over-revved

[Akiraprise]

hi all, not that mechanically literate, but oh well .

Basically I was at a traffic light yesterday and some chav twat came up to my bike and pinned the throttle back, it was held fior about 3 seconds wide open before i punched him in the face and took the keys out.

anyway is this gonna damage my bike? For some strange reason it seemed to charge my flat battery...

[Git]

It shouldn't of done much harm at all, not the best thing to do to an engine with no load though. If it sounds fine and feels fine then I bet the motor is fine.

[simon1221]

Rev it right into the red?

I guess it would charge your battery, as the gerator will be generating a lot more power at higher revs
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DNA50 (sorry) ->> TZR125l >> GPZ500S

[Akiraprise]

but my battery DOESNT charge at all on normal riding, and seeing as it's a 50cc it's allways being redlined (10-11k). But after that blast of power my horn worked a little bit, it's gone again now though

[mchaggis]

Revving a warm/ hot engine under no load will do virtually no(read none) damage to it. The engine was positioned normally so the oil would be in the right places, and being warm it would be flowing round fine.

Damage to engines under high revs happens when they are held at high revs for extended periods causing overheating, or when they are lying in funny positions (dropped/ binned/ crashed) meaning that the oil doesn't go where it is supposed to so parts sieze from lack of lubrication.


Edit: If it's a 50cc two stroke, then the oil flowing is irrelevant, and it would be difficult to damage it at all unless it wasn't getting any 2 smoke oil (blocked pump/ no oil etc). High revs and overheating would be an issue over long periods, but not for a few seconds.
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I must not be a troll...
Mmmm, Guinness
Discovering the delights of Hammerite and a 3/4" brush.

[BlueNinja]

2 strokes will not rev to the redline if cold, even if you pin the throtle back.

No worries, 3 seconds is nowhere near enough to cause damage.

Oh, and well done on biffing that chav I would have got off my bike and made things messy if he did that to my zxr
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Big Kawasaki ZXR 400 project here:
https://www.theundertaking.com/index.php?showtopic=483

[DM]

This is a relief to hear as I'd always figured very high revs in neutral for any period would cause wear. I was fooling with my carb once and raised the needle a notch to try and solve a flatspot problem. When the bike finally started it shot up to 12-grand (red's at 9 1/2) and really worried me, as I was sure it was going to heat up very quickly and seize . But would being an air-cooled engine make it more likely for this to happen?

[simon1221]

Yes,

Especially if you are standing at a junction, as there will be no air going over it.
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DNA50 (sorry) ->> TZR125l >> GPZ500S

[BFG]

3 seconds on a warm engine will be fine.

I would never rev an engine hard under no load. An engine is a power source. Energy from the exploding fuel is designed to be converted into kinetic energy at the crankshaft, which is then used to propel you forwards.

Given the first law of thermodynamics - "energy can neither be created nor destroyed" - when it doesn't go through the gearbox to the back wheel, where does it go?

Actually it gives the engine internals a bloody hard time, which is why engines vibrate a lot more when they're revved like that. People do it all the time and often don't experience any visible negative effects. Doesn't mean the next owner will be trouble free

[instigator]