main bearings

[SnapperD]

what's goin' on guys? i recently bought a used motor for my '02 yz 250 off of **** and am rebuilding it. i've already split the cases on it and pulled the crank out. my question is, is there any way to get the old main bearings out and the new ones in without an actual bearing press? any thoughts or ideas would be greatly appreciated.

 

[Zenith]

I'll probably be dubbed a red neck, but I've always removed main bearings by heating the case around the bearing with a blow torch, then using a drift of some sort on the inner race of the old bearing to drive it out. They tend to come out quite easily.
Stick the new ones in the freezer the night before fitting them (this will shrink them) and heat the case around where the bearing will be going in (this will expand it). Now you need something BIG to sit on the outer race of the bearing so you can drive it in. I have a large socket (something like a 2") that I use. I just use this and a copper mallet to drive the bearing in. I've done quite a few sets like this. Just use some common sense with regards to heat and force, if you're swinging the hammer over your head it's too much force!

 

[QKENUF4U]

zenith is right. just watch hitting that bearing. if you have the bearings cold enough and the case hot enough they should just drop in.
good luck

 

[SnapperD]

well, i popped 'em out last night. it just took a little more swing in the hammer than i was comfortable with, but was reassured by somebody who had already done it that way that it was necessary to use that much force. it was just a little discouraging when i put the case half in a vice and had all of my body weight on it (210lbs), and then some and they still weren't budgin'. i left the new ones in the freezer for a few hours and used the old bearing to hammer in the new ones. i 'preciate all the advice.