hi all not been on here for a whle. i have a yamaha dt125r 1999 i started the bike a few weeks back and there was a rattling sound from the engine. turned out top piece of the piston had broke of and most of a ring. some of the cylinder had got a little scraped i used a wet and dry sand paper to smooth the marks out. ive put in a new piston and rings the same size as the original its never had a rebore. i road the bike and it was ok for a few miles but then stopped on me and now will only start when its sat for a day. when im riding its ok slow but when i bring the revs up to go faster its stops. when it starts it will iddle fine and sit running over no problem. theres seems to be good compression even though i havnt done a compression test. when i first replaced the piston and rings i got new 2stroke oil i put it in but like a plonker didnt read that it was for self mix and not injector like my bike is. i also put a little 2stroke oil in the tank as the guy in the shop said it would be good as i had a new piston and rings. ive since got all that oil out and put in a suitable 2stroke oil. but still its not running right. i gave the power valve a complete clean and when the ignition is switched on it moves free and does its clean. im thinking of checking the power valve again and maybe gving my carb a clean. but ive got a bad feeling ill be needing a new cylinder. hope some one can shed some lght on what might be the problem ?. rus
-- Edited by DTRUS on Monday 16th of January 2012 05:57:16 PM
hello bud i bought i new engine recently that had that same problem reli slow low on power i could ride it for a few miles but then it would cut out and not start for at least a day it turned out piston was chipped ring had gone scored the barrel to **** ! so i striped it down new piston rings and a rebore was recommeded for me hope this helps cheers
yer the cylinder head i have is in the same way as yours. i spoke to a guy thats repairs bikes and he said to me aslong as the cylinder is not too bad it should run fine. i wasnt sure if it was a problem with the power valve not set right so i tryed it with it pegged and it was still the same. im wondering if the carb could be blocked with the wrong 2stoke oil i put in. :S. cheers for the pics james. good luck with the rebuild. ;)
yeahh see if it was in same shape i wouldnt recommed just chucking in new piston and rings for best results i think a rebore is best , mate i was there for days thinking it was my carb i got so frustrated i allmost sold my bike lol so was glad to find that it was a top end rebuild cuz i new the problem lol
i ment my cylinder head was dinked like yours i cant see what condition your cylinder is in from them pictures. theres not much i can do about the dinks in the cylinder head i have and it shouldnt make much diffrence i believe. wont take long to give the carb a once over and then atleast im narrowing it dow. off to the shed with me. lol cheers
Sounds like it needed a rebore m8, did you retive part of the piston as some of it could have got in the bottum end, id say buy what i hear you need to do it all over again with a rebore. what coars wet and dry u use?
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best way is to strip the engine any thing could of got wedged in the bottom end, if theres a piston break up you should really strip the bottom end and flush/clean out all the pieces eb=ven the smallest bit can wreck a toip end
if i had a quid for every engine iv had brought me where tev just chukked a top end on it with out going fishing in the cases for debris id be well off ha ha
