03 YZ450F Engine lockup! not cool!

6 replies to this topic
  • martis_d

Posted December 12, 2010 - 09:14 PM


2003 yz450f has had a new cp piston and rings(13:1), cam chain and pasted the valves for a fresh seal. put it back together and ran it for about an hour then i took it in the beach races, it went the best it has ever done never had it pull that hard. i stripped it down and touched up the frame, greased n cleaned everything. the bike sat for 12 or more months then i pull it out of the shed and took it on a forest trail for the arvo. the bike went good till the end after it got warm it was a hard to start and kept stalling worse then ever before. then at the end of the trail the bike started not idling and breaking down having *** moments. i check the carb nothing abnormal and the plug new. no change. then i took it out to another trail with a mate and after about 10 mins putting around and not idling i decided to give it a fang the in third gear it lock the back wheel and came to a stop. i took it home and tore it down to find the piston intake and exhaust side have marks in them and the wrist pin has mark on it. is there anything i should check for inside? the valves are all good nothing touched but the bike was binding up tight on the kick started? plz help!

  • Aka.Goose

Posted December 13, 2010 - 10:08 AM


Yet another thread that sounds like the rod bearing is seizing...

  • grayracer513

Posted December 13, 2010 - 11:18 AM


That would be my guess on an '03. Not an unheard of problem with that year.

Storing a bike for a year is an invitation to rust and corrosive damage to all of the bearings in general, particularly if the oil was not changed first.

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  • martis_d

Posted December 13, 2010 - 04:45 PM


will have a good look and i will also check out the oil pump as i think it may have lost oil pressure

  • zukboy789

Posted December 13, 2010 - 04:52 PM


The siezed rod bearings is probably whats wrong. Also, the oil pump wouldnt cause the marks on the piston in any way, shape or form. Another reason i love 2 strokes! :thumbsup:

  • grayracer513

Posted December 13, 2010 - 06:58 PM


Also, the oil pump wouldnt cause the marks on the piston in any way, shape or form.

Why wouldn't it?

  • martis_d

Posted December 16, 2010 - 04:56 AM


i have found the lower con rod bearing notchy will be a full on split the cases. whats the best way to go now new crank assembly hot rod or a big bore kit or stick with the stock and run a high compression piston like i was(13:1)???????????????????

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