why is there a run-in period for new cars and motorbikes?

Question

I hear a lot of confirmations that running-in is a good idea but no solid science/engineering/evidence as to why. Please don't tell me how to do it, the question is why.

Answer 1

The break-in (run-in) period is to give the engine mainly a chance to let all the gaskets and seals set properly. If you don't follow the brek-in instructions, it will be very hard on your engine and will cause problems down the line. Remember also that if you ever change gaskets, o-rings, seals, or internal engine parts (pistons,rings, rods, camshaft, cranks, etc.) that you re-do the break-in period.

Answer 2

When you make parts, there is a certain point where the cost of making that part very precise makes the part not worth in to produce. The run in period is set so that the piston and the cylinder can wear away the differences so that they match up more perfectly. That is why they tell you not to run the engine hard during that period. Instead of gently wearing away a piece that isn't needed, you hit it really hard breaking the unwanted piece off and a little extra which can crack the piston or even the cylinder. That is also why if you have a piston replaced the mechanic tells you to take it easy for the same period.

Answer 3

Take it easy over first 500 miles or so, dont rev hard though better to let it rev a bit in a low gear than to labour in a high gear, the latter is the worst thing for a new engine. Then slowly let it stretch it's legs for another 1000 miles or so after which all should be fine.

Re oil change, two schools of thought: 1/Change after 500 to 1000 miles to remove initial running in deposits. 2/ Leave original oil in for at least 5000 miles or so to help bedding in. I guess take Ford dealers advice, where as Ford are worried about fleet service costs so will not recomend an oilchange until I guess 12.5k, the dealer will happily charge you for an extra change though should not do so if they think it is completely unnecessary, i.e. they should be fairly objective.

Otherwise oil change every 6 months whatever the mileage.

Some manufacturers specify oil changes at 20,000-mile or two-year intervals or leave it to the car's service indicator computer, and give no indication of when things like timing belts should be changed. What is your advice?

After the first year or 10,000 miles, whichever comes first, I recommend using either a good semi-synthetic oil such as Texaco Havoline 5w/30 (Ford dealer 'bulk' oil), or a fully-synthetic such as Mobil 1, and changing it every 5,000 miles or every six months, whichever comes first. If you are a higher-mileage driver doing 15,000 miles a year or more, consider stretching your oil changes to 6,000 miles. If you do 25,000 miles or more and use fully-synthetic oil, consider stretching to 7,500 miles but no further. Always change the filter as well. Change the manual gearbox oil once after the first 12 to 18 months, or 10,000 to 15,000 miles. Change the coolant every 3 years if it is an MEG coolant, or every 4 years if it is an MPG coolant. Change the brake fluid every 2 years unless it is Dot 5 silicon brake fluid (unlikely on a mass-produced car). If the engine has a timing belt, change that every 3 to 4 years or every 40,000 miles, whichever comes first, unless the engine has no history of premature timing belt failures (Ford Zetec E and Zetec S engine timing belts generally exceed their design life of 80,000 miles, so can be changed at 6 years or 80,000 miles, whichever comes first.) Change the timing belt tensioner and any weeping camshaft or jackshaft oil seals at 80,000 miles (every second timing belt change for non-Ford Zetecs). VAG belts generally good for 60,000 miles. Early VAG 1.8 20v engines had water pumps with plastic impeller which can fail, throwing off the belt, so belt and water pump should be changed by 60,000 miles.
If the engine comes factory-filled with special, very expensive recommended oil, be aware that if the engine is not run-in properly it could use oil at the rate of 1 litre per 650 miles, so it changes its own oil four to five times in 20,000 miles at a cost to the owner of around £275. It seems that to allow for these long oil change intervals manufacturers raised the level of contamination and degradation acceptable in the oil.

What's the best way to run-in a petrol engine?

Put the car on a rental fleet so it is driven by a lot of different drivers with different driving styles. Seriously, modern petrol engines are built extremely 'tight' so they need a bit of wear during the first 10,000 miles for the piston rings to bed properly into the bores. Leave factory fill of oil for the first year or 10,000 miles. An early oil change to fully synthetic can prevent this happening, as can driving at low engine revs and driving at steady speeds. So, depending on the engine, self-impose yourself yourself a rev limit of between 4,000 and 5,000 for the first 1,000 miles, and be sure you vary your revs and occasionally reach that limit. After 1,000 miles, common sense dictates that you won't rev the nuts off the thing straight away, but you needn't be too worried about hitting 6,000 rpm occasionally as long as you vary the engine speed. Try never to rev to the rev limiter as the misfire this causes can damage the catalytic converter matrix. Don't change the oil and filter until the first manufacturer recommended change point, or the end of the first year. After that, if you intend keeping the car for a long time I still recommend more frequent oil and filter changes than the manufacturers or their on-board service indicators suggest. It's also a good idea to have the transmission oil changed after the first year to get rid of any swarf which could later be ground up into tiny particles which eventually get into the bearings and accelerate wear.

Answer 4

run in periods as you call them or break in as they may be. are used for actual break in and sealing of the piston rings. there will be a nominal amount of wear occured during this period. automotive manufactures recommend varies things and oil changes due to this factor to keep there warrenty valid. I myself always express to my customers to break there vehicle in like they plan on driving it... if your going to drive it at 55 mph then break it in that way. if your going to drive it 155 then break it in that way.... regardless how you drive it be it slow or fast if it has a problem it will let you know fast or slow. what the manufacture suggest is for oil change times to avoid unneccesary brake in metal in the oil system.

Answer 5

This is informative.

http://www.enginesonly.com/break-in.html