Yeyet wrote:
JKJ-FZ6 wrote:
...and they get a new engine or a complete rebuild between races.
What's could be the reason for this? The way the engine was broken-in or the result of the race itself?
As an ex-race technician I can tell you it's the way the motor is designed and the way the engine is broken in.
Firstly, a race engine is built with very sloppy tolerances, especially the cylinder bores, pistons and rings. If you ever listen to a big race engine it's very noisy mechanically. It sounds like a bag of nails in a tin can. Ring gaps are large to allow for expansion. Pistons and rings rattle, especially when cold. However, the big clearances/tolerances are there because during the race the engines and the internal components get super heated at race speeds. Because the pistons are super lightweight they expand considerably to fit snug in the bores. They can take the heat and this is where the engine produces it's most power. But the hard break in they get detracts from overall long term life of the engine. The engines only have to last a few races between strip downs so that's ok.
A road bike must last as long as possible. It is built with tight tolerances. To protect the engine, owners should follow a more gently break in as laid down in the owners manual. But you should not drive it slowly or it won't run in properly. However, use of too much power with too wide a throttle setting and too higher revs can be detrimental to a road engine in it's early days. Individual components in the engine such as pistons, bearings and cylinder barrel surfaces are still quite rough and soft when new and need to work harden and smooth themselves down during the first 1000miles. This smoothing in for a snug fit is not just a mechanical thing. It's also a CHEMICAL thing. The surfaces of the cylinder bore for example has to work harden through these chemical changes, as do other engine components. If you hurry the process the mechanical changes happen, usually by taking too much metal off the bores, but the chemical action/changes don't happen properly. This means you get a cylinder bore that will wear out more quickly, as will the piston rings. To avoid being damaged and to give the engine long trouble free life and good power output withoiut using oil, this should be done following the manufacturers advice, not a hard break in. I've seen plenty of hard evidence that hard break ins do long term harm to engine reliability, power output and economy. Plenty of people claim to have done it and say their bikes are fine, but they often only keep them for a year or two or three, covering only a few thousand miles, so never ever get to see the damage they have done.