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hello i own a cbr250r 2014 model but now there's a burning smell like coming from the engine... is it possible that my piston and rings are damage?? whats the symptoms of a damage piston?? my bike is running smooth though.... and it felt like my bike is always overheating,i can feel hot air in my legs while riding.. but the heat indicator never cross the 3 point... thank you... and sorry my English is not good but i hope you understand...
 

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Have you noticed any drop in power since the "burning smell" started? Have you noticed any reduction in fluid levels (oil or coolant) since it started? Have you changed the oil and filter lately?
Check the engine for small oil leaks, especially the oil filter cover bolts. Even a tiny oil leak can migrate down the engine to the hot exhaust and cause a burning smell. If you do actually have piston damage, you should be noticing more symptoms than just a smell, like exhaust smoke, engine "knocking" and/or a noticeable decrease in engine power.
 

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As TF noted - it could be just a small drip of fluid on a hot part.

Make sure to keep track of the oil level on the CBR. It doesn't hold much, and it's the first thing that will kill the engine if not kept track of. Use good oil, preferably full synthetic.

Check the coolant level as well. Coolant has a sweet smell that differs from oil.
 

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Honda: INNOVA125i(2010); CBR250R(2013)
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now there's a burning smell like coming from the engine... is it possible that my piston and rings are damage?? whats the symptoms of a damage piston?? my bike is running smooth though
If you don't feel a performance drop type problem, and there are no suspicious noises, I would bet that the burnt smell is the result of some dirt sticking to the engine and burning on it, for example: Nylon bag. When that material finishes burning, the smell will usually disappear as well.
Try to check it:
  • With a strong flashlight
  • When the motorcycle is standing safe,
  • Engine is running,
  • Be careful of severe burns, especially from the exhaust which boils at hundreds of degrees.
 
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Honda: INNOVA125i(2010); CBR250R(2013)
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it felt like my bike is always overheating,i can feel hot air in my legs while riding.. but the heat indicator never cross the 3 point
The three lines tell only part of the story, if you ride at high RPM, at low speed (let's say in traffic jams), and in 40 degree heat, then it's clear that the engine heats up beyond average even though you only see 3 lines on the scale.
If the engine gets very hot, there a chances that you also lose a small amount of coolant, because the pressure rises, and the fluid becomes thinner (less viscous), then it escapes from the pump's mechanical seal, and leaks through the drain hole at the bottom of the right engine case, see the video I edited below.
So It is important to follow the coolant level and fill with the liquid recommended by the manufacturer.
 
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I'm with JKV. If you smell it after you shut off the engine, it's most likely oil or coolant dripping on your hot exhaust. Try taking your exhaust heat shield off along with the lower fairing and see if you see any signs of dripping on the exhaust. Run the engine up to temperature. You should see the issue. If you are burning oil in the engine, you are going to need an engine rebuild with rings and a re-hone of the cylinders minimum.

As a side-note, if your engine feels like it's over heating, it's probably spraying coolant on the exhaust. If you haven't damaged your engine, a $30 water pump repair kit with bearing should fix it.
 
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