Engine Break-In

[TexasCountry]

Does anyone know the real reason behind why motorcycle engines require break-in and car/truck engines don’t?


They’re both internal combustion engines.  Both have pistons, rings and cylinder walls made from virtually the same type of steel/aluminum, etc.

You can buy a new car or truck and immediately put it on the interstate at a constant speed for thousands of miles without any ill affect.

Why can’t we do that on a new motorcycle?  Could it be the higher rpm’s inherent on motorcycle engines that can cause the additional stresses?

Break-in is a pain in the a** and I don’t think anyone enjoys it.  Why can’t manufacturers make a motorcycle engine that doesn’t require any break-in period?

[Our Gee]

Who says Cars don't require a "Break In" (called Running In here in the UK). The much respected UK Automobile Association gives detailed advice on how to drive your new car during the first part of it's life. This advice mainly centres on Engine RPM, (with different levels for Petrol and Diesel engines). driving in too high a gear which would make the Engine to labour and gentle use of brakes. My own car, a 2 Litre Diesel had a very "tight" engine from new so it was important to follow the advice on not letting it "labour" in too high a gear. Now after 75,000 miles the engine is sweet as a nut, uses no oil and pulls like a train. Whether I can put this down to my careful "Running In" or not I don't really know. However I "enjoyed" following the advised "Running In" period.

[rnelson955]

I'm not 100% sure, but isn't pre-running in engines in the factory a thing? Maybe they do that on trucks where they know running it in according to limited guidelines isn't practical?

[Hors Piste]

Where do you get this odd idea that cars etc do not require running in?


This is from the manual for my Subaru:-


"The performance and long life of your vehicle are dependent on how you handle and care for your vehicle while it is new. Follow these instructions during the first 1,600 km (1,000 miles): . For petrol engine models, do not allow the engine speed to exceed 4,000 rpm except in an emergency. . For diesel engine models, do not allow the engine speed to exceed 3,500 rpm except in an emergency. . Do not drive at one constant engine or vehicle speed for a long time, either fast or slow. . Avoid starting suddenly and rapid acceleration, except in an emergency. . Avoid hard braking, except in an emergency."

[PatM]

There's a video from MCGARAGE floating around on the net of a comparison of two similar engines being broken in, one following the manufacturers recommended procedure, the other the ride it like you stole it way. They then disassembled both engines and found no notable difference between the two.
The guy, Ari, does give good reasons why you should break it in gently. No because of wear but for safety reasons.


[size=2px]https://youtu.be/xpoglovyy_8[/size]

[PeteM]

I suspect it may be in part because the average cage driver is clueless so if you told them to not go over xRPM they would not know what to do whereas the average biker has a bit more mechanical nous.

[Casbar]

There's a video from MCGARAGE floating around on the net of a comparison of two similar engines being broken in, one following the manufacturers recommended procedure, the other the ride it like you stole it way. They then disassembled both engines and found no notable difference between the two.
The guy, Ari, does give good reasons why you should break it in gently. No because of wear but for safety reasons.


https://youtu.be/xpoglovyy_8

There are also numerous theories on this, when racing we used to break engines in by a very different process, but basically thrash it. But and its a big but, you don't expect a race engine to last for 1000s of miles from the off, so even if two engines look the same, who knows which one would prove reliable in years.

[gogs01]

I've visited motorcycle factories and watched the pre-packing check where the bike is strapped to a dyno and run through all the gears - full throttle, to peak revs.
I'm therefore not too fussy about observing a conservative rev limit during my running in process, but I wouldn't want to abuse it with continuous high revs either, so I try to stick to minor roads where there will be more rev changes, gear changes, braking, cornering etc., in the belief that this will get everything nicely bedded in.
Hire cars are commonly hired out with minimal miles on the clock and I often wonder how they last after having been "run in" as fast as possible from one end of the motorway to another - as I'm sure some of them are.