Bosch Gen4 Seal Service & Grease up
- Thread starter RustyMTB
- Start date
Don't be disheartened guys, the industry is changing. Looking at the latest motors coming out, they are becoming way better protected than they used to be. We are starting to see more sealing solutions on many of the new motors. However, sealing against a determined person with a pressure washer will always be a big challenge.
It may have helped me make the decision at the time to up my budget to a Bosch bike yeah..This thread might have helped had you bought a Bosch bike though
Hey @Bearing Man is there a reason the new kit uses sintered bronze bushing? is the surface pressure to high for a self lubricating plastic one?
Yes, although this part of the motor is only supporting the riders weight, and pedal power, it also has to deal with jumps, crashes and pedal strikes. The loading from from these could destroy most plastic or fibre bushes.
I did that this year to my 2020 Bosch CX.
I heard a weird sound coming from the motor area. After 20K km(+/-) I thought …this is it, time for a serious service. I removed the motor, packed it up, and sent it to CycloChrome in Hull, Que. (One of Pete’s service centres).
While I was removing the motor I noticed that the castle nut(holding the chainring) had become loose. (And likely the noise I heard). I removed the castle nut several times before for “cave” service and installing the bearing seal kit.
What I discovered is the castle nut can become loose after several removals and the fine threads on the castle nut may stretch or distort. I read somewhere that this retaining nut (castle or spider nut) should be replaced with a new one. Also that the torque has been increased to 35nm for a specific type of new nut. It seems fairly common that this castle nut becomes loose,(and a few solutions have been posted) but a new upgraded castle nut with slightly higher torque (35nm) seems to solve the problem. A new nut is about $6-$12. I keep a spare, or two.
Hey @Bearing Man
Getting ready to overhaul the motor over the weekend and I would like to check if I have everything:
-white motorex grease for the gears?
-green motorex grease for the outer seals and the between the both shafts?
-does the one way clutch use any specific grease?
-what are the tube dimension used to pull the clutch off?
-should the clutch come of with force (the puller tool)? shouldn't the needle bearings release the shaft at a certain orientation so it comes of with no force?
-IPA to clean the pcb and connectors?
-do i need to reaply new (blue) thermal compound for the transistors?
Thanks!
Getting ready to overhaul the motor over the weekend and I would like to check if I have everything:
-white motorex grease for the gears?
-green motorex grease for the outer seals and the between the both shafts?
-does the one way clutch use any specific grease?
-what are the tube dimension used to pull the clutch off?
-should the clutch come of with force (the puller tool)? shouldn't the needle bearings release the shaft at a certain orientation so it comes of with no force?
-IPA to clean the pcb and connectors?
-do i need to reaply new (blue) thermal compound for the transistors?
Thanks!
My ebike is a 2023 Moterra Neo 3 , 1 year and 9 months and 7100Km and I mainly ride in Mediterranean dry climate, but I also make trips to the wetter northern Spain and spend a week riding there.
In preparation for another trip, I decided to re-grease the seals, and I found that the seals are in very good shape, with very little grit and there still is some of the original grease, and the crank bearings do not show any sign of rust.
After reading all the experiences here, the process went very well, I found that it was easy to remove the black rubber and metal seal, the only requirement is to insert the plectrum under the black rubber ring, and NOT under the yellow seal.
I also found that the crankarm caps and the chainring nut torque were far below the specs of around 40NM for the caps and 35Nm for the nut, so I am lucky that I did not have problems.
In preparation for another trip, I decided to re-grease the seals, and I found that the seals are in very good shape, with very little grit and there still is some of the original grease, and the crank bearings do not show any sign of rust.
After reading all the experiences here, the process went very well, I found that it was easy to remove the black rubber and metal seal, the only requirement is to insert the plectrum under the black rubber ring, and NOT under the yellow seal.
I also found that the crankarm caps and the chainring nut torque were far below the specs of around 40NM for the caps and 35Nm for the nut, so I am lucky that I did not have problems.
Do you think that Muc Off bio grease I have lying around is good enough for around the crankshaft? Or if something thicker would be better. I can't find any info what kind of grease is that Muc Off.
Also is the guitar pick really needed? Can I damage the seal by using a metal pick or knife for example?
Also is the guitar pick really needed? Can I damage the seal by using a metal pick or knife for example?
The guitar pick wants carefully sticking in the bin
I always use a Stanley knife blade for prizing bearing seals off.
As for the grease, I've no idea on the muc off stuff but it's only really external on the motor and it must be better than nothing
I used this grease, and it looks exactly like the Bosch grease:
motorex.com
FETT 2000
Grasa de jabón de calcio increíblemente adhesiva con un alto nivel de resistencia a la oxidación. Presenta una excelente resistencia al agua y una excelente capacidad de soporte de presión. Esta grasa de larga duración se puede utilizar en todos los puntos de los rodamientos expuestos a...
motorex.com
HEY! You can sell those guitar picks after use…C’mon man.The guitar pick wants carefully sticking in the bin
I think a really thick grease in that area is mostly to keep debris and moisture away from the crank bearing. A new seal also helps.I used this grease, and it looks exactly like the Bosch grease:
FETT 2000
Grasa de jabón de calcio increíblemente adhesiva con un alto nivel de resistencia a la oxidación. Presenta una excelente resistencia al agua y una excelente capacidad de soporte de presión. Esta grasa de larga duración se puede utilizar en todos los puntos de los rodamientos expuestos a...
Needed a holiday so have neglected my duties for a while! Sorry if this is late but it still may help.
To answer your questions:
-white motorex grease for the gears? No! Bosch had their gear grease specially formulated to do all the different jobs required of it in that one motor. It is also safe for the PCB, seals and sprag bearing. This grease is currently not available to buy.
-green motorex grease for the outer seals and the between the both shafts? Yes, no problem for the seals, but do not use it to grease in between the crankshaft and the torque tube (metal sleeve over the crankshaft). If this is greased it will produce too much drag which may cause the motor to run on and keep driving after you stop pedalling.
-does the one way clutch use any specific grease? Yes. We supply this free of charge with our bearings and kits.
-what are the tube dimension used to pull the clutch off? We also sell the special tool required to remove and refit the drive gear easily.
-should the clutch come of with force (the puller tool)? shouldn't the needle bearings release the shaft at a certain orientation so it comes of with no force? This may happen if you're very luck. Normally, it will pull the sprag bearing out of the gear by distorting and pulling off the lower retaining ring.
-IPA to clean the pcb and connectors? Yes. We would also treat with Corrosion X.
-do i need to reaply new (blue) thermal compound for the transistors? Technically yes. However, if you are in a cooler, relatively flat country, you will get away with it. If you want to go up a mounting in death valley, I would replace it.
Thanks!
-So what do I use if the gear grease needs replacing?
-what do you recommend I use in the torque tube to inhibit corrosion? Thin layer of grease or oil?
-can you link to the puller tool?
-doesn't the pulling damage the teeth in the sprag clutch? what is the purpose of a dual clutch in the gen4 (sprag + ratchet clutch)? Is it expected to go back on the shaft with high force too (when using the mounting tube)?
-can you recommend a specific thermal compound?
Best regards
When I saw this I was curious about my Kiox. So I checked it this morning before my ride.
I don’t usually set the page to distance travelled, but these numbers made me laugh.
it’s almost identical to yours (except the miles/km thing).I mounted the Kiox to the top tube on the Rail with another type of mount which helped cleanup the cockpit. For almost 5 years it’s been through all types of weather. I’m surprised that the Kiox and controller is still working after all these years. What are we doing right?
Tone461
Active member
Some impressive mileage there guys......good to see
Hi @Bearing Man, there is available in your web a Bosch gear grease but intended only for Gen 1, 2, 3 and looks like Bosch has not made available the grease for Gen4 internal gears.
Then which grease would you recommend? Molykote PG-75 or other?
Last edited:
onek00lj4y
New Member
- Feb 24, 2026
- 6
- 18
You have to drop the motor to do this correctly as you can not clean it out properly or set the drain hole at 12 o'clock postion for drainage and make sure its not blocked,you can only do this my dropping the motor otherwise its only half a Job done!
Ken
Member
Hi Rusty, inspired by your seal grease vid a couple of years ago and re greased the seals on my Stilus back then.
Just completed a second regrease but this time replaced the large circlip on the chainwheel side with a circlip as in the pic complete with plier holes. Needed a small amount ground of, one side shown, but a perfect fit and only £3.90 for 2. The original O ring with flats was a bitch.
I am puzzling now about the orientation of the yellow O ring which sits inside the seal. Does it fit groove out or groove in??? I see you have it groove in but my logic tells me it should be groove out to sit up against the internal fixed O ring filled with grease. Any confirmation appreciated.
- Thread starter
- #172
I've always done it groove inwards as that was how it came off the first time I did it & so I assumed that's how it was assembled at the factory. Maybe @Bearing Man knows better?
Basically, you've nailed it! The groove holds the grease to lube the seal and any grit that makes its way behind the seal gets trapped before making it into the bearing.
