Why do you need to ‘run in’ your engine?
Got a new bike? Then you’ll have seen that wee sticker on the tank telling you to keep the revs down for the first fifteen hundred kilometres or so. Delve into the owner’s manual, and you’ll get more details on what they want from you. Basically, they’re asking you not to leap on this zero-kilometre machine, hit the limiter from cold, and travel the first half kilometre with the rear tyre spinning through the first three gears…
Words by Alan Dowds
Why though? And what happens if you don’t bother?
We’ve asked race techs, frontline mechanics, engine builders, oil boffins and bike firms what the score is, and their answers are pretty interesting. Because there’s a lot of BS out there about this area of bike life. Guys in bars up and down the land are full of advice on how to treat a brand new bike. ‘Thrash it from cold’, they’ll opine, swigging from a pint of Kingfisher. ‘Opens up the clearances, stops the bores glazing, makes a load more power.’ Meanwhile, your mate Cautious Dave is panicking that you’ll blow up your new wheels. ‘Go really steady,’ he offers. ‘Keep it under 5,000rpm for 800 kilometres, or it’ll burn oil, lose compression, and make 20bhp less than it should.’ As ever, the truth probably lies somewhere in between these two extremes. But why do we need to ‘run in’ an engine at all?
Firing up a spanking new bike
Well, let’s have a look at what happens when a bike engine starts for the very first time. If you could shrink yourself down like in that film Fantastic Voyage, and float about inside your Gixer motor in a microscopic submarine, what would you see? Boom. Our motor’s fired up for the very first time. An eight hundred degree flame fills each combustion chamber in turn, pushing down on the piston and stirring the crankshaft from rest. Assembly lube is being boiled and burned away from the cylinder walls, and the piston rings are blown out against the cylinder walls, sealing off the combustion gases, while getting dragged up and down the freshly-manufactured cylinder surfaces.
Understanding the mechanics
The oil pump has built up pressure fast though – and is squirting cool, clean, fresh multi-grade all around the bores. Down below, that same oil has built up a pressurised layer round the plain crankshaft bearings, keeping the con-rod big ends at the proper clearance, and letting the crank spin true in the cases, with minimal friction. Our motor settles down to a fast idle, and the valve spring retainers push down further into their collets, as the springs settle, and the valve sealing faces hammer into their seats fifteen times a second; the beginning of a very tough relationship…
That’s how most bike engines start their life – usually at the end of the assembly line at the factory. A new bike will get at least a run up and down through the gearbox, in order to make sure everything works – it would be silly to ship a bike halfway across the world, only to find out someone left out sixth gear…But that two-minute factory run won’t do much running in, so it’s down to you and your wheels. What’s going on? The main point of running-in is, essentially, to get all the parts to bed in together nicely. Some parts don’t need much of this – ball bearings and plain crankshaft bearings are very accurately matched to start with in terms of size and clearance, and they’ll have a pressurised oil supply to keep them sweet.
But the pistons, piston rings and cylinder bores are a different matter
Firstly, they’re moving in a different way, sweeping up and down over a very large area of metal, and while this has been very carefully manufactured, it will still vary in dimensions and clearances. The piston rings also have to make a gas-tight seal against the bore, so there’s little room for error here. Any gaps will let super-hot combustion gases jet past, losing power, wearing piston and bore walls, and polluting the oil. A tiny amount of blow-past is normal, and the motor can deal with this, but too much is bad news.
So the pistons, rings and bores need to ‘wear in’ to each other geometrically, gradually altering their shape to perfectly match each other. But there are also some microscopic changes taking place too. The bore surface needs to be able to hold some lubricating engine oil to keep the pistons and rings from seizing. A perfectly smooth mirror-surface wouldn’t do that – the oil would just run off, so we need a slightly rougher surface – but not so rough that it causes wear and friction. Talk about being fussy, eh!
When the cylinders are made, they’re given a ‘honed’ finish, which looks like cross-hatching. This puts thousands of tiny ‘scores’ on the surface, giving lots of tiny valleys for oil to sit in. Now, as we run the engine in, we want the ‘high-points’ in the surface to smooth down, while still leaving the little valleys that can store tiny reservoirs of oil. Then, as the rings sweep up and down, they get loads of little dabs of lube, helping them wear to a suitable clearance – and then keeping wear very low. Once the motor’s been properly run-in, the bores, pistons and rings should maintain the proper compression pressure inside the combustion chamber, while keeping frictional losses low, and with very minimal wear, over tens of thousands of kilometres.
What the pros say…
What do we need to do then? Well, most mechanics and techs we spoke to talked about ‘load’ rather than just simple revs. Simon Green, veteran BSB crew chief explained: “The most important thing about running an engine in is to keep the ‘load’ low, not necessarily the rpm. You can spin a brand new engine up to 9,000-10,000rpm in neutral and it’ll not harm it. But asking it to pull 3,000rpm in top on 100% throttle will.” So, you want to keep throttle openings low where you can, and use the gearbox lots to keep the engine spinning around the midrange, and avoid bogging down at low revs with big throttle openings.
You can be too gentle though. Simon says: “Avoid constant light load rpm. This induces some harmonics in the internals which can lead to abnormal patterns on bearings etc. and glazing in the bores, which reduces the ring sealing. Lastly, (and there is some debate on this point!) don’t run your engine in on the best oil you can get. In effect you are delaying the bedding in process, as it needs a little wear to settle in.”
The best type of ‘running-in’ oil also raises a debate here
Most of the engine builders we spoke to recommended using a cheaper, basic mineral oil while running-in, on the basis that it will let the engine parts wear against each other faster. For most new bikes though, people will be using the oil it comes with. Kawasaki reckons it doesn’t use anything special for running in – the firm’s European PR manager Martin Lambert told us: “Special oil for running in? No. It’s hardly in there long enough before first service.”
Meanwhile, KTM does use a special oil in its new engines
The firm’s Simon Roots (who??!!) told us: “A running-in oil is used during this period, which is then swapped for Motorex oil, recommended at 1,000km as defined in the service schedule.” We also spoke to Martin Wabnegger of Swiss oil firm Motorex, which supplies KTM with its lube. He gave us some insight into these running-in oils. “The bedding-in happens via plastic deformation of the surface roughness, through the heat created by the friction between two moving surfaces. In order to allow for this friction to create the required temperatures the engine oil for running in has a different specification than the one for normal use after the first oil change.”
So what’s the secret in this running-in oil?
“Usually it’s a very basic, mineral oil based engine oil. It doesn’t have any special additives but simply different levels of additives. For example lower levels of viscosity improvers to create the optimum coefficient of friction between moving surfaces for plastic deformation to occur at high temperatures. On the other hand it needs a higher level of other additives, called dispersants, which keep abrasive particles suspended within the oil to transport them to the oil filter or sump plug magnet.” So – gently Bentley with the revs and load, maybe using a more basic engine oil or one designed for running in, steady away till the first service – that’s all very well for road bikes. But what about a race bike?
It’s a very different scenario of course – competition motors are built by experienced engine builders, for a short, violent life. Here, they don’t give a feck about a bit more mechanical noise, or heavy oil consumption after 80,000 kilometres – the motor will be torn apart again for a full refresh long before then. Rather, we want lots of power, made in a reliable way.
Les Pearson of the PATA Yamaha WSB team is a genuine legend when it comes to BSB and WSB engine building. He told us how he runs in a motor. “Running in, it doesn’t really need much if built right, basically just to bed everything in, let the valves settle in the retainers before being over revved. You can use mineral oil first, some people recommend that, but I’m on the fence there.
“For me with a brand new motor, half an hour on the dyno or track, avoiding high rpm or max load, let it cool then you’re good to go. Re-built engines are similar to be fair.” Will the world end if you don’t run an engine in though? Les reckons probably not. “Over the years I’ve had some engines go straight into race mode, no run-in and the result hasn’t been any different. But better safe than sorry.”
Simon Green is crew chief for the Bournemouth Kawasaki BSB team, and also runs his own workshop, Track-Pro. He’s been working on race bikes for decades, and has a break-in routine he uses on all his race engines. “From brand new, I start the motor and gently warm it up to temperature in neutral on the stand. Then leave it to go cold. Repeat twice, then it goes onto the dyno. Initially I run it up to about 50 per cent max rpm, with no load on the dyno brake, for 10 or 15 minutes. At this stage I never use more than about 30 per cent throttle. Avoid constant throttle and rpm, and go up and down the gearbox as well as this also needs running in. Let it cool down again. Ain’t so difficult then.
“Now we start building up the rpm and throttle load in stages – ten minutes at 40 per cent and 8,000rpm, then ten minutes at 50 per cent and 9,000rpm etc. until you get to near 100 per cent and the rev limiter. Vary the throttle, rpm and gear constantly, just like riding on the road or track. To aid this I run a little brake on the dyno at this point, about five or ten per cent. It gives the engine something to work against and slows it down faster, again working bits of the motor not stressed on acceleration. Let it cool down.
“Finally, start it up, get the oil and water up to temperature and then let her have it! Two or three runs right up to the limiter, then a horsepower run. If it goes and throws a rod at this stage, reduce your engine builder’s privileges…
“Even after all this, I like to see a couple of steady ‘installation’ laps at the track, then in to the pits for a visual check-over. Although a dyno sounds dramatic at close quarters, it’s nowhere near as hard on an engine as real track time, so it’s nice just to make sure.”
So there you have it – maybe the guys down the pub aren’t so far off after all.