Running In


By Kevin Ash

Pictures: Castrol, press various

(click on images for full size)
So should you? Or shouldn’t you? The brand new bike parked outside is gleaming. You’ve just polished it for the third time today, it looks gorgeous in the sun and seeing as you’ve spent the biggest part of nine grand buying it, naturally you want to look after it as best you can. You’ll get it serviced, keep it clean, lock it up... but how about the engine? This is possibly the single most complex and finely made mechanical device you will ever buy, it’s by far the most expensive component on your bike, and you not only want it to last, you want it to perform to its full potential.

Running_in_02Do they have feelings and suffer when you're cruel?So should you run it in? And just as important, how? Ask ten mates and you’ll get ten answers, then another five from your dealer, the manufacturer, a workshop mechanic, a magazine helpline and the back of a special running-in oil container. For once, and at last, we have the definitive answer, which includes how to do it and for how long, but first we’ll justify how we arrive at that by taking a look at what really happens when you run a brand new engine in the early stages of its life.

Running_in_08If your bike's a little older then it still needs a long running in period. This one's almost doneIt’s worth bearing in mind that we’ll be talking only about modern liquid-cooled four-stroke engines – for new Royal Enfields, rebuilt RD400 Yamahas and anything more than ten years old with new parts, this doesn’t apply, although the information will help.

The first myth to debunk is that modern engines don’t need running in at all, although there’s a twist: with many bikes (depending on capacity) running them normally with few concessions to their newness will run them in just fine. At which point it will help to know exactly what running in means....

There are two main processes which take place when a new engine is run in, called conformability and surface finishing, and two main areas where these can apply. Conforming describes the shape changing which occurs as components wear to fit each other better, while surface finishing is about the alterations at a microscopic level which happen where moving surfaces pass over each other. Modern plain bearings such as you get in crankshaft journals, big ends and small ends are manufactured with sufficient accuracy that no conforming takes place, and so it shouldn’t as they’re separated by a film of oil.

Running_in_05Pistons suffer from heat, stress, abrasion, distortion. And you thought you had it tough...Also, they don’t suffer significant distortion through heat or load. So the only change that will occur in the early stages of their lives is to their surfaces, which initially are machined. However smooth they feel to the touch, seen through a microscope they’re uniformly rough and jagged, like a micro version of the Alps, and the highest peaks can poke through the film of oil which ought to separate the bearing surfaces. Take it relatively easy with the engine and the tops of those peaks will be gently tapped off – over do it and they’ll be clouted hard and take large lumps of the rest of the surface with them.

Pistons and cylinders are more complicated. They have to deal with higher loads, live in an environment with large heat gradients and the most extreme temperatures, and the intricate shape of pistons means they distort in a complex fashion as they heat up. Similar changes to the surface finish take place on piston and bore surfaces, with additional lubrication considerations, and in addition, there is initial piston and bore wear which conforms the shapes of these two components more closely to each other.

Running_in_13Guzzi's engines were the first bike engines to have all-aluminium cylinders with Nikasil bore coatingsOne important aim, more so than in plain bearings, is to modify the piston and bore surfaces from the initial machined and jagged finish to one with a combination of plateaus and valleys. The plateaus perform the task of bearing the loads, which between a piston and bore can be very high, while the valleys serve as reservoirs for retaining oil, which not only reduces friction, it also helps with heat dissipation. The ratio of plateaus to valleys is important: too many valleys and excess oil will be retained on the surface, which in turn will prevent the engine from running in properly and increase oil consumption. A too-gentle life prevents plateau formation. Too much plateau however and the combination of increased surface area with reduced oil will mean higher friction, in turn causing more wear, more heat generation and reduced power. This can come from being too hard with a new engine, when you’re polishing the surfaces too carefully, although other factors come into play which make life less simple than this. For example, on a lightly used new engine the bores become coated with a lacquer which stops further running in and surface modification, leaving you with high oil consumption and poor ring sealing, while in a hard usage engine you can find deep scores and even minor ‘picking up’ in the bores, where the piston material is smeared and damaged.

Running_in_15You have to be trying hard to damage a modern road bike engineYou’ll struggle to do this on a road bike used on the road though. Sophisticated modern finishing techniques during manufacture do much of the job of running in for you – bores are first ‘plateau honed’ then fine finished, resulting in a surface not too far from a properly run in one, although there’s still room for improvement.

Conformability used to be the most directly obvious factor in running in – get it wrong and pistons would seize. The problem is that a piston is heated strongly from the top only, as well as having a fairly complex shape, so when it expands it changes from an easy round shape into a distorted version with high points that can squeeze up too closely to the bore. But modern computer aided design with its finite element analysis techniques can predict very accurately how a piston will distort in use, so much so that in practice it can be designed ‘distorted’ to start with so it becomes round and even as it heats up. It’s not quite perfect and with manufacturing tolerances thrown in you do still benefit from conforming the piston to the bore by running it in, which in this case means wearing it until the high spots, small as they are, rub down.

Nikasil and similar bore coatings help here too. These consist of very hard silicon carbide particles suspended in a softer aluminium matrix, which is easily conformed. (See correction by R F Wilson in comments below). Water cooling is also on your side, as this reduces heat unevenness and distortion with it.

Running_in_06If this was a two-stroke he'd keep one hand on the clutch at all timesThe worst case is an air-cooled two-stroke, which not only has hot and cold gas running up its sides as well as the combustion chamber heat, the cylinder is full of holes which increase piston loads and distort horribly with heat. No wonder two-stroke racers always ride with one hand over the clutch...

So, your engine will survive if you thrash it from the outset, but are there other consequences? By conforming the pistons quickly you will increase the power output faster than an engine being run in, but the component surfaces won’t stabilise, at least not until you start to use the engine less hard and the running in process can begin. This will mean higher friction, so the engine’s potential peak power won’t be realised, and oil consumption will be higher too (although modern engines use so little in the first place you might not even notice). You’re unlikely too to notice the loss of a few bhp on a big sports bike, but you won’t, as many an anecdote would have it, be getting the best out of your engine, which if nothing else will bother the mechanically sensitive.

Don’t worry though if you’ve had to thrash your engine initially because some gormless oik in a souped up Astra keeps trying it on at same set of lights every evening – you can restart the running in process to repair and stabilise the surfaces later. In fact, once an engine’s properly run in, its running in history doesn’t affect its peak power.

Running_in_14All her careful work then you spoil it by not running it in properlyBut it does increase its power as it’s run in, and continues to do so for the first 1000 to 5000 miles as all the surfaces stabilise and conforming is completed – loosening up, most people call it, as the internal friction reduces noticeably in this period. An engine wears very little for most of its life though, with wear happening most rapidly in the first 500 miles, then right at the end of the engine’s life, just before it finally goes bang or grinds to a halt.

Running_in_03Why go easy on your engine when it was red-lined only ten feet from the end of the production line?It is true though, as many riders suggest, that you can be too gentle with an engine. Use it too lightly and the moving surfaces won’t generate enough heat to alter their composition, with the bore lacquering problem mentioned earlier hindering things even more. The engine simply won’t wear enough to conform its components or stabilise its surfaces and will remain in an odd as new condition for all its life, during which time it will wear faster and use more oil. Also, because its internal friction will be higher and the piston rings won’t have conformed or had their surfaces stabilised, there will be increased blow by, where cylinder pressure is lost to the crankcase past the rings, and power will be down compared with a run in engine.

* How to run in an engine

Running_in_07Don't overload your engine at low revsHandbooks, as in most things, play safe in telling you how to run in an engine, usually suggesting 1,000 miles (1,600km) or more. But for once this can do more harm than good. According to Peter Brett from the world leading Castrol Technology Centre in Pangbourne in south east England, 500 miles (800 km) is about right for a modern bike engine. “Running in now is more about cleaning up the manufacturing and stabilising the surfaces, which means taking it a bit easy for the first 500 miles,” he says. “Not too easy though! In practice, this just means riding normally. The worst thing you can do is load an engine at low revs, and avoid very high revs at first. Build up gradually and don’t suddenly give it full power as you pass the 500 mile mark after being gentle!”

There’s very little a owner can do to find out if his engine is running in properly – Castrol measures blow by, the gas escaping past the piston rings, but even this on many modern engines is minimal from new. You could always send off your pistons for a microscopic examination, but this isn’t very practical... And as mentioned, oil consumption will rarely be noticeably different, even if it halves as you run in.

Running_in_12Try to keep your engine cool while it's running inBut do keep an eye on the temperature gauge. A new engine runs hotter because of its higher friction, and if the needle starts to rise above normal, back off the throttle or if it’s hot because you’re in traffic, stop for a while to let it cool. Although liquid cooling and the electric fan will prevent real overheating, even so you’ll get higher than ideal localised temperatures which can interfere with running in.

Don’t mollycoddle your new engine with expensive oils either. Running in oils are rare and completely unnecessary on a modern engine, but here’s a shock, don’t splash out either on a costly fully synthetic oil until your engine’s covered at least 5,000 miles (8,000km). This comes from the highest authority, Castrol, who would love you to buy the company’s expensive synthetic oils...

Running_in_17This is why the Castrol boys know what they're talking aboutPeter Brett says that they’ve discovered synthetic oils actually interfere with running in, for reasons which go beyond their low friction properties - there also seems to be a chemical process happening which hinders it. “Although you can treat an engine as fully run in after 500 miles, surface stabilisation continues for at least the first 5,000 miles of an engine’s life,” he says. “Synthetic oils actively prevent this from happening, and not simply by holding friction surfaces apart, although we still don’t know exactly why and how this happens. But there’s no doubt they inhibit the process itself. So the consequence of using a synthetic too early is your engine will never run in properly. I would even suggest waiting until 10,000 miles (16,000km) before using it in most engines subjected to normal use. Until then, you’re best to use an inexpensive but branded mineral oil.”

So, save money by using a cheaper oil when your engine is new, it will run in properly and you will improve its longevity, power output and oil consumption. Can’t be bad, and that comes from people whose interest is in selling you expensive synthetics.

It’s worth noting that when you do reach the mileage where a synthetic will start to be of benefit, only use a fully synthetic if it’s specifically designed for motorcycles with wet clutches (unless your bike has a dry clutch anyway, eg Ducati, BMW, Guzzi) or you’ll suffer clutch slip. Otherwise go for a semi-synthetic, but even then check it’s suited to wet clutch systems.

* Coat of iron

Running_in_16Dull grey coating on the pistons is a ferrous solid lubricant, and it won't look like this for longThe irony with modern engines being so resistant to early abuse is that many, if they’re stripped down after a few miles, look like they’ve run 50,000 miles (80,000km) on old sump oil. More specifically, the pistons on many bikes can look badly scratched and scored even after a gentle first 500 miles. Don’t worry mister, they all do that...

The reason is a relatively new idea of adding a ferrous coating to pistons (ferrous being iron, but it doesn’t sound as trick...) partly because it acts as a solid lubricant, reducing friction. In addition, it separates the rest of the piston from the bore, which is very helpful because when similar materials rub against each other they are much more likely to pick up and scuff than two different materials. Pistons are made of aluminium which also happens to be the base matrix material for bore linings such as Nikasil, so separating the two with a thin layer of iron reduces the chances of pieces of aluminium from one being picked up by the other.

The iron coating though is soft, and in the early stages of an engine’s life, small pieces of very hard silicon carbide are knocked off the bore walls. These then leave score marks on the piston’s surface, giving the impression it’s already wearing badly. It’s not, and the scratches have no effect on performance, oil consumption or anything else.

Joined: 01/05/2009


Thanks for putting this together, there is some very useful information here.

"Proper" engine break-in has been a topic i have long sought to increase my knowledge of. I think this is a great article, but it does leave me with one resounding question. While warranty issues explain why manufacturers recommend a gentle break in, there seems to be no explanation as to why almost all factory fill oils in performance engines are full synthetics. Oil companies recommend petroleum oils, engine builders generally say the same, but OEMs usually opt for Castrol or Mobil 1 synthetic (which aren't really considered synthetics by purists, as they are group III based). Any thoughts as to why this might be?

steven.hood7's picture
Joined: 20/08/2009

This running-in article is the best and most comprehensive explanation of what happens within an engine during the first 500 miles +.Will point some friends to your Technical lists.Thanks again Kevin and i will post again when i get to the bottom of the Trip/Odometer saga on my Fireblade RR8.

Joined: 03/10/2010

Just a correction on the composition of Nikasil. Nikasil and its competitor Galnikal are not particles of silicon carbide in an aluminum matrix. They are particles of silicon carbide (about 5% by weight) in a NICKEL matrix (hence the name Nikasil). Nikasil is a patented process of Mahle Kolbenfabrik.

Iron coated pistons are not used in Nikasil plated cylinders. Rather, iron coated pistons are used with cylinders made with the Reynolds process, where the block is cast from an aluminum alloy with up to 25% silicon. After the cylinders are bored, the aluminum is etched back very slightly, leaving hard crystals of silicon as a wear surface. Iron coating the pistons eliminates the galling that might otherwise occur between similar aluminum surfaces of the piston and the aluminum matrix in the cylinders.

kevash's picture
Joined: 05/10/2008

Thanks for the corrections, I'll pass those on to my sources at the bike factories and make a reference to this comment in the main text above.

But I'm keeping the English spelling of aluminium!

Joined: 19/08/2010

Fascinating reading. Quite agree with the ten different people with 10 different opinions on this. As a former bike instructor and new owner of a vfr800 vtec i kind of lean with the 'ride as normal' brigade.

When i was teaching, we used to use CG 125's and CB 500's and from the word go these poor bikes lived a battered existence. That said running in was a difficult process as everything got abused from the off. Surprisingly after about 5k miles, all of these bikes, despite the obvious dents and scratches had surprisingly good engines that ran like clockwork and never gave us any nonsense.

As to my 800, a quick trip abroad tends to do the business for me, i mean 6500rpm which i'm not supposed to pass for the first 500 miles or so, takes me into the 80mph range which is fine across the water and imho does the bike no harm at all. I must have run in dozens of bikes over the years, never cotton wooled them during the running in period, and also never had any problems either. Not saying this is how to do it either, but works for me.

Joined: 08/09/2009

i have many times given advice or mentioned to new owners about the importance of running in and am thankful for this article as years ago when i started life as a bike mechanic. My memories of one customer who did not hear all the advice of run under 5k for the first 500 miles then gradually take up the revs to reach 1000 miles and do not labor. He ran his bike under 5k for a thousand miles and then found it would not go over 5k. A quick road test found the revs in lower gears easy to get over but in top gear a bit hesitant....
With the knowledge on oil maybe my Ducati 916 is up to 32k now so maybe i might treat it to some fully sythentic....