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PISTON PROBLEM, HELP!

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i own an 04 Aprilia mx 125 2 stroke supermoto. the bike has been great, however, yesterday i went out for a little ride, and i warmed the bike up for 10 mins, 2 stroke tank was topped up aswell as the petrol tank, and it fired up first kick, for the first 15mins of the ride i took it easy to help warm it up quicker. then after that it was great for about 10mins, the power valve was kicking in as it should, but after that i started hearing a rather odd tapping sound coming from the engine, and as i carried on riding, it just got louder, the only time you couldnt hear it is when the power valve kicked in or when i held the clutch in and let go of the throttle. after this, roughly 30mins into the ride, i noticed the bikes power had decreased, i mean this bike is quick, but last night it just sounded hell loud, it was still moving, but not as fast as it should and normally does. so then, i turned onto a straight road near my house, and throttled the bike from 2nd to 4th and it wasnt pulling, aswell as this, the gear shifts felt sluggish at high rpm, so i slowed down to turn back around, and i double clutch down shifted from 4th to 3rd, and the bike bogged slightly, so i then held the clutch in to rev it up abit to keep it stable, but then it bogged badly and just died. so i waited for about 2 mins, just inspecting the bike, then i tried to kick it over but it wouldnt start, it had compression so i wouldnt have thought it was the piston. so i tried to bump start the bike and i managed to get it started, however, it sounded terrible, i literally had to rev it up high as it just wanted to die out, it wasnt even bogging, instead it just sounded like someone kept turning the key, so i let it turn off, kept it on the stand, and tried to kick start it, but the kick start was just stuck at its highest point, it wasnt kicking down at all as if it was jammed there. this morning, i contacted a mate to ask him what the problem could be, he said that it may be heat seized and that i should take the spark plug off and pour some 2 stroke down the hole and then try kicking it over, but no luck. so i took the head off and saw that the top of the piston had loads of scratches on it, as well as very small in dents round the sides. however, i cant see any scratches on the barrel, but i think its best if i just replace the barrel and piston. thing is, ive never done a top end before, been watching vids, it doesnt seem to hard, and the barrel and piston are a kit, so they come together, so will i still need to get them measured or whatever needs doing, and can you explain the steps of replacing the top end

thanks 

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Edited by samrs6

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Since there aren't too many 125 2-stroke modern street bikes you are really better off hanging out with the dirt bike folk in the Supermoto forum and general dirt bike discussion.
http://www.thumpertalk.com/forum/27-supermoto-supermotard/

At a guess the weird noise you heard might have been detonation, but something like a bearing could have let go too. The older experienced folk and mechanics that hang around the general dirt bike discussion should be able to help diagnose your problem. You might need that so that you know what to do next. 

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@stinkwheels, just took apart the cylinder head and took the piston off, seems like the bearing for the connecting rod is the problem, because the connecting rod keeps getting stuck which is why the kickstart wont go down

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