well i heard from some people that ur suppose to rebuild ur engine every 10 000 km and my mxz 670 is starting to get there. to get it rebuilt will probably cost around 1000-1500 dollars. so i was wondering how hard it is to rebuild ur own engine? i did it once in auto class with a 4 stroke but i know 2 strokes are quite differnt. i would be also boring it out 2 over to make it a 685 so i can get wiseco pistons and rings and the clips and everything for 300 dollars. then to take it in to machine it 2 over will cost probably another 50 dollars. but how hard is it to rebuild ur engine and are u actaully suppose to do it every 10 000 k? i would most likely take the engine out and bring it into my room over the summer to do it so i can have some time to do it right. to be able to order my pistons from royal they want you to know a lot of stuff. i will write it out after someone tells me how hard it is to rebuild it and if i would be able to figure it out. if i do end up doing i will be asking many many questions on here. thanks for any input.