Vintage Dirt Bike Q & A

Anybody have words of wisdom for this? Rebuilt the lower end, very careful prep and handling of the cases. Pressed in new bearings by heating the cases and gently tapping in the bearings. New seals. Crankshaft in the right case half and trans cluster in the left one. All of the thrust washers are in place. (I did not need to dis-assemble the shafts) Button it up and here's the deal. Countershaft spins freely, transmission shifts through the gears but the main shaft feels very stiff. I can turn the main shaft by hand but it is by no means as free as the countershaft. This stricks me as odd. I've build a few 125 lower ends and never had a problem; this is my first 250 effort. In retaliation i resplit the cases 3 times, pulled the gearsets, rubbed my forehead thoughtfully, and re-installed. Same result. I giving it a rest for now; the low end sits on my work bench with a smug look on it's cases. Thanks for any suggestions from the elsinore nation. Joe

Joe,

With the cases split and the gear sets installed, does the mainshaft turn easily?
If so, I suspect one of the mainshaft bearings is not completely seated. To
verify, put everything together like a normal assembly (you can leave the crank
shaft on the table for this one). As the cases come together, leave a small gap
between the halves (1/16"). Now rotate the main and countershafts. If
everything rotates freely, it's either an extra thrust washer or one of the bearings
needs to be "pounded" in. Heat the case again and give the bearing some carefully
measured wacks with a driver and hammer until you get that seated sound.

Also, I like to put all the "inards" in the right side case, then assemble using a crank
installer. It's easier to keep everything alligned that way.

dogger

_________________
1973 CR250M
1979 CR250R
1993 CR250R
2008 CR500R
2009 CR250R

Thank you sir, I have a fresh center case gasket coming and I'll let you know how that worked. I actually got the same story in conversation with Bill Clem of Cycle Stop Racing on the left coast; another reliable source of elsinore knowledge. Thanks again,,,,