Jump to content
Sign in to follow this  

I need Help on doing my first bottom end on a 250f

Recommended Posts

I just bought a 2002 Yz250f and am the third owner. The bike is in excellent shape on the outside and ran great. This is my first four stroke and with hearing all the horror stories about expensive rebuilds I decided to check out the top end and cam gear on the crank. The top end checked out pretty good and am having the valves lapped in. I had planned on replacing the piston, rings, pin, bearing and cam chain. My problem arose when i checked the cam gear on the crank and it is worn pretty bad. I need to relace the crank and haven't done a bottom end before so i would appreciate any tips or tricks you guys have learned along the way as well as what else to look for when i have it apart, gears, shift forks etc. Also it necessary to have a puller to split the case or can you heat it.Thanks

Share this post


Link to post
Share on other sites

The case should split relatively easy...You will need a special flywheel puller though, but what I usually do is once I get the motor down to that stage where the flywheel is ready to come off, I bring it into a Yamaha dealer and they pop it off for me...But just remember how everything came off, take pictures if you want, and if you dont have a manual, it is a must...Good luck..

Share this post


Link to post
Share on other sites

I don't know about the bottom end (in fact, I just got my motor back today from dealer, they had just the motor, no top end. They replaced my crank for 225) The top end is really easy though. Working on it from about 6:30 to now I have the motor together. Has compression so thats a good sign!

-Phill

Share this post


Link to post
Share on other sites
I just bought a 2002 Yz250f and am the third owner. The bike is in excellent shape on the outside and ran great. This is my first four stroke and with hearing all the horror stories about expensive rebuilds I decided to check out the top end and cam gear on the crank. The top end checked out pretty good and am having the valves lapped in. I had planned on replacing the piston, rings, pin, bearing and cam chain. My problem arose when i checked the cam gear on the crank and it is worn pretty bad. I need to relace the crank and haven't done a bottom end before so i would appreciate any tips or tricks you guys have learned along the way as well as what else to look for when i have it apart, gears, shift forks etc. Also it necessary to have a puller to split the case or can you heat it.Thanks

The cases will split relatively easy. Warm up one crank bearing with some propane, and use a rubber mallet to start working the cases apart. It's not a super tight press fit crank to bearing. I just did a complete 250F rebuild, and it's VERY challenging. There is a MILLION O-rings and dowel pins inside the engine. Draw pictures, and place the o-rings and dowels inside small bags and label them. When you go to assemble the engine, trust me, you won't remember where each tiny component goes. I had to re-dissasemble my lower end TWICE because of forgotten parts. Good luck, and DONT RUSH the rebuild!!

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

Sign in to follow this  

×
×
  • Create New...