Iv got a 01 yz250.it dosent click into 5th gear.All it does is make a clunky noise like its trying to click in but nothing happens.1n234 are algood.anyone know whats happening??

5th gear out is a pretty general description, Is it grinding when trying to shift into 5th or when you go to 5th it pops out, or you shift into 5th and nothing happens? It could be a simple syncro repair to replacing just the 5th gear to rebuilding the whole transmission, either way, you may want to consider just buying a JY trans, it would probably be cheaper.

it sounded like an engine ping to me,, with low octane fuel you may be experianceing this,,try cleaning out all EGR ports and doing an upper intake/valve cleaning and checking any timing issues

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double posted , back up one.

check out the knock sensor it may be the problem

I have the same problem. on the passenger side under the fender you will have access to the transmission. Remove the cap on the end. You will need to drain the transmission fluid and replace all the gears in the end cap if damaged hopefully they are not and you can just tighten up the nut. What happens is a nut comes loose and backs off the pressure on the bearings and you loose 5th. I removed the entire transmission and opened it up. There is nothing wrong with the other gears, because your problem is with the 5th gear synchronizer assembly. I let mine go too long and I'm having to replace everything. Make sure you put the appropriate torque on the nut and hit it with a hammer to lock it down. This should really be designed with a different method of keeping that nut in place. It's costing me lots of time and now money at the stealership. Good LUCK.