Pressing crank bearings, correct methods?

[Jasle]

I am not a total amature of 2 stroke bottom ends. split upwards of 50 cases. In all that time I have pressed the bearings on the cold crank, put the crank and bearings in the freezer and after an hour or two I put the crank/bearigs assy in the motor without incident.
So in the last week 2 different people have commented that its better to put the crank bearings in the case halves first to avoid wedging them cockeyed in the case halves.
So I have known a few guys that have broken cases and I'm wondering which method is reccomemded buy others. I don't want to be buying someone a set of case halves!

Thanks In Advance...
Jason

 

[reelrazor]

I freeze the bearings, and heat the cases. The bearings basically fall into place. By the time you get the bearings in both cases, the temps have equalized and you can put the seals in.

I have acess to a lathe so I use that luxury to make aluminum slugs that fit the inner race of the bearings. These are about 2.5" long and can have a different size on each end. I make sure the cases are ready to go together, get the crank out of the freezer bag(ziploc'd please). I put the slug in the right side bearing and heat the high(farthest from the seal) end of it for a couple minutes with a propane torch, and then drop the crank in. Then I will apply sealer to the right case half and repeat the slug heating on the left bearing. That case will slide right on with nothing more than hand squeezing on opposing ends of the cases.

p.s. gimme the dimensions you need and I will turn these slugs out of 6061 aluminum for 12.95 plus shipping.

 

[Uchytil]

I do it two ways. One is to use a hyd press to push out the old mains and install the new mains. Another way I use is to heat the case half around the boss with propane and drop bearings in that were in the freezer for an hour or so. When I'm raedy to install the crank (it's in the freezed also for an hour or so) I insert an aluminum slug in the bearing, heat the slug and the crank drops right in. No forcing needed. SO, All you really need is a freezer and propane torch to get it together. I've never removed the old bearings w/o a press though. The slugs I make myself with a file and grinder. I don't have a lathe. I just cut away the meat of the slug with a hacksaw, grind, then file smooth, they almost look like they were turned on a lathe. The aluminum rod can be had at a local metal supply, they usually have scrap laying around. Question: How do ya'll get the old bearings out w/o a press? I'm hesitant about suggesting a slide puller although that's what I use for wheel bearings.

 

[Jasle]

so far I have not really had them stick in the case. I use a case splitter I made and the bearings stay on the crank. I've had to use some green loctite on a few occasions to get the bearings tight in the case...usually only if they had spunthe bearings or the bottom end had been apart tons of times. I work mostly on the 50 and 65cc race bikes...

 

[PINGERS4LIFE]

i use hammer and a socket to get the old ones out then i use a hammer and socket to put them back in i never had a problem just make sure when u put them back in use to outer race and not the inner

 

[darringer]

I also heat the cases and freeze the bearings. I have always put the bearings in the cases first. Never had any problems with assembly or alignment this way.

 

[Jasle]

I guess my biggest question with the heating of the bearing is will I melt my bearing spacers...ours are plastic. Thats why I freeze the crank with the bearings together.

 

[JasonWho]

Jasle, when you say, "ours are plastic", do you mean KDX200 or 50cc and 60/65cc bikes?

Thanks.

 

[Jasle]

Jasle, when you say, "ours are plastic", do you mean KDX200 or 50cc and 60/65cc bikes?

Thanks,
Jason, future left crankcase seal replacer, Who

yeah the small bikes mostly as thats what I'm working on the most.

 

[JasonWho]

OK, thanks!