Motor question with motorised kayak if I may (70131 12kw Waterproof Brushless Motor for E-foil)

First a bit about myself,
I am a 70 year old retired Dutch chap that lives in Wales (UK) 500metres from the sea.
Logically in my opinion I wanted to do something on the water that is doable so the kayak was the plan, but as an engineer of sorts it had to be motorised, hence the 70131 12kw.

I have been out on the water a few times for short trial runs. At first with a 5 kW controller meant for scooters and such but it’s not as free running as it was and on land the motor runs hot quickly and than it failed on me…
I have now compiled a new plan with an ESC ( [T-Motor Flame 80A HV PRO OPTO ESC Speed Controller 6-12S / RC Drone Quadcopter) I bought once second hand and that works with relay for reverse etc. (I now have a new esc on order that has built-in reverse)

So the question for someone with experience on these motors is: what can the reason be for the prop shaft to run stiff after less that an hour running over about 5 months time. Is it ingress of seawater?
And what type of seals are used in these motors? Can I give it an overhaul?

Looking forward to any advice
Happy water fun times


It could be water ingress, you might be abe to save it if you open it and replace the bearings
(and possibly seal). Motors for efoils use either rubber seals with a lip or ceramic seals, see here, further down: Efoil motor FS65161 100KV 6000W 20S water proof for motorized surfboard | – FLIPSKY

More information on how to take it apart and how it looks inside: MP70131 anyone tried - #61 by tacktun

That’s fab, thanks for the info.
I’ll test run it further this weekend at sea and see how it holds. As the motor sits in the water it should be cooled better that in the air and it should run free after some running.
I’ll can post some pictures of my motor fittings if there is interest :slight_smile:

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Hi, I have the same motor running, not in seawater but I am sure that the sidescrews could be a reason, they are not stainless steel. Which is a shame for an underwater motor. Replaced them for about 2EUR.If you search here for 70131 in the forum you will find pictures from the inside of the motor. For good and not hot running I can say vesc 75200 does a good job.But needs to get correct settings automatic foc detection mode does no work and vesc got forward and backward option also. Greetings

Thanks Sharrow for that. I have now on order a 400A Brushless Two-way Water-cooled ESC Applicable Voltage 8-70V as it has as far as I could see all the right specs needed for the job without being delicate. I use 48v batteries and not the allowable 70v as this could kill me on water…

I will check the screws tomorrow to see if they are stainless steel or not, thanks for that, good call!

I made a frame of 40mm high pressure water pipes in which the motor sits with a approx 5mm gap around it.

I can also provide the fliteboard propeller for the 70131. costs about 50 EUR and does not over power the motor and therefore the esc. Thats the main reason for getting the esc too hot. Only have to drill the hole from the prop from 8mm up to 10mm for fitting the 70131 thats it, problems should be gone after that.

For your motor holder I would say it cost you a lot of efficiency. It is too big. Put the motor not in the back, better under your feet and use a 70mm aluminium pipe with 4mm wall thickness as an holder for the motor. Tomorrow I can send you pictures from my holders if you want.

Hi Sharrow, I thought that I replied earlier but I must have done something wrong as it’s not here… :wink:
The plan is to make the motor support assy in Stainless steel at some point. For now it is in PVC as I can modify that, within limits. I plan to fit the motor to what is now the rudder swivel point with support arms to the bottom/sides of the kayak. As I have to move the kayak over land and beach I am not so fond of letting it sticking out below the keel to prevent damage, both on land and in the bay where there are some rocks.
I had another go yesterday, the water was calm and everything worked, including the servo driven rudder, until the little esc overheated. But as I have a suitable one on order I am not too worried.
Thanks for communicating because this water stuff is all new to me

If you got servo driven rudder, its good Position then. I got no tools for stainless steel. So I went for aluminium, its also lighter. Good luck and keep informing us. You can do the rouder clamp like mine. Works really good and its easy to install

I have the 70141 and True the vesc automatic motor set up is not running on them.
What is the correct parameter to type ?
20 pols
I want to limit mine to 100amp on the motor
And max amp 160.
Any other information please:)?

Hi Alex2, I googled your question and found this answer:

I hope this helps

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As I have destroyed an underpowered air cooled ESC I have now received a 400 amp water cooled model. As I could not find information on the net about how much heat such unit produces I had a test to dee if the fan and pump control board could keep the temperature below 40C, and it did. (Heated a copper pipe in the water circuit with 300C hot air from a heat gun… )
These two pictures show what I am going to place inside the kayak after I have completed the electrical power connections. (fingers crossed)

I have some experience with the bigger brother 70141:)
I think or vibration of the prop cracked the ceramic shaft seal and allow water in.
Or the magnets on the rotor get loose and stuck inside. I suggest you open the motor very carefully using bearing puller .as if you hammer on it that can easily crack the ceramic shaft seal if it hasn’t been cracked already:).
There are 4 screw next to the cap .open them and remove the cap slowly slide it open on the shaft and have a look inside:).
Good luck

I am now in contact with the supplier of this motor as there has to be something wrong with the one I have for it not to run after less that an hour use…
They are very good and after some initial discussion/questions and indeed the motor still makes its “bleep” sounds" so that is good. Then they asked me to open the motor. Lo and behold there is water inside and it is a bit of a mess. The seal is smooth intact, the bearings feel rough and the Aluminium of the rotor has corroded in a small section. Probably seawater has got inside on the first trial and has sat there during the winter… Now waiting for their advice and as to what’s the plan of repair…

Quick update about what is going on.
I am still in contact with the supplier of my motor but haven’t come to a conclusion yet.
Working back as to how much time this motor has been “under water” I came to the shocking conclusion that that is about an hour or two of which the first 10 minutes was last year. The water must have got in the motor then and had chance to do its damage during the winter. We haven’t concluded where the water has entered but in my opinion the two big O-rings are possible culprits. The one on the end bell had 4 nips out where it went past the thread of the holding screws…
Hopefully I will receive a replacement motor soon as summer is nearly over :frowning:

Update for those interested.
As I have had no success obtaining a replacement for my leaking motor from the manufacturer nor the shop “Btree Hobby Store” in China I have decided to make a repair attempt myself. If that promised replacement motor never arrives I hopefully have at least something to power my kayak with, albeit next year…


The waterproof IP68 BLDC inrunner motor, advertised for eFoils, Foils and Lift foils, in other words “you can use this motor under water” is not waterproof. Not only that, the shop I purchased this motor from via AliExpress has so far not succeeded to get a replacement motor or parts under warranty from the manufacturer. The fault therefore lies not so much with the shop nor AliExpress but with the manufacturer of the motor. This motor has in total been less than 3 hours in the sea and has already taken water in during the first trial of about 10-15 minutes, during which it has not even been running! Whilst I was working on the battery box and controls etc, during the winter the seawater has corroded the Aluminium parts and magnets of the motor. My conclusion therefore is that this motor is not fit for purpose!


So, 4 months later and none the wiser I decided to start repairing the motor myself and break the silence here so that perhaps someone can benefit from my trials and/or help me out when I get stuck.

Five of the motor magnets were loose when I opened the motor, one of which had broken and that one actually was the cause of the motor jamming. The others were loose too when I wriggled them a bit and came out easily. I removed the rust from them there where they were bonded to the rotor and coated them with metal primer. Following that I machined about 0.4mm of the Aluminium core, roughened it up and applied a light coating of epoxy which after curing I machined back to the original size. Next I placed the original magnets back on a thin bed of 2216 (from 3M) and tied that down with 4 tie straps although the magnets want to pull themselves “in” already. I should have somewhere “in a box” some Kapton tape that I want to wind around the whole lot. The idea is that that take will take the strain from the centrifugal forces off the bonded magnets keeping the whole lot together. I also have the option to apply a layer of thin brass sheeting around the magnets first but I am not sure if that will have a negative influence on the magnetic fields.

As I suspect the the water ingress has been via the motor shaft I will modify the end bell so it can take a double lip shaft seal before the pump shaft seal. I plan to add thin oil in the space between the two. Also, as the bearings both have seized up because of water ingress I will replace them with 2RS bearings to which I will also add additional lubricant.

Looking forward to commends and advice,


Another bad story on freerchobby parts.

My advice for everyone: choose a different manufacturer.