WR-02CB gearbox locks up with motor installed

[hanzo 9]

Greetings,

First post on Tamiya Club.

I have problem with one of my cars and wondering if anyone has experienced this before.

The car ‘Comical Grasshopper’ WR-02CB has been running fine for the last couple months. I decided to swap the stock 18T pinion out and install a 20T steel pinion.  After I did the swap, the motor (Super Stock BZ) could not turn the gears. Doesn’t make sense I know :-(.

I removed the motor, and confirmed the gears are rotating freely.

I can also rotate the left gearbox joint and right gearbox joint independently clockwise (forwards) and anti-clockwise (backwards).  And both together clockwise and anti-clockwise. 

It’s when I install the motor (mount in the 18T 20T holes) everything locks up if I try to rotate both left and right gearbox joint forwards or backwards.  

With motor mounted I can rotate each left/right independently.  ie. If I rotate left gearbox joint clockwise, the right gearbox joint will rotate anti-clockwise and visa versa.

I have un-assembled/re-assembled the gearbox numerous times to make sure it is indeed assembled correctly and I’m sure it definitely is.

I have an old Wild Willy 2 WR-02 chassis and can rotate both the left and right back wheels forwards and backwards which will turn the motor.

For this Comical Grasshopper WR-02CB, I can’t for some strange reason.  I think I have run out of ideas.

Thanks.

[ThunderDragonCy 7873]

You need to install using the 20t holes on the chassis. That will work fine. Make sure the pinion is installed at the correct height from the motor as well. 

[hanzo 9]

Apologies, typo on my part - it was mounted using the 20T holes.  

The pinion height is set to 14mm as per the manual.  If I open up the gear box, I can see the pinion setting on the Counter gear (small) comfortably.

I will re-check, and amend my post.

[wolfdogstinkus 1893]

Is it just the stronger motor magnets? Or your aging digits?

Whack a battery on and see if it spins.

[TurnipJF 9182]

Are you certain that the pinion is the correct pitch and has the correct number of teeth? It is rare, but sometimes they are marked incorrectly.

[ThunderDragonCy 7873]

9 minutes ago, TurnipJF said:

Are you certain that the pinion is the correct pitch and has the correct number of teeth? It is rare, but sometimes they are marked incorrectly.

Good point. They use a 0.6mod pinion. If you have got a 0.8mod it will be miles too big. 

[Mahjik 197]

Welcome hanzo,

 

Have you tried putting back the original 18T pinion to see if it spins again?  The reason I ask is that it's possible the current problem has nothing to do with the pinion itself, but just a coincidence that it happened when changing the pinion.

 

[waterbok 1282]

Did you use the same screws for the motor or maybe swapped for longer screws. This can also cause the motor to lock up if the screws hit the rotor.

[hanzo 9]

15 hours ago, wolfdogstinkus said:

Is it just the stronger motor magnets? Or your aging digits?

Whack a battery on and see if it spins.

That's what I thought and I tried that, but didn't spin.  I was suspecting my ageing digits for sure mate :-)

15 hours ago, TurnipJF said:

Are you certain that the pinion is the correct pitch and has the correct number of teeth? It is rare, but sometimes they are marked incorrectly.

I did check, I was using the 20T pinion from Tamiya 50356 which I believe is 0.6.

12 hours ago, Mahjik said:

Welcome hanzo,

 

Have you tried putting back the original 18T pinion to see if it spins again?  The reason I ask is that it's possible the current problem has nothing to do with the pinion itself, but just a coincidence that it happened when changing the pinion.

 

Thank you. :-) Yes, I did put it back and used another motor but had the same issue.

12 hours ago, waterbok said:

Did you use the same screws for the motor or maybe swapped for longer screws. This can also cause the motor to lock up if the screws hit the rotor.

When I saw your post, it jogged my memory.  A couple of weeks ago I added a Hop-up (Tamiya 54817 Motor Guard for Wr-02/gf-01) which included longer screws - 3x28mm.

WR-02CB screws from the kit MG1 3x25mm.

I used the original screws (3x25mm) without the motor guard and the gearbox spun as expected. Thank you so much!

I then re-installed the motor guard (I think it was about 5mm or so think) with the longer screws (3x28mm) but the motor still locked.

Scratched my head for a bit, then re-installed the motor with the motor guard AND the motor plate.  All works as expected.

Who would have known that motor plate would cause the motor to lock up?? I think it was only like 1mm or less thick.  Respect to Tamiya for their precision design/engineering.

Thank you all for the responses fellas, really appreciate it!

[waterbok 1282]

Darn, i am good....   was a bit of a familiar problem