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I own a Honda Stunner 125 CC motorcycle. I bought it in 2009. Since last year I have observed that it is emitting white smoke.

Mechanic recommends that I purchase new pistons or after some time engine would seize and then I would be paying for entire engine and not just pistons.

Questions:

  1. What is making smoke white in color? Is this really ripped piston or something else?
  2. When I am out to purchase new set of pistons how to verify this piston is good this is not? I mean brass coated, copper coated, rings, two rings etc .
  3. Would it decrease the consumption of engine oil and petrol (gas)?
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    You should be able to replace the piston rings without replacing the entire piston. It'll be the same amount of work either way so if the piston isn't too expensive you may want to go ahead and replace it anyway, but unless there's excessive carbon build-up or something's obviously wrong with the piston I'd just replace the rings. – TMN Jun 24 '16 at 18:28
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If the smoke being emitted from the exhaust is white with a hint of blue, it is oil. If the smoke is white with a sweet smell, it is antifreeze.

As Anarach pointed out in the comments below, yours is an air cooled engine so there is no antifreeze.

If you're burning oil, it definitely could be leaking past the piston rings, which would likely be fixed if you replaced them, though the problem could also be with the cylinder walls, so you should inspect that they are smooth before reassembling the engine. I quick search indicates the engine in the 2008 Honda Stunner 125 is the Honda JC40E, so that is indeed your bike, make sure the pistons you buy are for that engine. I would stick with whatever material and number of rings that the OEM (Original Equipment Manufacturer) pistons and piston rings were made of.

If the piston rings are in fact the problem, replacing them will likely reduce or eliminate your oil consumption, and increase your fuel economy.

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    Its an air cooled engine of a motorcycle, Does not use Antifreeze. Its probably the piston rings. – Shobin P Jun 23 '16 at 11:32
  • @Anarach I did not know that, thank you! – MooseLucifer Jun 23 '16 at 13:02
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1) I'd guess that the smoke is oil that is burning. If the piston/ring is bad, it could be allowing oil to be burned with the fuel.

2) Just make sure you buy a good quality part that fits your exact engine.

3) If the piston/ring is your problem, then oil consumption should decrease once fixed.

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