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Four Fiddie

yz450 crank replacement--pictures

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HEy I am going to be tearing down my 2003 yz450 to install a new crankshaft(timing teeth are badly worn), ive been doing alot of research and it seems you guys and girls know your 4-strokes. Id like to give something back and post up digtal pictures of the complete job so it will make the next guys job easier. Im hoping you guys will give me your support for this is my first time tearing apart the bottomend. the status now is the engine is out of the bike, the cylinder head and cylinder are off the engine. Well this is what happened, I was riding at this local sandtrack and i was hitting this stepup that a 125 was clearing with no problem while my bike was struggling, the bike then was hard start, it took like 40 kicks, it started up fine though and so I did a few more laps and was beating the bike and all of a sudden it starts running like my xr100, no power, and sounds like an silenced king quad so i kill it and wait for my buddy to let him know im out of there, the 450 doesnt start, i was kicking the piss out of it, after about 200 kicks it starts(note that im a mile away from my truck on someone elses land so pushing it back wasnt an option) ,so i make it back and take it home, i com to find out--

---the timing has jumped off and so I adjust it, the chain was a little loose but i figure i could start it, so it starts perfect, i go to start it again and it wont turn over the timing has jumeped again, the camshafts are worn and the chain is stretched along with the cranshaft timing gear being spent and the front cam chain guide is eaten up, I ordered new cams, chain ,guide and crankshaft, should i get a new tensioner? it seems like the old one works just fine, also should i just replace the other timing chain guide? it doesnt seem to worn out. also has anyone bent a valve doing this?how would i check that?

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Man that sucks.

Tensioner failed and the extra super loose cam chain wore down the teeth from being so loose and jumping time a few times. This explains why it was so hard to start and why it ran like a xr100 becuase of incorrect timing.

To check to see if you bent a valve check where the all the valves seat against the head. If theres any gap between it and the head then the valve is bent. I have jumped timing once and I bent a valve, but mine jumped more teeth then yours, you couldnt even start mine becuase there would be valve to piston contact.

The part I would replace would be the front cam chain guide, the crank of course, both cams I would replace with hotcams becuase I believe the intake may be cheaper. I would replace the cam chain tensioner becuase this was why you jumped timing.

Where are you in connecticut? If you need help or get too pissed off at this thing I could help you out.

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hey thanks foir the input, yea ordering the tensioner is a good idea, it seems to be working thou but maybe it only takes one time to not work right and there goes my motor, I live in Bristol where are you from?

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berlin is close, you go riding in cromwell sandpits or portland? I work in middletown so i usually shoot over to one or the other after work. Maybe we could go riding one day let me know

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