Old topic. Bosch Gen 4 motors

[TDM Cube]

Hi all, my first message so please be gentle! Riding a Cube action emtb on a regular basis with my two mates for just under four years. The ever increasing cost of consumables (tyres, pads, chains, etc) is a concern but I get that the extra power from the motor does make things wear out a bit quicker. The real issue is the reliability of the Bosch gen 4 motor. Reading posts this is an issue that has gone on for years. My first motor failed after 2.5 years Bosch did a "goodwill deal" and offered 50% off. The replacement motor lasted 13 months and this was replaced under warranty December 2024. I now have 11 months warranty left. If it fails after this time its going to cost close to a £1,000.00. Am I unlucky? One of my mates "Trek and Cube" is now on his fifth motor my other mate (Trek) two however he has just had the dreaded "error message" which probably means a new motor. So three guys, four bikes, eleven motors - scary! Average age of our group is 67 ! So no crazy riding. Maintenance best described as fastidious, no direct blasts with a with a hosepipe and deffo no jet washing. Bosch replied to my issues stating "they develop their motors / products based on customer feedback". Last motor for me if it fails out of warranty I will buy something cheaper to run. Something like a Bugatti Veyron.

 

[Stihldog]

IMO the most reliable motor is the Bosch CX Gen4. That’s been in my Rail since 2019 and I’ve only recently decided to have it rebuilt. Only because I heard a little noise coming from the motor area …which may have been a loose castle nut. Oh well, after less than 20K km on that motor it’s probably about time.

I’ve installed the bearing seal kit a couple of times during that period so that may have helped prolong the life …even though I’m a prolific motor abuser.

The recent motor brands are improving but I still see other eMTB motor manufacturers down for warranty or replacement. Thankfully motor rebuild centres are popping up. I’m not too concerned about motor preformance/speed but rather motor longevity and reliability.

Occasional maintenance and proper cadence is key. Pedal strikes are gonna happen. Water is unavoidable.

 

[irie]

Thankfully motor rebuild centres are popping up.

@TDM Cube if you're in the UK then your first port of call for out of warranty motor repairs should be:

eBike Motor Repairs & Servicing - Homepage

eBike Motor Parts Repairs & Servicing, (formally, Performance Line Bearings) has become the “go to place” for all your e-Bike motor repairs...

www.ebikemotorcentre.com

 

[Gareth]

I think your experience is fairly typical.

My first motor lasted about two and a half years and 3400 miles. The refurb I bought lasted about 200 miles before needing a rebuild. Not used the bike as much over the last year, but so far so good on the rebuilt refurb.

I used to hose the bike down, but not anymore – hand wash only.

This thread might be of interest to you;

Bosch Gen4 Seal Service & Grease up

As you probably know Bosch consider the unit to be a sealed non-serviceable unit. They do not sell spares. There is hope that new EU right to repair legislation may change this sad pain in the arse situation.

Anyway, if, or rather when your motor inevitably fails again and you are outside of warranty, then your best bet is probably the ebike motor centre eBike Motor Repairs & Servicing - Homepage

And hopefully there is some good news. The ebike Motor Centre have recently launched an upgrade for the Gen4 Bosch, which will hopefully help keep the water out – which is the number one cause of motor death.

Bosch Gen 4 Upgrade Service - eBike Motor Centre (Performance Line Bearings)

At eBike Motor Centre we noticed a failure pattern on the Bosch Generation 4 motors when used on EMTB’s. We could also see from our own experience, and the sheer number of Bosch Gen 4 motors going through our workshop, there were a few issues that needed addressing, particularly when used...

www.ebikemotorcentre.com

The other thing to consider is seeking help before the motor dies. If you motor has any significant play in the bearings, has an intermittently sticky sprag clutch, is shutting down and showing error messages,then it is a good idea to seek help before it dies.

 

[Stihldog]

I think your experience is fairly typical.

My first motor lasted about two and a half years and 3400 miles. The refurb I bought lasted about 200 miles before needing a rebuild. Not used the bike as much over the last year, but so far so good on the rebuilt refurb.

I used to hose the bike down, but not anymore – hand wash only.

This thread might be of interest to you;

Bosch Gen4 Seal Service & Grease up

As you probably know Bosch consider the unit to be a sealed non-serviceable unit. They do not sell spares. There is hope that new EU right to repair legislation may change this sad pain in the arse situation.

Anyway, if, or rather when your motor inevitably fails again and you are outside of warranty, then your best bet is probably the ebike motor centre eBike Motor Repairs & Servicing - Homepage

And hopefully there is some good news. The ebike Motor Centre have recently launched an upgrade for the Gen4 Bosch, which will hopefully help keep the water out – which is the number one cause of motor death.

Bosch Gen 4 Upgrade Service - eBike Motor Centre (Performance Line Bearings)

At eBike Motor Centre we noticed a failure pattern on the Bosch Generation 4 motors when used on EMTB’s. We could also see from our own experience, and the sheer number of Bosch Gen 4 motors going through our workshop, there were a few issues that needed addressing, particularly when used...

www.ebikemotorcentre.com

The other thing to consider is seeking help before the motor dies. If you motor has any significant play in the bearings, has an intermittently sticky sprag clutch, is shutting down and showing error messages,then it is a good idea to seek help before it dies.

I’m currently using a spare motor in my bike while I send out my original motor to be fully serviced. I’m not Sean btw.


This motor had broken bracket bolts in the casing of the drive side. The Motor repair centre sent me a replacement casing for a very reasonable price. It sits on my shelf as a spare so none of us go without for more than a week. A complete replacement motor can take months to get …and those are never in stock at your LBS.

I hope to get the latest and greatest rebuild for my Bosch Gen4 motor from CycloChrome in Quebec Canada. Cheaper than a replacement me thinks.

 

[Gareth]

I’m currently using a spare motor in my bike while I send out my original motor to be fully serviced. I’m not Sean btw.

This motor had broken bracket bolts in the casing of the drive side. The Motor repair centre sent me a replacement casing for a very reasonable price. It sits on my shelf as a spare so none of us go without for more than a week. A complete replacement motor can take months to get …and those are never in stock at your LBS.



I hope to get the latest and greatest rebuild for my Bosch Gen4 motor from CycloChrome in Quebec Canada. Cheaper than a replacement me thinks.

So I’ve gone a similar but different route. For a number of reasons, I bought another ebike. Those are that I suspect I’m going to be made redundant sometime in the next year – so decided a good idea to bag another c2w bike, as redundancy should spell retirement for me. Then there is the Bosch Gen5 – which I want to avoid as I bet it’ll leak like a sieve just like the Gen 4. I am hoping that the ebike motoro centre motor seal upgrade for the Gen4 is a success and might save my motor once out of warranty. A seal upgrade for the Gen5 could be a long way off (assuming it is required)

I’m guessing you are using the non-smart motor Sean, sorry Stihldog, as my understanding is you can’t switch the smart motors over easily with the smart system (if that is correct that’s another royal pain in the arse)

So anyway, I am a hopeless emtb ebike addict, desperately hoping some of the lessons leant from my Cube will save me from bankruptcy with the Mondraker. We shall see.

 

[TDM Cube]

Thank you all for your informative replies and videos. All were very helpful and appreciated.

 

[Paulquattro]

Welcome to the forum

 

[Stihldog]

…motor Sean, sorry Stihldog,

bahahaha.…I’m guilty of tinkering with other bikes so I use permanent markers to keep track of things …I must be easily confused and forgetful. (Sean is my neighbor, I’m just a Hand-held-power-TOOL!!!!)

I always weigh my options; Do I buy the tool or send it away? I guess it depends on my ability, time, interest, need etc. Rebuilding a motor is possible for me but there’s a can-of-worms…so I’ll send it away. I’ll stay in this lane for now. The bearing seal kit is as far as I want to go right now.

I can’t bake a cake …but I can lace a wheel.

 

[Stihldog]

Welcome to the forum

Doooh! I forgot to mention that.

Welcome to the forums.
Cheers

 

[Mister cube]

Hi all, my first message so please be gentle! Riding a Cube action emtb on a regular basis with my two mates for just under four years. The ever increasing cost of consumables (tyres, pads, chains, etc) is a concern but I get that the extra power from the motor does make things wear out a bit quicker. The real issue is the reliability of the Bosch gen 4 motor. Reading posts this is an issue that has gone on for years. My first motor failed after 2.5 years Bosch did a "goodwill deal" and offered 50% off. The replacement motor lasted 13 months and this was replaced under warranty December 2024. I now have 11 months warranty left. If it fails after this time its going to cost close to a £1,000.00. Am I unlucky? One of my mates "Trek and Cube" is now on his fifth motor my other mate (Trek) two however he has just had the dreaded "error message" which probably means a new motor. So three guys, four bikes, eleven motors - scary! Average age of our group is 67 ! So no crazy riding. Maintenance best described as fastidious, no direct blasts with a with a hosepipe and deffo no jet washing. Bosch replied to my issues stating "they develop their motors / products based on customer feedback". Last motor for me if it fails out of warranty I will buy something cheaper to run. Something like a Bugatti Veyron.

Have you maintained it properly?
i take the cranks off and re do the bearing seals,every 5-6 months,easy job to do,just clean and re apply tacky grease,then re assemble
my gen 4 has now covered 2000 miles in 20 months,and ive never had an issue with it,and it gets ridden in all weathers.

 

[schra]

Good experience here with a Bosch gen4 trek rail, after 5500km and 2 years i opened up the motor for inspection, only a little bit of water/moist inside on drive-side, so replaced that bearing and greased up.
the absolute most important thing is keeping water out, so no washing with water and every few month some extra grease on the seals.

 

[edruid]

What's wrong with washing mud off with a garden hose? I ride all yar round and the hose has got nothing on the shit my bike (Cube / Bosch) gets in its face on the trails. I don't buy into the idea MTBs can't take a hosing, they need to be built well enough for that not to be an issue. To be clear, I concede a pressure washer is really asking for trouble...

 

[Mad_Angler1]

Pressured water seems to be the key issue.

Has anyone considered some shields for that area. Some cups that would offer some protection at least. Large enough not to seal in water but enough not allow direct spray in .

Could 3d print them in TPU tbh. I may have a look.

 

[Stihldog]

Good experience here with a Bosch gen4 trek rail, after 5500km and 2 years i opened up the motor for inspection, only a little bit of water/moist inside on drive-side, so replaced that bearing and greased up.
the absolute most important thing is keeping water out, so no washing with water and every few month some extra grease on the seals.

I did the same but not because of noise or failure. Some bracket bolts had broken. When I opened up the motor I noticed some clear fluid or water around the perimeter of the gasket. I also noticed a slight dis-colouration of grease on the gears. It looked like rust but I could not find any evidence of rust or pooling water. It was explained to me that some grease can emit moisture over time.

I have submerged my bike several times (different Bosch motor) over the years with no noticeable effects. Ride in all types of weather and wash (garden hose shower) when needed. Since I was read the “riot act” by Mrs Stihl I don’t track any dirt into the house.…anymore.

Looks like rust to me …but the gear was fine. Maybe that’s the colour of the grease?

 

[Gareth]

What's wrong with washing mud off with a garden hose? I ride all yar round and the hose has got nothing on the shit my bike (Cube / Bosch) gets in its face on the trails. I don't buy into the idea MTBs can't take a hosing, they need to be built well enough for that not to be an issue. To be clear, I concede a pressure washer is really asking for trouble...

I’m not hosing mine down anymore. I got a mere 3400 miles out of the motor before it died with water ingress. And that was just after I had every pivot bearing on the bike replaced – they were absolutely destroyed and some of them seized solid.

Rear hub has been replaced and I’ve fitted a new front wheel. I think Cube ‘newman’ hubs are maybe a bit soft.

But yes, I am concerned that my liberal use of the garden hose may have not only destroyed the motor but taken out all the pivot bearings.

It is not that hard to wash by hand. Bought a set of muc-off brushes and that helps.

We will see how it goes.

Have you maintained it properly?

These units are officially maintenance free. There is no maintenance schedule. But yes, it appears to be good practise to do those seals. Something I need to get round too.

 

[Mister cube]

I’m not hosing mine down anymore. I got a mere 3400 miles out of the motor before it died with water ingress. And that was just after I had every pivot bearing on the bike replaced – they were absolutely destroyed and some of them seized solid.

Rear hub has been replaced and I’ve fitted a new front wheel. I think Cube ‘newman’ hubs are maybe a bit soft.

But yes, I am concerned that my liberal use of the garden hose may have not only destroyed the motor but taken out all the pivot bearings.

It is not that hard to wash by hand. Bought a set of muc-off brushes and that helps.

We will see how it goes.



These units are officially maintenance free. There is no maintenance schedule. But yes, it appears to be good practise to do those seals. Something I need to get round too.

Newmen hubs and wheels which cube use are utter shite,when i bought my cube stereo,i immediately junked the wheels and had some decent ones made with hope hubs,cost cutting on most makes is always crap wheels

 

[Gareth]

Newmen hubs and wheels which cube use are utter shite

Newman is Cube’s wheel brand.

I’ve got a hope hub on the rear laced onto the Newman rim on my old Cube. The Newman hubs seem a bit soft. The front I now have a DT Swiss wheel. Will see how they go.

My Mondraker has Mavic Wheels, apart from the dreadful lettering on the rims they look pretty good and sturdy, the hubs are chunky, but yeah we’ll see how they go.