Tongsheng crank wobble - can I use Loctite?

[Jimrat]

Hi

After 3 weeks of use and 350 miles, I've noticed a couple of worrying issues with my Tongsheng mid-motor:

1) The chain ring wobbles +/- 1mm, enough for it to catch on the motor housing and make a scuffing sound
2) The pedals wobble +/- 1mm in/out/up/down

Neither are caused by loose motor mountings - everything is rock solid. I've removed the crank spindle and there seems to be two problems:

There's a lot of lateral play in the sprag clutch bearing (that holds the chain ring);
The bearings that support the crank spindle are a very loose fit on the shaft (the shaft has been polished by the slippage - see photo). I've bought new spindle bearings and sprag clutch

Question 1: can I use Loctite 638 to lock the bearings onto the spindle / into the housing to reduce the wobble? Is it OK to get loctite on the woodruff key area between sprag clutch and torque sensor?

Question 2: - is this unit made of cottage cheese or have I just been unlucky? It's only been used for commuting on flat UK roads, not off-road single track or steep gradients

Thanks
Jim

 

[Sturmey]

Hi. I have some similar type looseness/wobble after a few hundred Km but its not so bad as to cause scuffing. The left side seems to be worst and I have seen it suggested (endless sphere) that another second bearing can be made to fit in here, although there is some concern about how to remove afterwords. Other suggestions is to pack bearing with thin 'feeler gauge' as a shim or using loctite 'bearing mount' (609?).
It goes without saying that I am disappointed to see what looks like wear at such an early stage and am much of the time back using my other bike with old Bafang hub motor and 22 thousand km on motor which has never given any trouble (other than a few broken spokes and water getting into pas sensor once). I need the middrive only on the steep hills and can transfer battery from one bike to another..
I don't know what happens if you ignore the wobble, i.e. Does it get worst or cause damage?

 

[Jimrat]

Hi Sturmey,

Thanks for the reply. I have come to the same conclusions as you, and will try a combination of: shims; extra spindle bearing; and loctite. I also posted the same question on Endless Sphere and apparently PSPower sell a wave washer that fits inboard of the circlip on the non-drive end of the spindle to take up the slack.

I'll report back with results next week hopefully.

Regards
James

 

[Jimrat]

I don't know what happens if you ignore the wobble, i.e. Does it get worst or cause damage?

As soon as I noticed the wobble I stopped using it, for fear of damaging the torque sensor.

 

[Sturmey]

As soon as I noticed the wobble I stopped using it, for fear of damaging the torque sensor.

These guys claim that they contacted pswpower (april 2019) and was told that the wobble in axle was normal, so I reckon I will still keep using the bike.

New "TSDZ2 Torque Sensor Central Motor"

Hi, I was made aware of a new offering over at BMSBattery today: "SDZ2 Torque Sensor Central Motor". https://bmsbattery.com/home/803-sdz2-torque-sensor-central-motor.html Seems like a an attractive alternative to the Bafang BBS, $50 cheaper, with torque sensor, better installation guide etc...

endless-sphere.com

 

[Jimrat]

Hi

Just to update this thread:

Reduced the chain ring wobble by fitting a new sprag clutch. There's still a small amount of lateral play, but much better and not scuffing on casing.

Reduced the pedal / crank wobble as follows:
At the drive end of the spindle: I was able to slide a piece of 0.1mm feeler gauge between the spindle and the torque sensor.
At the non drive end of the spindle: I fitted an extra bearing behind the dust cap; was able to slide a piece of 0.04mm feeler gauge between spindle and outer bearing; and used loctite 638 on both bearings, but only between spindle and inner race.

The SKF bearings I used were a tighter fit in the bottom bracket tube, so I needed to use a 19mm deep wall socket to tap them into place. I didnt use loctite on the outer surface (between bearing and bottom bracket tube), so should still be able to tap the whole spindle out from the drive side if I need to dismantle in the future.

Put 50km on it yesterday and it is was fine

Cheers
Jim

 

[Sailorbass]

Similar problem here. left side (non-drive side) crank keeps coming loose on my Tongsheng ebike conversion. First, I get a ticking noise that quickly becomes a knock. Tightening the crank bolt seems to solve the problem for a short while, but then it recurs. I worried that I'll damage the motor spindle and or torque sensor if I keep re-tightening the crank bolt. Drive side crank bolt seems OK. Don't want to faff about with feeler gauge shims. Easiest fix?

Use loctite on crank bolts?
Replace crank arms and bolts with new ones? Suggestions for new cranks, please?

 

[Sturmey]

Similar problem here. left side (non-drive side) crank keeps coming loose on my Tongsheng ebike conversion. First, I get a ticking noise that quickly becomes a knock. Tightening the crank bolt seems to solve the problem for a short while, but then it recurs. I worried that I'll damage the motor spindle and or torque sensor if I keep re-tightening the crank bolt. Drive side crank bolt seems OK. Don't want to faff about with feeler gauge shims. Easiest fix?

Use loctite on crank bolts?
Replace crank arms and bolts with new ones? Suggestions for new cranks, please?

I think yours is a different problem in that in your case it appears to be just the crank arm coming loose on the spindle. The solution then would be to just replace the left side crank arm . I think the relatively common standard square taper(170mm ?) crank arm will fit so it should be easy to get at local bike shop etc. I have fitted a pair of steel (155mm) cranks from a scrap budget junior mtb on mine with no problems other than grinding off the chainring.

 

[Nealh]

Jis is the standard used for square taper cranks arms, the tsdz2 offer up quite a wide Q factor and quite a few folks use Bafnag BBS arms as a replacement. Also one can use ebike cranks like fsa ck220 used on other ebike mid drive that use Square taper.