: Engine Break In

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Engine Break In

06.49

00:00 - One of the topics that I see pop up repeatedly is "how should I run in or break in a freshly-built engine?" This is the topic of much debate, and there are generally two polar opposites when it comes to accepted techniques.
00:14 Either the engine is babied, with minimal load and RPM for a break-in period that may extend to several thousand kilometres, or the engine is run hard under full load, almost from the second the engine is first started.
00:29 In this module, I'll discuss my own techniques that I've used successfully to break in hundreds of freshly-built engines with perfect results.
00:38 Before we start though, it's important to understand exactly what we're aiming to do by breaking in a freshly-built engine.
00:46 There's a huge amount of misunderstanding here that we need to clear up, and, as always, if we understand what's going on, we'll have a better idea of how our actions will affect the process.
00:58 Probably the most common myth I hear is that the break-in process is necessary to allow the bearings inside the engine to bed in, and nothing could be further from the truth.
01:09 Remember that the crankshaft is supported in the journals by a film of oil, and we should never have the journal physically contact the bearing material.
01:18 And, in fact, if we do, we're going to have some serious problems that no amount of gentle running is going to fix.
01:26 By far the most important aspect of engine break-in is bedding the new piston rings against the freshly-honed cylinder walls.
01:34 This is particularly critical during the first 20 to 50 kilometres of use, during which the peaks of the fresh hone pattern will be worn down, allowing the rings to properly bed, and achieve a good seal against the bore walls.
01:50 Getting this part right will result in an engine that produces good power, offers minimal blow-by, and minimal oil consumption.
01:59 Get it wrong, on the other hand, and the results will be the exact opposite.
02:03 So now that we know that it's really the ring seal that we're most worried about during the break-in process, we can give some consideration to exactly how we can help achieve this, with the best possible results.
02:16 It's a mistaken belief that the rings seal against the bore due to the radial tension that the rings apply.
02:23 In reality though, this isn't the case, and this radial tension is more important to ensure the rings scrape excess oil off the bore walls.
02:33 The rings actually seal due to the combustion pressure, and during the power stroke, the cylinder pressure acts on the back of the ring, forcing it out against the cylinder wall, and ensuring a good seal.
02:45 When we bed the piston rings we can use this cylinder pressure in our favour to help force the rings against the cylinder wall and promote bedding in.
02:54 This however requires us to apply load to the engine.
02:58 If we simply allow the engine to idle, or run at cruise or low load, the amount of pressure forcing the rings against the cylinder walls is limited, and this can mean that the rough hone pattern will be worn down before the rings are properly bedded.
03:13 If this occurs, then the only solution is to re-hone the block and start again.
03:18 Another common myth is that it's necessary to heat-cycle the engine during break-in.
03:23 I think this comes down to confusion over the term "heat treatment", and a mistaken belief that the engine components are being heat-treated during the break-in process.
03:33 Of course, this isn't the case, and a true heat treatment process requires much higher temperatures than we are ever likely to experience.
03:43 While we obviously need to control and monitor the engine temperature during break-in, heat-cycling is not necessary.
03:51 My personal technique is to apply load to the engine almost as soon as it's started for the first time, and has reached operating temperature.
04:00 This can be done on the dyno or on the road, but either way, the aim is to generate cylinder pressure to make the rings seat as well as possible.
04:09 Of course, during the initial start-up there may be some checks and adjustments necessary, such as checking for leaks, and perhaps setting the ignition timing, but the sooner we can start applying load, the better.
04:22 In fact, absolutely the worst thing you can do with any freshly-built engine is to allow it to idle for extended periods when it's at operating temperature.
04:33 This results in no real pressure on the rings, and an inevitable poor ring seal.
04:39 Now, I'm not advocating that you should jump straight to redline with your foot flat on any new engine, and this can be just as bad as long periods of idling.
04:49 What we want is somewhere in between.
04:52 Since the fresh hone pattern on the cylinder walls will cause a lot of friction as the rings pass over it, this does create a lot of heat, which we need to manage.
05:03 What we want to do is cycle between periods of moderate load, and periods of minimal load.
05:10 When we apply load using the throttle, we get the combustion pressure helping the rings to bed.
05:16 When we back off the throttle and reduce the load, the rings are now allowed to cool back down.
05:21 I'll normally allocate around 30 minutes of running on a dyno to complete the break-in period.
05:27 I'll start by running the engine at approximately a third of the engine rev limit, and using approximately 50% throttle while I'm applying load.
05:37 I'll apply load for around five to ten seconds, and then back off for 20 to 30 seconds, before repeating the process.
05:46 Once the engine has run for approximately 15 minutes, I'll increase the maximum throttle I'm applying to around 75% to further increase the load.
05:56 At this point, the break-in is all but complete, and the engine is ready to be used hard.
06:02 Before moving on to full power tuning, I also recommend performing an oil and filter change, as a lot of debris will make its way into the oil during the bedding in process, and you're also likely to end up with assembly lube, sealant and bore scrapings in the oil, which we want to remove.
06:22 While around 80% of the break-in process will be completed during the first 20 to 50 kilometres of use, the break-in will still continue for some time, so at this early stage I still recommend running the engine on a mineral-based oil.