Roller bearings VS Ball bearings for Crank bearings

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11/30/2020 7:57 AM
Edited Date/Time: 11/30/2020 7:58 AM

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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11/30/2020 8:55 AM

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.

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11/30/2020 12:24 PM

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 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!!

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12/1/2020 9:06 PM

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!

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12/2/2020 10:29 AM

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 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...........

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12/2/2020 12:24 PM

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 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 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

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12/3/2020 5:08 AM

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.

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12/3/2020 1:28 PM

The roller bearing fitted makes the cases easier to split and and rebuild. You should not need a crankcase splitting tool.

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12/4/2020 11:23 AM

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 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 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 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...

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12/4/2020 12:59 PM

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 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 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 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?

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12/4/2020 9:28 PM

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 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 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

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