Bore Diameter Check

[periclesgsilva]

Hello guys! After 148 hours on it, time to check my top end. Well, after disassemblying the dream machine, checked the bore and in one side, the mechanic say the size was 66.45. The biggest size in all cylinder. Near the "gas" entrance.
My question. To select a new piston (previously was Pro-X B), i need to use the biggest diameter of the cylinder or the smallest?
I have options, like the Pro-X E (66,38), but my question: there is a chance during the piston expansion to lock on the bore? Because the smallest size was 66,43.
Thanks! Btw, the old piston size was 66,35 (original size) but after measurements, 66,31.
I really don't know if the guy measure right. Today i will look for another option too with a 3-point check.

[periclesgsilva]

Updating the thread. New cilinder, new wossner piston. The only difference was the new cilinder come with B letter stamped.
3 kicks and the beauty start to make smoke.
Thank you guys!

[mtnmanseth]

She's refreshed and should be a handful... have fun!

[Ignas]

I havent seen anything that wear like yours in 150 hours (it might be like that if you like to rev it alot). But your cylinder was within specs, piston too.
All two strokes wear at exhaust port because of heat. if you are riding trails i think your jetting is off or you dont clean air filter. Maybe engine oil.
My 07 still with oem cylinder and it was used for racing at the track by the last owner.
My friend rides trails and changes pistons every 200-250 hours for his ktm. He puts next diameter every other piston.

[periclesgsilva]

Ignas after checking my cilinder I found the problem. Was slaved with iron piece instead of replate. Out of size

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[Zman]

You can always do a big bore kit!

[periclesgsilva]

After 40 minutes of slow riding with 2 stops to cooldown I give a hard way in the throttle. WoW. Perfect. Only my left radiator start to bleed. Maybe during the assembly some knock with the tool. Love the result

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[adriano.ro]

Originally Posted by Ignas

I havent seen anything that wear like yours in 150 hours (it might be like that if you like to rev it alot). But your cylinder was within specs, piston too.
All two strokes wear at exhaust port because of heat. if you are riding trails i think your jetting is off or you dont clean air filter. Maybe engine oil.
My 07 still with oem cylinder and it was used for racing at the track by the last owner.
My friend rides trails and changes pistons every 200-250 hours for his ktm. He puts next diameter every other piston.

Ok,so if my piston is B from factory( I have around 135 hours with OEM piston) the next one must to be one size bigger so is the C and after de C I need to replate the cylinder? ?

[Ignas]

Originally Posted by adriano.ro

Ok,so if my piston is B from factory( I have around 135 hours with OEM piston) the next one must to be one size bigger so is the C and after de C I need to replate the cylinder? ?

You have to measure cylinder for wear and pick the right piston. If you dont want to measure and you are sure that its 135 hours just put the same size piston. Better buy forged piston but remember that you need more piston to cylinder clearance than cast.
Also check your rings end gap before installing the piston.

I see that you are from Romania, where do you ride? We have been in Sibiu couple times and plan to go there next year. If you live nearby maybe we can meet and you could show us some trails.

[adriano.ro]

I'm from North of Romania,600 km from Sibiu you enter in Romania on the north side,we can span some time around here. I live near Hungary border.

I use always Wossner pistons,forged pistons. After this hours the bike start really easy cold or hot,and I still have good compression.