Talk:Motorcycle Break-In Procedure

From CycleChaos
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Break in procedure used to be very important years ago (like 30+) but todays motorcycles really do not require any special sort of treatment at first. The various manufacturing tolerances were comparatively sloppy in your Dad's old Triumph, the possibility of having an engine assembled with a too large part installed in too small a hole was a very distinct possibility, so the prevailing wisdom was go go at it super easy at first-ride slow for the first 1000+ miles.

Back when I was wrenching on Honda motorcycles in the late 70's (Yeah, I am an old guy)we simply echoed Honda's recommendation for break in, that was simply "Don't over do it". After having worked for years on bikes since then I think that pretty well sums it up. So what's changed? The parts produced today are manufactured to an extremely high tolerance. Call it quality - this way every engine is as close to perfect as possible.

During break in what are you breaking in, really? Different parts of the engine have different requirements. The piston rings need to be run hard for the first few minutes, but other parts won't respond too well to this. Indeed after I finished a rebuild on a customers bike the "break in" was to run the bike up and down the street as hard as I could within reason, one wide open blast would seat the rings properly. Piston skirts fit in the bore with a fairly tight clearances, but other than guiding the piston don't get any real load applied to them. Late model engines use slipper pistons with a very abbreviated skirt. Although these parts don't really need an extended break in period it's best to avoid high heat situations for a few hundred miles.

Other items, such as the cam shaft, cam followers and tappets should not be exposed to high speeds for the first 100 or so miles, these parts are rough from the factory and when they first run will generate a fair amount of friction (and heat) until the faces of the tappets and lobes of the cam get polished off. Will running the engine at high RPM damage the cam before 100 miles? Not if it's only for a short burst(less than 30 seconds)but extended operation at red line on a brand new cam can't be good for it. The heat could get excessive and possibly damage the hard facing on the parts. I have occasionally seen the hard facing on a cam or cam follower fail after a great deal of mileage had accumulated on the bike, I would suspect this was from a lack of lubrication in the past or defective parts.

The crank shaft big ends are finished to a mirror finish at the factory, as are the bearings and require almost no break in time. Note that very little wear takes place here over the life of the engine providing it's well maintained. The largest enemy of rod bearings and crank journals are a lack of lubrication, dirty oil can clog up oil galleries causing a lack of lubrication, also grit and grunge can abrade these highly polished and tight fitting surfaces accelerating wear. Once a rod bearings is damaged complete failure occurs very quickly. If you hear a low tone knocking in your engine at idle along with low oil pressure it's time for an overhaul - sooner rather than later.

The transmission runs at a slower speed then other parts of the engine and generally have less precise clearances, not that I am saying it's sloppy, but compared to big end bearings it's pretty loose. The shift drum and shift forks comparatively move very little, it can take several thousand miles for the shift drum and shift forks to smooth out and provide you with silky smooth shift action. The gears themselves will not overheat if run hard at first, but it's best to try and keep light loading in the transmission for the first 500 miles or so. Lay shaft and counter shaft allow the gear clusters to move back and forth, once again small movements here, break in may take a few thousand miles before optimum shift action occurs. The transmission shaft bearings generally are caged ball, good to go in just a short time.

So, what's the real deal? Some motorcycle manufacturers, like Kawasaki and Triumph and Harley-Davidson will give you RPM limits, although a good guide can actually do more harm than good by inviting lugging and excessively slow speeds with reduced cooling, so the first thing to understand is don't lug the motorcycle. More damage can be done by doing that than by riding too fast at first, faster is better than lugging. You don't want to build up a great deal of heat, so moderate speeds and avoiding traffic for the first few hundred miles are always a good way to go. Some like Honda and BMW just suggest that you ride normally at first with no full throttle operation.