Roller bearings VS Ball bearings for Crank bearings

hypermoto
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Bostwick, FL US
11/30/2020 7:57am
Hello,

I’m just curious as to the benefit of using a roller bearing for the stator side crank bearing. KTM, TM and maybe Beta? Use this setup.

I’ve always seen the ball bearing on the clutch side wear out quicker than they normally do on some KTM’s.

I guess my question is... why? And could you use 2 ball bearings instead? (Replace roller bearing with equivalent ball bearing?)
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kb228
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Mansfield, OH US
11/30/2020 8:55am
Simple answer is ball bearings are decent at both radial loads and thrust loads. Roller bearings are really good at radial loads but are horrible for thrust loads.

Replacing the roller bearing with a ball bearing would likely require a small ball type bearing which would probably be better with thrust loads but much worse in radial loads.

Because the flywheel and nut on the clutch side kindof keep everything from moving in the axial direction, thrust loads arent that high. Its radial loads that are important to look at. The logic behind using both is likely that the single ball bearing will handle the thrust loads and the roller bearing will increase the total radial load capacity of the set of bearings.
9
hypermoto
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11/30/2020 12:24pm
kb228 wrote:
Simple answer is ball bearings are decent at both radial loads and thrust loads. Roller bearings are really good at radial loads but are horrible for...
Simple answer is ball bearings are decent at both radial loads and thrust loads. Roller bearings are really good at radial loads but are horrible for thrust loads.

Replacing the roller bearing with a ball bearing would likely require a small ball type bearing which would probably be better with thrust loads but much worse in radial loads.

Because the flywheel and nut on the clutch side kindof keep everything from moving in the axial direction, thrust loads arent that high. Its radial loads that are important to look at. The logic behind using both is likely that the single ball bearing will handle the thrust loads and the roller bearing will increase the total radial load capacity of the set of bearings.
Was always curious about the design. Awesome explanation, thank you!!
silver753
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Brick, NJ US
12/1/2020 9:06pm
OEM KTM85's come with a roller flywheel side and ball bearing right side, but on the Wiseco bottom end kits (helping a buddy, not my first choice) it came with roller bearings on both sides. Worked great and his kid's been riding it for a couple seasons now.

And good, knowledgeable explanation kb228!
Tracktor
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12/2/2020 10:29am
silver753 wrote:
OEM KTM85's come with a roller flywheel side and ball bearing right side, but on the Wiseco bottom end kits (helping a buddy, not my first...
OEM KTM85's come with a roller flywheel side and ball bearing right side, but on the Wiseco bottom end kits (helping a buddy, not my first choice) it came with roller bearings on both sides. Worked great and his kid's been riding it for a couple seasons now.

And good, knowledgeable explanation kb228!
They have a roller both sides? That's scary. Nothing to hold the crank from floating which is a big issue on the KTM 85's. I always replaced the LH roller with a caged ball bearing on the numerous KTM 85 bottom ends I've rebuilt. Especially on the 17 -older ones which had to be shimmed to keep from having crank failures. I have a stack of roller bearings in a box never used from rebuilds, lol...........

The Shop

hypermoto
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12/2/2020 12:24pm
silver753 wrote:
OEM KTM85's come with a roller flywheel side and ball bearing right side, but on the Wiseco bottom end kits (helping a buddy, not my first...
OEM KTM85's come with a roller flywheel side and ball bearing right side, but on the Wiseco bottom end kits (helping a buddy, not my first choice) it came with roller bearings on both sides. Worked great and his kid's been riding it for a couple seasons now.

And good, knowledgeable explanation kb228!
Tracktor wrote:
They have a roller both sides? That's scary. Nothing to hold the crank from floating which is a big issue on the KTM 85's. I always...
They have a roller both sides? That's scary. Nothing to hold the crank from floating which is a big issue on the KTM 85's. I always replaced the LH roller with a caged ball bearing on the numerous KTM 85 bottom ends I've rebuilt. Especially on the 17 -older ones which had to be shimmed to keep from having crank failures. I have a stack of roller bearings in a box never used from rebuilds, lol...........
I’m asking cause I’m rebuilding both TM 144 bottom ends, 19 and 14, and the OEM stator side roller is over 100CAD while the other side ball bearing is $30. I’m just curious what the result would be if we used ball bearings on both sides. I probably won’t, but the idea/thought is there
WEAL
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DE
12/3/2020 5:08am
Rollers: you could use two rollers, one double shouldered, the other no shoulder or two rollers with a shoulder each but then check endplay when cold. When crank and case expand at different rates and the length difference is less of the sideplay of ballbearings you can get away with two ball bearings - just like the YZ250 does. This is not good engineering but still seems to work for a long time. The combination of ball and roller speeds assembling and thus no need for checking endplay.
karlz
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GB
12/3/2020 1:28pm
The roller bearing fitted makes the cases easier to split and and rebuild. You should not need a crankcase splitting tool.
Tracktor
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12/4/2020 11:23am
silver753 wrote:
OEM KTM85's come with a roller flywheel side and ball bearing right side, but on the Wiseco bottom end kits (helping a buddy, not my first...
OEM KTM85's come with a roller flywheel side and ball bearing right side, but on the Wiseco bottom end kits (helping a buddy, not my first choice) it came with roller bearings on both sides. Worked great and his kid's been riding it for a couple seasons now.

And good, knowledgeable explanation kb228!
Tracktor wrote:
They have a roller both sides? That's scary. Nothing to hold the crank from floating which is a big issue on the KTM 85's. I always...
They have a roller both sides? That's scary. Nothing to hold the crank from floating which is a big issue on the KTM 85's. I always replaced the LH roller with a caged ball bearing on the numerous KTM 85 bottom ends I've rebuilt. Especially on the 17 -older ones which had to be shimmed to keep from having crank failures. I have a stack of roller bearings in a box never used from rebuilds, lol...........
hypermoto wrote:
I’m asking cause I’m rebuilding both TM 144 bottom ends, 19 and 14, and the OEM stator side roller is over 100CAD while the other side...
I’m asking cause I’m rebuilding both TM 144 bottom ends, 19 and 14, and the OEM stator side roller is over 100CAD while the other side ball bearing is $30. I’m just curious what the result would be if we used ball bearings on both sides. I probably won’t, but the idea/thought is there
I've replace ball bearings in many KTM bottom ends & never an issue. BTW, if same as KTM bearings the ProX kits use good Japanese spec bearings for much less $$. Koyo/ntn etc...
Rickyisms
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12/4/2020 12:59pm
Tracktor wrote:
They have a roller both sides? That's scary. Nothing to hold the crank from floating which is a big issue on the KTM 85's. I always...
They have a roller both sides? That's scary. Nothing to hold the crank from floating which is a big issue on the KTM 85's. I always replaced the LH roller with a caged ball bearing on the numerous KTM 85 bottom ends I've rebuilt. Especially on the 17 -older ones which had to be shimmed to keep from having crank failures. I have a stack of roller bearings in a box never used from rebuilds, lol...........
hypermoto wrote:
I’m asking cause I’m rebuilding both TM 144 bottom ends, 19 and 14, and the OEM stator side roller is over 100CAD while the other side...
I’m asking cause I’m rebuilding both TM 144 bottom ends, 19 and 14, and the OEM stator side roller is over 100CAD while the other side ball bearing is $30. I’m just curious what the result would be if we used ball bearings on both sides. I probably won’t, but the idea/thought is there
Tracktor wrote:
I've replace ball bearings in many KTM bottom ends & never an issue. BTW, if same as KTM bearings the ProX kits use good Japanese spec...
I've replace ball bearings in many KTM bottom ends & never an issue. BTW, if same as KTM bearings the ProX kits use good Japanese spec bearings for much less $$. Koyo/ntn etc...
Didn't you have a gnarly piston failure with Pro-X? Do you still vouch for their bearings?
hypermoto
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12/4/2020 9:28pm
hypermoto wrote:
I’m asking cause I’m rebuilding both TM 144 bottom ends, 19 and 14, and the OEM stator side roller is over 100CAD while the other side...
I’m asking cause I’m rebuilding both TM 144 bottom ends, 19 and 14, and the OEM stator side roller is over 100CAD while the other side ball bearing is $30. I’m just curious what the result would be if we used ball bearings on both sides. I probably won’t, but the idea/thought is there
Tracktor wrote:
I've replace ball bearings in many KTM bottom ends & never an issue. BTW, if same as KTM bearings the ProX kits use good Japanese spec...
I've replace ball bearings in many KTM bottom ends & never an issue. BTW, if same as KTM bearings the ProX kits use good Japanese spec bearings for much less $$. Koyo/ntn etc...
Rickyisms wrote:
Didn't you have a gnarly piston failure with Pro-X? Do you still vouch for their bearings?
ProX bearings are Koyo, NTN, etc. Like he said (as good as any SKF bearing aeound). Any type of piston can fail
Davidzhz
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3/17/2024 8:50am Edited Date/Time 3/22/2024 4:05pm

Roller bearings handle radial loads better, ideal for the stator side with magneto drag. Ball bearings are good for axial/thrust loads, like the clutch side takes.
Personally i use Bearing MFG ball bearing and works perfect.

motomind00132
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3/17/2024 6:47pm
hypermoto wrote:
I’m asking cause I’m rebuilding both TM 144 bottom ends, 19 and 14, and the OEM stator side roller is over 100CAD while the other side...
I’m asking cause I’m rebuilding both TM 144 bottom ends, 19 and 14, and the OEM stator side roller is over 100CAD while the other side ball bearing is $30. I’m just curious what the result would be if we used ball bearings on both sides. I probably won’t, but the idea/thought is there
Tracktor wrote:
I've replace ball bearings in many KTM bottom ends & never an issue. BTW, if same as KTM bearings the ProX kits use good Japanese spec...
I've replace ball bearings in many KTM bottom ends & never an issue. BTW, if same as KTM bearings the ProX kits use good Japanese spec bearings for much less $$. Koyo/ntn etc...
Rickyisms wrote:
Didn't you have a gnarly piston failure with Pro-X? Do you still vouch for their bearings?

Ive seen every single brand of low hour piston and valve fail before. Change parts on enough bikes it's not a matter of if you get a failure from a bad part it's when. Seen a brand new 09 yz250 getting warmed up before the customer took it for a spin and loaded up. Piston disintegrated right there with minutes on it. Ive got a hot rods rod in a built 270f with over 300 hours on it we're runing it until its out of spec or blows. Just new bearings nothing else during bottom ends. Shit just happens. 

Rickyisms
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3/17/2024 7:34pm
Tracktor wrote:
I've replace ball bearings in many KTM bottom ends & never an issue. BTW, if same as KTM bearings the ProX kits use good Japanese spec...
I've replace ball bearings in many KTM bottom ends & never an issue. BTW, if same as KTM bearings the ProX kits use good Japanese spec bearings for much less $$. Koyo/ntn etc...
Rickyisms wrote:
Didn't you have a gnarly piston failure with Pro-X? Do you still vouch for their bearings?
Ive seen every single brand of low hour piston and valve fail before. Change parts on enough bikes it's not a matter of if you get...

Ive seen every single brand of low hour piston and valve fail before. Change parts on enough bikes it's not a matter of if you get a failure from a bad part it's when. Seen a brand new 09 yz250 getting warmed up before the customer took it for a spin and loaded up. Piston disintegrated right there with minutes on it. Ive got a hot rods rod in a built 270f with over 300 hours on it we're runing it until its out of spec or blows. Just new bearings nothing else during bottom ends. Shit just happens. 

That post is over 4 years old… but it’s no secret Pro X is not what it used to be. 

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