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Inserting main bearings. Help!


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Hi,

 

I'm currently trying to install the main bearings and I've come across some problems:

 

I tried heating the cases in an oven at 170 deg C (340 F). The gear box bearings fell out, but the main bearings I had to tap a little bit. When I tried to install the new ones (which i had freezed down) they stopped half way in and wouldn't move. I then reheated the casings and took the main bearings out with some tapping. 

 

SInce I had to tap the new bearings on the inner race, can they be damaged from this? Should I buy new ones?

 

What temperature do you guys heat the cases to? I'm afraid the seals will melt if I go any higher (there are some bearings with seals on which I'm not planning to replace.

 

Please help me here,

 

Thank you,

 

-espkul

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I usually only go to around 250 or just a little more, but leave it in for at least 20+ mins to heat the whole case half evenly. How long did you heat them for? I hate to be Captain Obvious, but it's never a good idea to tap on the inner race of a bearing that you're gonna use. Also, since you have it apart, why not replace all the bearings? I've done it before too tho(still not a good idea AND you already have it apart so...). I usually freeze bearings overnight(dry ice and a cooler would be even better, but...) and have found that if the bearing doesn't tap in pretty easy from the outer race, then you prob need it hotter(not 350 tho). Did you tap them out and then try replacing them without letting the cases cool down and then reheating them for the install? I'm no professional, but I do have a lot of 2 strokes and that's how I do it. Good luck

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If the bearing still spins freely on you finger, it's alright. Get a socket or piece of pipe the size of the outer race of your crank bearing and a hammer ready. Heat/cool your parts, put a bit of grease on the outer bearing race, and smack it in quick. Don't fool around with "tapping", get it in there quick before your parts warm/cool toward the same temperatures.

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Thank you guys, this forum helped me out yet again!

I did not heat them between removal and inserting the bearings, and the bearings were probably not cold enough. I put them in the freeezer overnight

Now they just dropped right in. I just hope I didnt broke the bearings after tapping the inner races yesterday...

Edited by espkul
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Sweet you did it. They should just drop in. Right to the bottom and lay flat. Use a suitable glove, line it up carefully and drop it. A little oil on the outside of the bearing race can help.

 

I heat that area of the case with an electric heat gun.  Does it so fast that the rest of the case half doesn't get real hot. So no risk to any seals.  I assume most people use a flame torch.

 

I never considered putting a case half in the oven. That'd mean carrying it to the garage.   Which just seems like more work, plus I could trip over our dog and I'm paranoid about damaging the case join surfaces. Besides, my wife would go nuts with the smell.

 

Chances are good that your bearing is just fine. Assuming it's a high quality part.

Edited by numroe
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