Trail ReportsTech ArticlesVideo GalleryHOME

Dec 6, 2008

Dirt Bike Bottom End Rebuild, Part 3, CR250

After removing the crank I could clearly see what was making all the noise. The bearing had actually come apart leaving pieces in the case. To hear what this sounded like while it was still running see part 1. Luckily, I think I caught it before it destroyed too much of the case or any other parts that I won't be replacing anyways. In part 2, I disassembled the engine up until the point where I needed to split the case. The video included below will detail the process of splitting the case, removing the crank and bearings and installing the new crank and bearings. I have also included a few pictures to show how it all goes back together.

Here is another shot of the carnage. The bearings were extremely pitted as well as the obvious destruction seen here. You definitely want to catch a problem like this before it gets this bad if you can. I have known that the bottom end was going bad for a while, but put off the rebuild a little too long. The signs include excessive smoke and spooge at the exhaust from burning gear oil, the noise as described above, and having to add gear oil excessively.

Here are a few pictures of the installation. Make sure the transmission is installed as shown with the forks in the correct grooves of the shift drum. Assembling the parts on the other side of the drum is tricky, you'll want to install the shift lever temporarily at this point to make sure you can shift through the gears, then install the outer clutch basket etc. in reverse order of how they came off.

PART 4, before and after video


  1. that is classic, nice pictures. I dont have the know how to rebuild my bottom end for my bike, but this certainly helps,

  2. I noticed "weird" problem with Wiseco crankshaft. I believe, that crankshaft gear must be closed tight?

    In my CR250R -98 there's about 0,20-0,30mm "free space" between bolt and gear.... and also gear is moving on the crankshaft.