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Discussion Starter #1
Have a 100 hr te 300 husky that needs new rings and so thinking of changing the pistion whilst I am there

how do I make sure I get the right piston size ?

one guys was saying take the exhaust off and there is a number stamped on the engine either 001 or 002 to let you know ?
 

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Same as what came out. Clean the piston top and it's size is on it. At 100 hours get the same, Nikasil is harder than the rings, the rings are harder than the piston. Piston itself wears first, then rings and eventually Nikasil. What does your piston look like? If the faint horizontal lines are still present on the piston front and rear, I'd put it back in. I change mine when the front (exhaust side) is polished smooth and shiny. You might be able to just slap new rings and a small end in for piece of mind and run it a good while longer.

I only went to a B piston on my 150 at 100+ hours as it's revving its tits off. A 300 is never working hard unless you supermoto them!
 

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I have always put in next size up on my 300 (generally at about 120 ish hrs)
 

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Just measure the bore. Any half decent CNC / engineering shop will be able to do this for you in 5mins with a bore mic.

If you're guessing i'd stick a B in there. Mine needed a B in my '17 300 at around 100hrs which was correct size after measuring bore.
 

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Clean the top of the piston. The number of the diameter are marked into the crown. Can't go wrong then.
 

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Discussion Starter #10
Mate that is the best idea ...worked like a treat - shame I didnt read that line the first time you wrote it !

https://photos.app.goo.gl/A7LX4QNFf23CCRpz6

so it is a number 1 then ?

big number 1 on it
71.925 written below it ?


so going to go and replace it with the same thing (not really racing much these days)

and I read on here that vertex are decent pistions so .. on ebay these things are £120 and cheaper than the OEM ones

This should do it .. right ?

"Vertex Piston Kit KTM EXC 300 Single Ring Inc Pin & Clips 2004-14 Size A 71.94mm"
 

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Mate that is the best idea ...worked like a treat - shame I didnt read that line the first time you wrote it !

https://photos.app.goo.gl/A7LX4QNFf23CCRpz6

so it is a number 1 then ?

big number 1 on it
71.925 written below it ?


so going to go and replace it with the same thing (not really racing much these days)

and I read on here that vertex are decent pistions so .. on ebay these things are £120 and cheaper than the OEM ones

This should do it .. right ?

"Vertex Piston Kit KTM EXC 300 Single Ring Inc Pin & Clips 2004-14 Size A 71.94mm"
Yep, Vertex are good and i believe produce the OEM pistons for KTM & husky, Beta, GasGas 2strokes anyway. Just be warned the circlips are a real fucker to fit! Keep your old one to practice is my advice.
 

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Why would you fit a single ring piston?

I’d be more inclined to fit a a twin ring piston like the oem one.
 
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