A forum for owners of Yamaha TTR250 trail and enduro bikes!

zoid · Member

Aftermath of water/rocks

TTRfan · Super Guru

Looks like a Yamaha piston. Is it a standard one or oversize? If oversize it will have 50 or 100 stamped on the crown.

If it is the standard size then the groove could be up to .50mm deep and be removed by reboring and using a standard oversize Yamaha piston. Much deeper and you may have to consider a +1.50mm or +2.00mm after-market piston.

If you are not sure then take the barrell to whoever you are going to use for the rebore and ask them to check which piston you will need to buy.

Brian

zoid · Member

Say I take it to 2.00mm will i need to chance anything else?

TTRfan · Super Guru

Unless you make other changes then the carb settings will be OK. Don't forget to clean the head and valves up whilst the head is off and fit new valve stem oil seals whilst you have the chance.