NSR125 piston damage

[Tony Norton]

Hello all,

has anybody experienced anything like this (see attachment).

If so, do you know what caused it? The erosion is about 2mm deep.

Cheers

Tony N

[alains]

hi tony ! back in the uk ?
i think you had a seizure due to overheating . probably a too lean mixture or too much carbon in the engine . sometimes also a burn plug can do this damage . i think the barrel is worn too , look the coating between the 2 exhaust windows
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the worst day fishing is better than the best day working

[Tony Norton]

Bonjour encore Alain,

Ca va bien j'espere?

I think you were right about the plug (see attachment).

I can imagine it continually glowing red-hot and burning everything in range. You can see that not only is the earth electrode burnt away. it is also bent to to one side. Visions of lumps of hot aluminium flying around in the pot.

Mon petit fils. Il est tres mechant. Pas du travail, seulement montes et allez. Eh bien, encore du travail pour le grandpere!

Au revoir et bon chance mon ami.

Tony

[satelliteone]

Hi ya chap, From experience, i would have an educated guess and say it has been running very lean. Check your carb, and thats its jetted correctly and also for any air leaks getting in other than the route through the carb itself.

You can see in your pictures the lack of fuel to air mix has caused uneven burning, and burning in one area. The result of excess heat has eaten your alloy. Complete rebore and new top end im afraid.

When you`ve rebuilt it, do the plug chop method and see if your plug is a nice meduim brown colour. If not you might have to upjet.

good luck, hope you get it sorted
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