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October 1st, 2015, 08:10 PM   #111
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Best way to remove the main bearings?

I've got some aluminium round bar, large enough to machine some bearing presses...

Tried baking the left half of the case in the oven at 275f for an hour, and using a socket to hammer the bearing out, but it wouldn't budge.

What about the right half? The hole is even smaller.

I've heard of welding a shaft into the race (to shrink the race)... but I don't have easy access to a welder unfortunately.
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October 2nd, 2015, 08:21 AM   #112
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I know it's probably not best practice, but here's what I did.

Remove the rollers and cage from both bearings. Lightly gas torch the area around the bearings, starting close to the outer race and circling to the edge of the crank gallery. I was concerned I was going to heat warp the cases so i did this slowly.

It took about 15mins per case and it still wasn't all that hot, I'd think about 120c by the way water just sizzled on it.

Then I took an eye dropper and squirted cold water into the races to cool them a bit. This might not have helped, but I did it anyway. Working quickly I then took a screwdriver and lightly tapped at the lip of the outer race in a star pattern. The left race came out easily, I repeated the process twice for the right.

Sounds like you have tight cases, give it a go it might help.
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October 2nd, 2015, 09:35 AM   #113
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I'll machine my bearing presses first, then bake the cases, and use the tools I make.

I'll try without heating the cases first... I probably didn't hit the bearing very hard because I'm not big on smashing things with hammers.
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October 2nd, 2015, 03:53 PM   #114
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I use 320F on hard ones it takes about 40 min in an oven to get there, you'll notice the oil reallly starts baking off toward the end

the roller bearings will just fall out after that, if there are ball bearings they can be very tight and need a drift and a big hammer, a press is better if you have one but its tricky with the hot case
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October 2nd, 2015, 06:33 PM   #115
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Originally Posted by bushmechanic View Post
Johns thread is full of good info but i noticed the last few pages have some people wondering what to do.

viewtopic.php?f=5&t=6195

the ideas here are not just my opinion, there are a great many good minds who have worked out what causes the failures and even better have tried a number of different solutions. the majority of these solutions are scattered through KTM talks RFS section.

what causes the oem roller bearings to fail ?

1) crank spread under its own weight is the main problem

2) misalignment of the bearing bore, seems rare, search lineaweavers posts

3) insufficient crank axial play (end float) with crank spread

what is crank spread?

when the crank spins, its own weight causes it to spread outward opposite the pin
when you add in the combustion forces they contribute further to the spread.

sorry for the crappy pic there is a better one i will add later



in this condition while running the axial play of the crank reduces until the forces deforming the crank outward are matched by the crank resisting deformation (a function of its stiffness)

if you don't have enough end float or stiffness for the weight of the crank and the rpm its doing your end float (axial play) will become zero

with zero axial play the NJ series roller bearings will experience side loads as they are now subjected to some of the force causing crank spread
well explained Bushy, may I add Bearing skid, when the NJ bearing has side load it stops the rollers in the bearing rolling and they skid around the inner race wearing it away.
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October 2nd, 2015, 08:05 PM   #116
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Originally Posted by bushmechanic View Post
I use 320F on hard ones it takes about 40 min in an oven to get there, you'll notice the oil reallly starts baking off toward the end

the roller bearings will just fall out after that, if there are ball bearings they can be very tight and need a drift and a big hammer, a press is better if you have one but its tricky with the hot case
So I should try 320F for 40 minutes, and see if the rollers nearly "fall" out?

Might save me some time....

I kind of didn't want to replace the counter-balance shaft bearing though, it's double sealed, and I'm not worried if any metal got chewed up in it...

The woodruff keys are VERY tight in the shafts... kind of didn't want to disturb that one in particular because of it.
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October 3rd, 2015, 12:21 AM   #117
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Ta John yes I agree, definitely skidding rollers is the cause of the damage and yes caused by excessive side (axial) loads which prevent the rollers turning freely

borg i reckon if they don't fall out after that tap the case onto a bench if still not falling out use a drift

FWIW the countershaft bearing usually has junk in it even with the seals it worth cleaning if not replacing
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October 3rd, 2015, 06:44 AM   #118
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Are we talking about the same bearing?

The one that the gear for the counter-balancer drives, and has the water pump also driven off of it?

I don't want to wreck the woodruff key, it's in there extremely tight... I tapped on it with a drift, and it didn't budge.
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October 3rd, 2015, 08:05 PM   #119
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yes same bearing
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October 5th, 2015, 10:11 AM   #120
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Has it been asked before - What happens with too much axial play?
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