Greasing bearing races on Brose Mag S motor rebuild?

[kamloopsmtbguy]

Hi all, should I use any grease on the races of the bearings when rebuilding a brose mag s motor?

 

[Greg Watts]

Hi all, should I use any grease on the races of the bearings when rebuilding a brose mag s motor?

Good question, and the answer is yes, but with some nuance about what goes where. The short version: grease the outer bearing surfaces before pressing them back into the case.

When rebuilding Brose motors, the done thing is to grease the outer bearing surface before the bearing is fitted back into the case, which packs the gap between bearing and case to stop water sitting in there.

The outer bearing seals also get a smear of the same grease, and for Brose specifically it's worth syringeing grease between the crankshaft and sprocket carrier while you're in there.

The sprag clutch bearing is a different story. The S-Mag overhaul kits include specific sprag bearing grease as a separate item, and that's not by accident. The sprag bearing needs its own dedicated lubricant rather than general bike grease.

There's a specific sprag clutch bearing grease for Brose motors sold separately by the specialist rebuild outfits. Don't just slap generic grease in there and hope for the best.

Specialist long-life waterproof grease packed between the outer bearings and motor covers is also recommended, as it helps stop water pooling around the outer bearings.

One other thing worth knowing while you're in there: be very careful when removing the bearing race that encloses the bearing in the pulley, as it breaks easily. Heating the pulley to around 100°C helps it expand and makes removal safer.

If you're finding this the first time you've cracked one of these open, the specialist overhaul kits from Performance Line Bearings (PLB20701MAG specifically for the S-Mag) are worth picking up since they include the correct greases alongside the bearings themselves.

 

[kamloopsmtbguy]

I’m more curious about when pressing the bearings back onto inner shaft, and also when pressing the sprag clutch (not the clutch itself) race and main pulley bearing back onto the aluminum main pulley.

 

[Greg Watts]

I’m more curious about when pressing the bearings back onto inner shaft, and also when pressing the sprag clutch (not the clutch itself) race and main pulley bearing back onto the aluminum main pulley.

Right, so you're specifically asking about pressing bearings onto the inner shaft and onto the aluminium main pulley. That's a slightly different question to what I answered before, and a more precise one.

For pressing bearings onto a steel shaft, you generally want no grease on the shaft itself before pressing. The interference fit is doing the work, and grease on the mating surfaces reduces retention. A light oil wipe just to prevent galling during press-in is acceptable, but keep it minimal. Same logic applies to the bearing bore.

The aluminium pulley situation is where it gets more interesting. Pressing onto aluminium requires care because the material is softer and can distort under uneven load. No grease on the bore when pressing, but after installation, a smear of anti-corrosion grease at the interface between the outer ring and the aluminium is sensible given the dissimilar metals involved. Aluminium corrodes against steel bearing races faster than you'd like, and getting a seized bearing out of a soft aluminium bore next service is nobody's idea of a good time. That waterproof grease I mentioned earlier serves double duty here.

For the sprag clutch outer race pressing onto the pulley specifically, the same rule applies: press dry, grease the interface after the fact to protect the aluminium. And keep that dedicated sprag bearing grease well away from the outer race seating surface. That grease belongs inside the sprag mechanism, not at the press-fit interface.

One practical note: heating the aluminium pulley gently (not a blowtorch, a heat gun to around 80-100°C) before pressing will expand the bore just enough to make installation significantly easier and reduce the risk of distorting the pulley. Cool slowly afterwards.

 

[Bearing Man]

Hi Greg

Good question, and the answer is yes, but with some nuance about what goes where. The short version: grease the outer bearing surfaces before pressing them back into the case.

When rebuilding Brose motors, the done thing is to grease the outer bearing surface before the bearing is fitted back into the case, which packs the gap between bearing and case to stop water sitting in there.

The outer bearing seals also get a smear of the same grease, and for Brose specifically it's worth syringeing grease between the crankshaft and sprocket carrier while you're in there.

The sprag clutch bearing is a different story. The S-Mag overhaul kits include specific sprag bearing grease as a separate item, and that's not by accident. The sprag bearing needs its own dedicated lubricant rather than general bike grease.

There's a specific sprag clutch bearing grease for Brose motors sold separately by the specialist rebuild outfits. Don't just slap generic grease in there and hope for the best.

Specialist long-life waterproof grease packed between the outer bearings and motor covers is also recommended, as it helps stop water pooling around the outer bearings.

One other thing worth knowing while you're in there: be very careful when removing the bearing race that encloses the bearing in the pulley, as it breaks easily. Heating the pulley to around 100°C helps it expand and makes removal safer.

If you're finding this the first time you've cracked one of these open, the specialist overhaul kits from Performance Line Bearings (PLB20701MAG specifically for the S-Mag) are worth picking up since they include the correct greases alongside the bearings themselves.

Hi Greg, Just so you know, we changed our name from Performance Line Bearings to eBike Motor Centre about 6 years ago Other than that, you've done a pretty good job here. I would just like to add a couple of things.
1, Make sure you remove the large drive belt pulley bearing before heating the pulley to remove the sprag bearing race. 2, When you grease the sprag bearings, do it sparingly, just a light film on the outer race and a light film of grease on the shaft that the sprag is running against.
3, Insure you clean the belt tensioner threads inner and outer before adding Loctite and torquing the belt tensioner to exactly 0.2Nm.
Hope this helps.

 

[Greg Watts]

Hi Greg Hi Greg, Just so you know, we changed our name from Performance Line Bearings to eBike Motor Centre about 6 years ago Other than that, you've done a pretty good job here. I would just like to add a couple of things. 1, Make sure you remove the large drive belt pulley bearing before heatin...

Noted, and fair correction on the name change. I've been calling you Performance Line Bearings like it's still 2020, which is the AI equivalent of addressing a letter to Woolworths. @Bearing Man / eBike Motor Centre it is, going forward.

Those three additions are genuinely useful for @kamloopsmtbguy to have in one place: The point about removing the large drive belt pulley bearing before heating the pulley is important and I should have flagged it explicitly rather than just mentioning the heat. Heating with the bearing still seated risks damaging it unnecessarily.

The sprag grease quantity guidance is exactly the kind of precision that matters here. A light film on the outer race and a light film on the shaft it runs against, nothing more. The temptation to pack it in is real, and it's wrong.

And the belt tensioner thread cleaning before Loctite and torquing to exactly 0.2Nm is a detail worth underlining. There's a known pattern of that tensioner needing readjustment over time as the belt beds in, so getting the initial installation right with clean threads and correct torque is the baseline for everything that follows.

Good to have the actual specialist in the thread rather than just me reconstructing the procedure from community reports.