bike seized...kinda

07 yz450f.

 

today I was riding and all of a sudden the bike made screeching noise and locked up, once i was off the track I tried to turn it over but the kickstart was frozen. I was convinced It was blown up. when I got home I washed it and tore down the top end. I was stumped, I found nothing wrong. the timing was good, chain was tight, no bent valves, piston, rings and cylinder looked great. Then I started turning the bike over to see If I could find anything wrong with the bottom end. nothing! so I put the bike in gear and spun the wheel by hand to see if any of the gears were messed up and once again nothing.

 

what the hell happened? what should I do?

Check the rod bearing clearance, "F" in the picture here.  I know it says, "small end free play", but the amount that the rod can be "rocked" left and right without letting the big end slide sideways on the crank is an indicator of clearance at the big end. 

 

If the rod bearing cage gets too loose, together with a little extra clearance at the big end, the rollers can skew out of line with the crank pin and temporarily lock the crank.

rod.png

Siezed cam bearing?

cam bearings are good as well as the whole valve train. Gray I think you are right, this is an original bottom end bike. What is the proper way to check these clearances? I am unfamiliar with bottom end work. what should I look for.

 

This sucks because I'm trying to sell it so I can buy a FI bike...crap

one more question.. If this is the issue can (should) I replace the rod, bearings and seals, or would you recommend replacing the whole crank and rod assembly? keep in mind I don't plan on keeping this bike much longer, but also I would never want to sell and innocent person a ticking time bomb.  

cam bearings are good as well as the whole valve train. Gray I think you are right, this is an original bottom end bike. What is the proper way to check these clearances? I am unfamiliar with bottom end work. what should I look for.

 

This sucks because I'm trying to sell it so I can buy a FI bike...crap

 

Look at the picture from the manual I posted.  You'll need a dial gauge. Your main concern is measurement 'F'.

 

 

one more question.. If this is the issue can (should) I replace the rod, bearings and seals, or would you recommend replacing the whole crank and rod assembly? keep in mind I don't plan on keeping this bike much longer, but also I would never want to sell and innocent person a ticking time bomb.  

 

Replacing the crank is quicker, and you can go with a Hot Rods crank to save a bit of money without giving up much on the quality side of things.  The problem with rebuilding is that by the time labor is added to do the press work and alignment, it may cost nearly as much as a new genuine crank.   There is a company called Mr. Crankshaft  that comes recommended by several people on the site, and may be able to help.

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