YZ250 bottom end help needed

Joined
Jan 18, 2003
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#1
I kinda went down in a mud pit and the bike fell over on me. I am working on pulling the bike apart now. I had a fun time getting the head off becuase the piston would not go down. I finally got the head to go up but since the piston would not go down I was not able to get the head off. I also tried to take the piston off but the stupid pin will not come out. There is so much dirt/sand in the bottom end so I took a whole bottle of WD40 and sprayed all over. I was finally about to push the piston down and get the head off. Now how do I get the Piston off without bending the connecting rod? (Yes I did take off the clips). I have never done the bottom end so any help/tips would be great. I rebuilt the top end on this bike and I have only put two hours on it. The only problem is I let the bike sit for 2 days before I was able to get to it. I have split cases before but this was on my street race bikes. Hopefully there is not much difference. I have the engine out and I am currrently rebuilding the carbs. The bottom end still turns freely except the piston does not move freely on the pin. I am hoping to completely remove the piston/pin & the crankshaft as one unit and soak it in something to make it loose enough for me to salvage the crankshaft. Does anyone know if I really have to have the special tools to do this or can I get away with items like steering wheel puller (I have not gotten this far to see if this is even an option), soft hammer, luck...???? BTW this is a 01 YZ250. Thanks
 
Joined
Jan 2, 2002
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#3
you are going to have to split the cases, it is not that hard just keep track of all the parts you have to remove first. when you split the cases the trans will be open and the shims and thrust washers will need to be kept in place on the shafts. if you do not have a service manuel get one! You will most likely need to replace the crank bearings. As far as the wrist pin soak it in PB Blaster and try heating the piston and rod, you can use a bolt that will fit inside the wrist pin and a larger socket on the other side with a nut to pull the wrist pin into the socket. this method will put no side load on the rod and the least amount of damage. HMMMMMMMM things you should do get a rad valve, have the porting cleaned up and rejet, you will be shocked how much power you will get and how wide the power band is. if you ride woods try a flywheel weight around 12oz works well. if you want even more hit fmf fatty and shorty silencer. be prepared the jetting will be way off on the main!
 
Joined
Jan 18, 2003
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#4
Is there any special tools that I will need to do all of this? I will definitly do the socket/bolt technic if I can't get the piston pin out with heat. Thanks for the tips.
 

bigc

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Joined
Jun 3, 2003
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#5
You will probely need a fly wheel puller to get the fly wheel off.Do not beat on it with a hammer.The crank will need to be pressed out and pulled back in when you reassemble the engine.You can get a tool to do this or make your own.I got some metric all thread and a steering wheel puller to press it out,I drilled a piece of flat metal or something to fit over the crank put the nut on and kept tightening the nut and using shims to pull it in.I am talking about the fly wheel side being pressed in,you should be able to just lay the engine on the side pull the other side off.This will leave you transmission all intact so you can remove all at once and don't have a zillion pieces to try and figure out where the go.I would definately get some crank bearing and seals and a complete gasket kit.I bought all my stuff from a place called tjparts exspress.It cost me about three hundred to completely do mine.Crank bearing,gaskets.bought a pro-x piston{it was the cheapest).also connecting rod and labor to get it pressed together $70.Hope this helped good luck!
 

bigc

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Jun 3, 2003
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#6
Hey one more thing when you go to put those crank bearings in put them in the freezer over night this will make them go in a little easier.Put them in the same way the old ones come out also.(numbers in out ect.)