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Practical Engine Building: Engine Break In

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Engine Break In


00:00 - One of the topics I see pop up frequently is how should I run or break in my freshly built engine? This is a topic of much debate, and there are generally two polar opposites when it comes to accepted techniques.
00:13 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.
00:26 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.
00:35 Before we start though it's important to understand exactly what we're aiming to do by breaking in a freshly built engine.
00:43 There's a huge amount of misunderstanding here that we need to clear up.
00:47 And as always if we understand what's going on, we'll have a better idea of how our actions will affect the process.
00:56 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.
01:07 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.
01:17 And in fact if we do, we're going to have some serious problems that no amount of gentle running is going to fix.
01:25 By far the most important aspect of the engine break in is bedding the new piston rings against the freshly honed cylinder walls.
01:33 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 cylinder walls.
01:47 Getting this part right will result in an engine that produces good power, offers minimal blow by, and minimal oil consumption.
01:56 Get it wrong on the other hand, and the results will be the exact opposite.
02:00 So now that we know that it's really the ring seal that we're worried about most during the break in process, we can give some consideration to exactly how we can achieve this with the best possible results.
02:12 It's a mistaken belief that the rings seal against the cylinder walls due to the radial tension that the rings apply.
02:19 In reality though this isn't the case, and this radial tension is actually more important to ensure that the rings scrape excess oil off the cylinder walls.
02:30 The rings actually seal due to the combustion pressure itself, and during the power stroke, the cylinder pressure acts on the back of the ring forcing it out against the cylinder wall, and hence ensuring a good seal.
02:44 When we bed the piston rings, we can use this cylinder pressure in our favour to help force the rings against the cylinder wall to promote the bedding in process.
02:54 This however requires us to apply load to the engine.
02:59 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 completely bedded.
03:14 If this occurs then the only solution is to rehone the block.
03:19 Another common myth is that it's necessary to heat cycle the engine during break in.
03:25 I think this comes down to a confusion over the term heat treatment, and a mistaken belief that the engine components are being heat treated during the break in period.
03:36 Of course this isn't the case, and a true heat treatment process requires much higher temperatures than we're ever likely to experience in normal operating conditions.
03:46 While we obviously need to control and monitor the engine temperature during break in, heat cycling is not necessary.
03:55 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.
04:04 This can be done on the dyno or on the road, but either way the aim is to generate cylinder pressure to make sure the rings seat as well as possible.
04:14 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, as we've previously discussed.
04:25 But the sooner we can start applying load the better.
04:29 In fact absolutely the worst thing you can do with any freshly built engine is allow it to idle for extended periods when it's at operating temperature.
04:38 The result is no real pressure on the rings, and an inevitable poor ring seal.
04:44 Now I'm not advocating that you should jump straight to the red line with your foot flat on any new engine, and this can be just as bad as long periods of idling.
04:53 What we want is somewhere in between.
04:56 Since the fresh hone pattern on the cylinder walls will cause a lot of friction as the rings pass over it, this generates a lot of heat which we'll need to manage.
05:06 What we want to do is cycle between periods of moderate load and periods of minimal load.
05:13 When we apply load using the throttle, we get the combustion pressure helping the rings to bed.
05:18 When we back off the throttle and reduce the load, the rings are allowed to cool back down.
05:24 I'll normally allocate around 30 minutes of running on a dyno to complete the break in period.
05:30 I'll start by running the engine at approximately a third of the engine rev limit, and use approximately 50% throttle when I'm applying load.
05:40 I'll apply load for around five to 10 seconds and then back off for 20 to 30 seconds before repeating the process.
05:48 Once the engine has been run for approximately 15 minutes, I'll increase the maximum throttle I'm applying to 60% to 75% to increase the load further.
06:00 At this point the break in is all but complete, and the engine is ready to be used hard.
06:05 Before moving onto 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 likely to end up with assembly lubricant and sealant, as well as scrapings from the cylinder walls in the oil and we want to remove this.
06:26 While around 80% of the break in process will be completed during that 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.
06:43 If you plan on swapping to a full synthetic, I'd wait until the engine has completed around 200 kilometres of use first.
06:51 If you're running an engine that uses a flat tappet style lifter, then some special precautions are necessary here.
06:58 Most camshaft manufacturers will offer their own advice for break in of the cam and lifters, and if this isn't adhered to then the cam and lifter may end up badly worn.
07:09 The process actually doesn't deviate much from what I've already recommended.
07:14 In particular it's important to make sure that the engine isn't allowed to idle for the first 15 to 20 minutes of use.
07:22 Beyond this we also want to make sure that the engine RPM is constantly varied up and down, from around 1500 to 2000 RPM, up to 3000 to 3500 RPM.
07:34 You can either incorporate this into your break in process on the dyno, or alternatively follow the cam break in process first.
07:44 If you're going to break in the cam before driving the engine, then I'd recommend using quite large throttle openings when you're revving the engine.