Bottom End Rebuild

[NOAHCAPELING18]

Ok so I'm rebuilding the bottom end in my 1997 Yamaha YZ80 and I am in the reassembly process, but I have made the mistake of putting the bearings onto the crank out of the case instead of in the cases first, and now can't get them off the crank....will it be ok to put the crank in with the bearings on it already? Also I don't have a crank installer so I was going to use a press to push it down into the case...ok/not ok??

[MaybeMe]

I wouldn't recommend it at all to use the crank to install bearings. You risk damaging them if they aren't installed with even pressure on the side, and could damage them, leading to accelerated wear on the bearings and crank.

[Tryingoutdirt]

you could pop the crank assembly in the deep freeze for a day or two and them when you got everything all ready to put the cases together have the cases sitting someplace nice and warm even like in front of a heater vent and  they will go together a bit easier.

[NOAHCAPELING18]

you could pop the crank assembly in the deep freeze for a day or two and them when you got everything all ready to put the cases together have the cases sitting someplace nice and warm even like in front of a heater vent and  they will go together a bit easier.

Ok thank you both and will freezing the crank and bearings, because of the temperature change will it speed up wearing as well??

[Beau 88]

Ok thank you both and will freezing the crank and bearings, because of the temperature change will it speed up wearing as well??

No it only contracts the size of the bearings when extremely cold , and expands the metal cases when heated so the bearings fit in easier . you do have to do it pretty quickly though . Some even put there cases in ovens at 150* or so or heat with a torch but risk fatiguing the aluminum cases at real high heat just don't over do it. I personally would rent a bearing puller ( autozone ) and pull those bearings back off the crank . Only pull on the inner race and no hammering 

[NOAHCAPELING18]

Ok thanks for the advice guys! ?

[MaybeMe]

My uncle said it's pointless to freeze bearings since it makes a miniscule difference, but everyone recommends it.

[Jdunn217]

Possibly try this?

http://m.harborfreight.com/large-bearing-separator-3979.html

[05CRF250]

To remove those crank bearings you will need a bearing splitter not a puller.

You don't need to remove the bearings but I suggest warming the cases with boiling water and put the crank in the freezer for a day. It should drop right in, if it needs a slight tap, just use a soft mallet on the crank ends to seat the bearings.

[NOAHCAPELING18]

Ok I don't have a bearing puller unfortunately ? I think im going to try putting it in the freezer and lightly heating up the case...that sounds like my best option....

[Jdunn217]

Ok I don't have a bearing puller unfortunately ? I think im going to try putting it in the freezer and lightly heating up the case...that sounds like my best option....

I posted a link where you could buy one for $30. You can probably find one cheaper if you search around on ebay for a little bit. Having the proper tools will make your life a whole lot less stressful, and allow you to do the job the right way. I have seen videos where crank bearings practically drop in after doing the heat and freeze method so that may work as well. Hope it works out for you either way!

Edited May 1, 2014 by Jdunn217